Patent Publication Number: US-2023149052-A1

Title: Facet joint replacement device and methods of use

Description:
INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS 
     Any and all applications for which a foreign or domestic priority claim is identified in the Application Data Sheet as filed with the present application are hereby incorporated by reference under 37 CFR 1.57. 
     The present application is a continuation of U.S. application Ser. No. 16/808,203, entitled “FACET JOINT REPLACEMENT DEVICE AND METHODS OF USE”, filed Mar. 3, 2020, which claims priority benefit of Provisional Patent Application Ser. No. 62/813,678, entitled “FACET JOINT REPLACEMENT DEVICE AND METHODS OF USE”, filed Mar. 4, 2019, and is a continuation-in-part of U.S. application Ser. No. 16/786,753, entitled “FACET JOINT REPLACEMENT DEVICE AND METHODS OF USE”, filed Feb. 10, 2020, which is a continuation of U.S. application Ser. No. 15/836,643, entitled “FACET JOINT REPLACEMENT DEVICE AND METHODS OF USE”, filed Dec. 8, 2017, now U.S. Pat. No. 10,555,761, which is a continuation of U.S. application Ser. No. 15/472,021, entitled “FACET JOINT REPLACEMENT DEVICE AND METHODS OF USE,” filed Mar. 28, 2017, now U.S. Pat. No. 9,839,451, which claims priority benefit of U.S. Provisional Patent Application Ser. No. 62/314,634, entitled “Restore Unilateral or Bilateral Artificial Lumbar FACET joint surgical implant,” filed Mar. 29, 2016, the entire disclosure of each of which is hereby expressly incorporated by reference. 
    
    
     BACKGROUND 
     Field 
     The present application relates to spinal surgery in general, and more particularly to methods, systems, and apparatuses for replacing a facet joint. 
     Description of the Related Art 
     The lumbar facet joint is a diarthrodial synovial joint consisting of a superior articular process having a superior articular surface, an inferior articular process having an inferior articular surface, and a capsule that encloses the superior and inferior articular surfaces. Each lumbar facet joint can provide mechanical support for axial loading along the spine, facilitate movement along a longitudinal axis of the spine, and limit relative rotation and translation of adjacent vertebra. Particularly, the articular processes support compressive loading and the capsule, resists forces developed across the facet joint due to movement of the adjacent vertebrae, such as, for example, rotational and translational forces. The facet joint capsule can provide resistance to separation of the superior and inferior articular surfaces and to relative motion between the superior and inferior articular surfaces. 
     Lumber facet joint dysfunction can develop as a result of degeneration, trauma, or neoplastic processes to the vertebrae and can result in spinal instability, malalignment, nerve compression, and pain, which can cause neurological deficits. Facet joint dysfunction is treated by partial or total resection of the dysfunctional lumbar facet joint. Resection can leave the addressed spinal motion segment with decreased strength, stiffness, and the ability to resist rotation. 
     Fusion procedures have evolved to address the spinal de-stabilization of motion segments caused by facet joint resection. Fusion procedures result in immobilization of the two adjacent vertebrae that comprise the motion segment. As physiologic loads are transmitted across contiguous motions segments of the lumbar spine, the introduction of an immobilized motion segment within the lumbar spine can result in non-physiologic transmission of these forces. This “disconnection” within the series of motion segments that comprise the lumbar spine has been postulated to create an altered force load application on the adjacent, non-treated, motion segments, potentially accelerating the degenerative process at these locations. 
     SUMMARY 
     Methods, systems and apparatuses are provided in certain embodiments of the present application to replace a dysfunctional facet joint. 
     In one embodiment, a facet joint replacement device is provided. The facet joint replacement device includes an enclosing element including an enclosing body and an inferior attachment member. The enclosing body includes a superior end having an opening, an inferior end, and an inner cavity defined by an interior surface of the enclosing body, wherein a portion of the interior surface of the enclosing body forms a superior articulating surface. The inferior attachment member extends from the enclosing body and is configured to attach to an inferior vertebral body. The facet joint replacement device also includes an inferior articulating element including an articulating body and a superior attachment member. The inferior articulating body is positioned within the inner cavity of the enclosing body of the enclosing element and is configured to move within the inner cavity of the enclosing body of the enclosing element. The inferior articulating body includes a superior end and an inferior end forming an inferior articulating surface. The superior attachment member extends from the superior end of the articulating body and superior to the opening of the superior end of the enclosing body. The superior attachment member is configured to attach to a superior vertebral body. The movement of the articulating body of the inferior articulating element is constrained in at least one direction within the inner cavity of the enclosing body of the enclosing element. 
     In another embodiment, a facet joint replacement system is provided. The facet joint replacement system includes the facet joint replacement device, an inferior fastener configured to secure the inferior attachment member to the inferior vertebral body, and a superior fastener configured to secure the superior attachment member to the superior vertebral body. 
     In another embodiment, a method of implanting a facet joint replacement device is provided. The method includes providing the facet joint replacement device, securing the superior attachment member to the superior vertebral body, and securing the inferior attachment member to the inferior vertebral body. 
     In another embodiment, a method of replacing a facet joint is provided. The method includes resecting at least a portion of a facet joint defined by an articular process of a superior vertebral body and an articular process of an inferior vertebral body, cannulating a pedicle of the inferior vertebral body and a pedicle of the superior vertebral body, inserting a first fastener into the pedicle of the inferior vertebral body and a second fastener into the pedicle of the superior vertebral body, and securing a facet joint replacement device to the first fastener and the second fastener, wherein the facet joint replacement device includes an enclosing body, an inferior articulating surface enclosed within the enclosing body, and a superior articulating surface enclosed within the enclosing body. 
     In another embodiment, a facet joint replacement system is provided. The facet joint replacement system includes a facet joint replacement device. The facet joint replacement device includes an enclosing body and an articulating body. The enclosing body includes an interior surface defining an inner cavity of the enclosing body. The interior surface includes a first articulating surface and a projection extending inwardly relative to a surrounding area of the interior surface. The articulating body is positioned within the inner cavity of the enclosing body and is configured to move within the inner cavity of the enclosing body. The articulating body includes a second articulating surface and a recess extending inwardly relative to a surrounding area of the articulating body and aligned with the projection of the interior surface of the enclosing body so as to allow movement of the projection along the recess of the enclosing body while constraining rotational motion of the articulating body within the enclosing body. 
     In another embodiment, a facet joint replacement system is provided. The facet joint replacement system includes a facet joint replacement device. The facet joint replacement device includes an enclosing body and an articulating body. The enclosing body includes an interior surface defining an inner cavity of the enclosing body. The interior surface includes a first articulating surface. The enclosing body includes a first channel extending through a portion of the enclosing body. The articulating body is positioned within the inner cavity of the enclosing body and is configured to move within the inner cavity of the enclosing body. The articulating body includes a second articulating surface and a second channel extending through at least a portion of the articulating body. The facet joint replacement system also includes a fastener configured to be removably received within the first channel and the second channel, the fastener configured to engage the enclosing body and articulating body to constrain movement of the articulating body within the enclosing body, and a plug configured to be removably received within the first channel. 
     In another embodiment, a facet joint replacement system is provided. The facet joint replacement system includes a facet joint replacement device. The facet joint replacement device includes an enclosing body and an articulating body. The enclosing body includes an outer shell defining an exterior surface of the enclosing body and a liner covering an interior surface of the outer shell, the liner including a low friction material and defining an inner cavity of the enclosing body, a portion of the liner defining a first articulating surface. The articulating body is positioned within the inner cavity of the enclosing body and is configured to move within the inner cavity of the enclosing body. The articulating body includes a second articulating surface configured to articulate against the first articulating surface. 
     In another embodiment, a method of replacing a facet joint is provided. The method includes introducing a facet joint replacement device into a body of a patient, the facet joint replacement device including an enclosing body and an articulating body positioned within an interior cavity of the enclosing body, wherein a fastener is positioned with respect to the enclosing body and the articulating body to constrain movement of the articulating body within the enclosing body. The method further includes securing the facet joint replacement device relative to a superior vertebral body and relative to an inferior vertebral body of the patient while the fastener constrains movement of the articulating body within the enclosing body. The method further includes removing the fastener after securing the facet joint replacement device relative to the superior vertebral body and relative to the inferior vertebral body to allow movement of the articulating body within the enclosing body. 
     In another embodiment, a facet joint replacement device is provided. The facet joint replacement device includes an enclosing body and an articulating body. The enclosing body is configured to be secured relative to one of a superior vertebral body and an inferior vertebral body. The enclosing body includes a first articulating surface. The articulating body is configured to be secured relative to the other of the superior vertebral body and the inferior vertebral body. The articulating body is positioned within an inner cavity of the enclosing body and includes a second articulating surface positioned within the inner cavity configured to articulate relative to the first articulating surface. When the enclosing body and the articulating body are secured relative to the superior and inferior vertebral bodies, the first articulating surface and the second articulating surface are configured such that they are located approximately at the location of a natural facet joint and are configured to articulate relative to each other by moving substantially only parallel to a superior/inferior axis of the patient. 
     In another embodiment, a method of replacing a facet joint is provided. The method includes introducing a facet joint replacement device into a body of a patient. The facet joint replacement device includes an enclosing body having a first articulating surface and an articulating body positioned within an inner cavity of the enclosing body having a second articulating surface. The method further includes securing the enclosing body of the facet joint replacement device relative to one of a superior vertebral body and an inferior vertebral body. The method further includes securing the articulating body of the facet joint replacement device relative to the other of the superior vertebral body and the inferior vertebral body, wherein after both the enclosing body and the articulating body are secured, the first and second articulating surfaces are located approximately at the location of a natural facet joint and are configured to articulate relative to each other by moving substantially only parallel to a superior/inferior axis of the patient. 
     In another embodiment, a method of replacing a facet joint is provided. The method includes introducing a facet joint replacement device into a body of a patient, the facet joint replacement device having an enclosing body and an articulating body positioned within an inner cavity of the enclosing body, wherein a device holder is coupled to the facet joint replacement device. The device holder includes a shaft, a handle positioned at a first end of the shaft, and a fastening head positioned at a second end of the shaft, wherein the fastening head is positioned with respect to the enclosing body and the articulating body to constrain movement of the articulating body within the enclosing body. The method further includes securing the facet joint replacement device relative to a superior vertebral body and relative to an inferior vertebral body of the patient while the fastening head constrains movement of the articulating body within the enclosing body, and disengaging the fastening head from the facet joint replacement device after securing the facet joint replacement device relative to the superior vertebral body and relative to the inferior vertebral body to allow movement of the articulating body within the enclosing body. 
     In any of the embodiments described above or elsewhere in this specification, the enclosing body can include a projection extending inwardly relative to a surrounding area of the interior surface of the enclosing body, and the articulating body can include a recess extending inwardly relative to a surrounding area of the articulating body and aligned with the projection of the interior surface of the enclosing body. In any of the embodiments described above or elsewhere in this specification, the projection can be configured to move within the recess parallel or substantially parallel to a longitudinal axis of articulation. In any of the embodiments described above or elsewhere in this specification, the longitudinal axis of articulation can be a superior/inferior axis. In any of the embodiments described above or elsewhere in this specification, the projection can be generally convex, and the recess can be generally concave. In any of the embodiments described above or elsewhere in this specification, the projection can be generally parabolic in shape. 
     In any of the embodiments described above or elsewhere in this specification, the facet joint replacement device can include a first attachment member configured to be secured relative to one of a superior vertebral body and an inferior vertebral body of a patient and a second attachment member configured to be secured to the other of the superior vertebral body and the inferior vertebral body. In any of the embodiments described above or elsewhere in this specification, the first attachment member can be part of the enclosing element, and the second attachment member can be part of the articulating element. In any of the embodiments described above or elsewhere in this specification, the first attachment member can extend from an articulating body. In any of the embodiments described above or elsewhere in this specification, the first attachment member can be configured to be secured relative to a superior vertebral body. In any of the embodiments described above or elsewhere in this specification, the second attachment member can extend from an enclosing body. In any of the embodiments described above or elsewhere in this specification, the second attachment member can be configured to be secured to an inferior vertebral body. In any of the embodiments described above or elsewhere in this specification, the first attachment member can be removably coupled to the articulating body. In any of the embodiments described above or elsewhere in this specification, the first attachment member can be removably secured to the articulating body via a tapered connection. In any of the embodiments described above or elsewhere in this specification, the first attachment member can include a bend in a section of the first attachment member lateral to the articulating body. In any of the embodiments described above or elsewhere in this specification, the second attachment member can be configured to extend from a lateral surface of the enclosing body. In any of the embodiments described above or elsewhere in this specification, the second attachment member can include a bend in a section of the second attachment member lateral to the enclosing body. 
     In any of the embodiments described above or elsewhere in this specification, the first articulating surface can be configured so that it is located approximately at the location of a natural facet joint when the facet joint replacement device is implanted within a body of a patient. In any of the embodiments described above or elsewhere in this specification, the first articulating surface can be shaped, dimensioned, or otherwise configured to correspond to the shape, size, and/or convexity of an articular surface of a healthy superior articular process. In any of the embodiments described above or elsewhere in this specification, the first articulating surface can be configured to perform the functions of an articular surface of a healthy superior articular process. 
     In any of the embodiments described above or elsewhere in this specification, the second articulating surface can be positioned on an anterior and medial section of the articulating body. In any of the embodiments described above or elsewhere in this specification, the second articulating surface can be positioned on a face of the articulating body opposite a recess of the articulating body. In any of the embodiments described above or elsewhere in this specification, the second articulating surface can be configured so that it is located approximately at the location of a natural facet joint when the facet joint replacement device is implanted within a body of a patient. In any of the embodiments described above or elsewhere in this specification, the second articulating surface can be shaped, dimensioned, or otherwise configured to correspond to the shape, size, and/or convexity of an articular surface of a healthy inferior articular process. In any of the embodiments described above or elsewhere in this specification, the second articulating surface can be configured to perform the functions of an articular surface of a healthy inferior articular process. 
     In any of the embodiments described above or elsewhere in this specification, the first articulating surface and the second articulating surface can be configured to articulate relative to each other by moving substantially only parallel to a superior/inferior axis of a patient when the facet joint replacement device is implanted within a body of the patient. In any of the embodiments described above or elsewhere in this specification, the first articulating surface and the second articulating surface can be configured to articulate relative to each other by moving substantially only parallel to an angle formed by the two juxtaposed articular surfaces. 
     In any of the embodiments described above or elsewhere in this specification, an angle between an axis parallel to a frontal anatomic plane and extending through a center point of the first articulating surface and an axis extending through the center point of the first articulating surface and perpendicular to a tangent of the first articulating surface at the center point can be between 30° and 60°, between 35° and 55°, between 40° and 50°, or any other suitable range. In any of the embodiments described above or elsewhere in this specification, an angle between an axis parallel to a frontal anatomic plane and extending through a center point of the first articulating surface and an axis extending through the center point of the first articulating surface and perpendicular to a tangent of the first articulating surface at the center point can be 30°, 35°, 40°, 45°, 50°, 55°, 60°, or any other suitable angle. In any of the embodiments described above or elsewhere in this specification, an angle between an axis parallel to a sagittal anatomic plane and extending through a center point of the first articulating surface and an axis extending through the center point of the first articulating surface and perpendicular to a tangent of first articulating surface at the center point can be between 30° and 60°, between 35° and 55°, between 40° and 50°, or any other suitable range. In any of the embodiments described above or elsewhere in this specification, an angle between an axis parallel to a sagittal anatomic plane and extending through a center point of the first articulating surface and an axis extending through the center point of the first articulating surface and perpendicular to a tangent of the first articulating surface at the center point can be 30°, 35°, 40°, 45°, 50°, 55°, 60°, or any other suitable angle. In any of the embodiments described above or elsewhere in this specification, an angle between an axis parallel to a transverse anatomic plane and extending through a center point of the first articulating surface and an axis extending through the center point of the first articulating surface and perpendicular to a tangent of the first articulating surface at the center point can be between 75° and 105°, between 80° to 100°, between 85° to 95° or any other suitable angle. In any of the embodiments described above or elsewhere in this specification, an angle between an axis parallel to a transverse anatomic plane and extending through a center point of the first articulating surface and an axis extending through the center point of the first articulating surface and perpendicular to a tangent of the first articulating surface at the center point can be 75°, 80°, 85°, 90°, 95°, 100°, 105°, or any other suitable angle. 
     In any of the embodiments described above or elsewhere in this specification, an angle between an axis parallel to a frontal anatomic plane and extending through a center point of the second articulating surface and an axis extending through the center point of the second articulating surface and perpendicular to a tangent of the second articulating surface at the center point can be between 30° and 60°, between 35° and 55°, between 40° and 50°, or any other suitable range. In any of the embodiments described above or elsewhere in this specification, an angle between an axis parallel to a frontal anatomic plane and extending through a center point of the second articulating surface and an axis extending through the center point of the second articulating surface and perpendicular to a tangent of the second articulating surface at the center point can be 30°, 35°, 40°, 45°, 50°, 55°, 60°, or any other suitable angle. In any of the embodiments described above or elsewhere in this specification, an angle between an axis parallel to a sagittal anatomic plane and extending through a center point of the second articulating surface and an axis extending through the center point of the second articulating surface and perpendicular to a tangent of second articulating surface at the center point can be between 30° and 60°, between 35° and 55°, between 40° and 50°, or any other suitable range. In any of the embodiments described above or elsewhere in this specification, an angle between an axis parallel to a sagittal anatomic plane and extending through a center point of the second articulating surface and an axis extending through the center point of the second articulating surface and perpendicular to a tangent of the second articulating surface at the center point can be 30°, 35°, 40°, 45°, 50°, 55°, 60°, or any other suitable angle. In any of the embodiments described above or elsewhere in this specification, an angle between an axis parallel to a transverse anatomic plane and extending through a center point of the second articulating surface and an axis extending through the center point of the second articulating surface and perpendicular to a tangent of the second articulating surface at the center point can be between 75° and 105°, between 80° to 100°, between 85° to 95° or any other suitable angle. In any of the embodiments described above or elsewhere in this specification, an angle between an axis parallel to a transverse anatomic plane and extending through a center point of the second articulating surface and an axis extending through the center point of the second articulating surface and perpendicular to a tangent of the second articulating surface at the center point can be 75°, 80°, 85°, 90°, 95°, 100°, 105°, or any other suitable angle. 
     In any of the embodiments described above or elsewhere in this specification, the enclosing body can be shaped, dimensioned, or otherwise configured to correspond to the shape and/or size of a facet joint capsule of a healthy facet joint. In any of the embodiments described above or elsewhere in this specification, the enclosing body can be configured to perform the functions of a facet joint capsule of a healthy facet joint. 
     In any of the embodiments described above or elsewhere in this specification, the articulating body can be configured to move superiorly and inferiorly within the enclosing body. In any of the embodiments described above or elsewhere in this specification, the articulating body can be configured to move along an axis parallel or substantially parallel with a superior/inferior axis of a patient. In any of the embodiments described above or elsewhere in this specification, the enclosing body can be configured to restrict movement of the articulating body within the enclosing body such that the articulating body moves only along the axis parallel or substantially parallel with the superior/inferior axis of the patient. 
     In any of the embodiments described above or elsewhere in this specification, the enclosing body can be configured to restrict movement of the articulating body within the enclosing body such that the second articulating surface moves only along an axis parallel or substantially parallel with the superior/inferior axis of the patient. In any of the embodiments described above or elsewhere in this specification, the enclosing body can be configured to restrict movement of the articulating body within the enclosing body such that the articulating body moves only along an axis parallel or substantially parallel with an angle formed by the juxtaposed first articulating surface and second articulating surface. In any of the embodiments described above or elsewhere in this specification, the enclosing body can be configured to restrict movement of the articulating body within the enclosing body such that the second articulating surface moves only along an axis parallel or substantially parallel with an angle formed by the two juxtaposed articulating surfaces. 
     In any of the embodiments described above or elsewhere in this specification, an angle between the transverse anatomic plane and a mean orientation of the second articulating surface can be between 0° and 98°, between 10° and 88°, between 20° and 78°, or any other suitable angle for a facet joint replacement device implanted within the cervical spine. In any of the embodiments described above or elsewhere in this specification, an angle between the transverse anatomic plane and a mean orientation of the second articulating surface can be between 35° and 100°, between 45° and 90°, between 55° and 80°, or any other suitable angle for a facet joint replacement device implanted within the thoracic spine. In any of the embodiments described above or elsewhere in this specification, an angle between the transverse anatomic plane and a mean orientation of the second articulating surface can be between 62° and 106°, between 72° and 96°, between 82° and 86°, or any other suitable angle for a facet joint replacement device implanted within the lumbar spine. In any of the embodiments described above or elsewhere in this specification, the transverse anatomic plane may be referred to as the 0° transverse plane. In any of the embodiments described above or elsewhere in this specification, the foregoing angles between the transverse anatomic plane and a mean orientation of the second articulating surface may be referred to as inclination angles of the second articulating surface within the sagittal anatomic plane. 
     In any of the embodiments described above or elsewhere in this specification, an angle between the sagittal anatomic plane and a mean orientation of the second articulating surface can be between 50° and 116°, between 60° and 106°, between 70° and 96°, or any other suitable angle for a facet joint replacement device implanted within the cervical spine. In any of the embodiments described above or elsewhere in this specification, an angle between the sagittal anatomic plane and a mean orientation of the second articulating surface can be between 65° and 140°, between 75° and 130°, between 85° and 120°, or any other suitable angle for a facet joint replacement device implanted within the thoracic spine. In any of the embodiments described above or elsewhere in this specification, an angle between the sagittal anatomic plane and a mean orientation of the second articulating surface can be between 0° and °  90 , between 5° and 80°, between 15° and 70°, or any other suitable angle for a facet joint replacement device implanted within the lumbar spine. In any of the embodiments described above or elsewhere in this specification, the sagittal anatomic plane may be referred to as the 0° sagittal plane. In any of the embodiments described above or elsewhere in this specification, the foregoing angles between the sagittal anatomic plane and a mean orientation of the second articulating surface may be referred to as inclination angles of the second articulating surface within the transverse anatomic plane. 
     In any of the embodiments described above or elsewhere in this specification, the second articulating surface can be configured to articulate relative to the first articulating surface by moving substantially only parallel to an axis defined by the inclination angles of the second articulating surface within the sagittal and transverse anatomic planes. 
     In any of the embodiments described above or elsewhere in this specification, an angle between the transverse anatomic plane and a mean orientation of the first articulating surface can be between 0° and 98°, between 10° and 88°, between 20° and 78°, or any other suitable angle for a facet joint replacement device implanted within the cervical spine. In any of the embodiments described above or elsewhere in this specification, an angle between the transverse anatomic plane and a mean orientation of the first articulating surface can be between 35° and 100°, between 45° and 90°, between 55° and 80°, or any other suitable angle for a facet joint replacement device implanted within the thoracic spine. In any of the embodiments described above or elsewhere in this specification, an angle between the transverse anatomic plane and a mean orientation of the first articulating surface can be between 62° and 106°, between 72° and 96°, between 82° and 86°, or any other suitable angle for a facet joint replacement device implanted within the lumbar spine. In any of the embodiments described above or elsewhere in this specification, the transverse anatomic plane may be referred to as the 0° transverse plane. In any of the embodiments described above or elsewhere in this specification, the foregoing angles between the transverse anatomic plane and a mean orientation of the first articulating surface may be referred to as inclination angles of the first articulating surface within the sagittal anatomic plane. 
     In any of the embodiments described above or elsewhere in this specification, an angle between the sagittal anatomic plane and a mean orientation of the first articulating surface can be between 50° and 116°, between 60° and 106°, between 70° and 96°, or any other suitable angle for a facet joint replacement device implanted within the cervical spine. In any of the embodiments described above or elsewhere in this specification, an angle between the sagittal anatomic plane and a mean orientation of the first articulating surface can be between 65° and 140°, between 75° and 130°, between 85° and 120°, or any other suitable angle for a facet joint replacement device implanted within the thoracic spine. In any of the embodiments described above or elsewhere in this specification, an angle between the sagittal anatomic plane and a mean orientation of the first articulating surface can be between 0° and °  90 , between 5° and 80°, between 15° and 70°, or any other suitable angle for a facet joint replacement device implanted within the lumbar spine. In any of the embodiments described above or elsewhere in this specification, the sagittal anatomic plane may be referred to as the 0° sagittal plane. In any of the embodiments described above or elsewhere in this specification, the foregoing angles between the sagittal anatomic plane and a mean orientation of the first articulating surface may be referred to as inclination angles of the first articulating surface within the transverse anatomic plane. 
     In any of the embodiments described above or elsewhere in this specification, the first articulating surface can be configured to articulate relative to the second articulating surface by moving substantially only parallel to an axis defined by the inclination angles of the first articulating surface within the sagittal and transverse anatomic planes. 
     In any of the embodiments described above or elsewhere in this specification, the facet joint replacement system can include a fastener configured to be removably received within the facet joint replacement device to constrain movement of the articulating body within the enclosing body. In any of the embodiments described above or elsewhere in this specification, the fastener can be configured to removably received within a first channel of the enclosing body and a second channel of the articulating body. In any of the embodiments described above or elsewhere in this specification, the fastener can contain an externally threaded portion configured to removably secure to complementary threads of one or both of the first channel and the second channel. 
     In any of the embodiments described above or elsewhere in this specification, the facet joint replacement system can include an instrument or device holder having a shaft, a handle positioned at a first end of the shaft, and a fastening head positioned at a second end of the shaft. In any of the embodiments described above or elsewhere in this specification, the fastening head can be configured to be removably received within a first channel of the enclosing body and a second channel of the artilating body. In any of the embodiments described above or elsewhere in this specification, the fastening head can contain an externally threaded portion configured to removably secure to complementary threads of one or both of the first channel and the second channel. 
     In any of the embodiments described above or elsewhere in this specification, the facet joint replacement system can include a plug configured to be received in the enclosing body. In any of the embodiments described above or elsewhere in this specification, the plug can be configured to be received within a channel of the enclosing body. In any of the embodiments described above or elsewhere in this specification, the plug can be configured to be received in a channel of the enclosing body after removal of a fastener from the channel. In any of the embodiments described above or elsewhere in this specification, the plug can be configured to seal the first channel relative to the external environment of the enclosing body. In any of the embodiments described above or elsewhere in this specification, the plug can include complementary threads within the channel of the enclosing body. In any of the embodiments described above or elsewhere in this specification, the plug can be dimensioned to extend through only a portion of the channel of the enclosing body. In any of the embodiments described above or elsewhere in this specification, the plug can be configured to fit flush with an exterior surface of the enclosing body. In any of the embodiments described above or elsewhere in this specification, the plug can be configured to removably couple to the fastening head of the device holder. 
     In any of the embodiments described above or elsewhere in this specification, the facet joint replacement system can include a plug assembly including the plug and a plug insertion section coupled to the plug by a frangible connection. In any of the embodiments described above or elsewhere in this specification, the frangible connection can be configured to break, shear, tear, and/or otherwise separate in response to application of a force to the plug assembly. In any of the embodiments described above or elsewhere in this specification, the frangible connection can be configured to break, shear, tear, and/or otherwise separate in response to application of a force to the plug insertion section. In any of the embodiments described above or elsewhere in this specification, the frangible connection can be configured to break, shear, tear, and/or otherwise separate in response to application of a force to the plug insertion section while the plug is maintained in a fixed position. In any of the embodiments described above or elsewhere in this specification, positioning the plug within the enclosing body can include inserting the plug into the enclosing body using the device holder while the plug assembly is coupled to the device holder. In any of the embodiments described above or elsewhere in this specification, the plug assembly can be configured such that while the plug is positioned within the enclosing body and the plug insertion portion is coupled to the plug, the handle of the device holder can be manipulated to cause the plug insertion section to separate from the plug at the frangible connection. 
     In any of the embodiments described above or elsewhere in this specification, the enclosing body can include an outer shell and a liner. In any of the embodiments described above or elsewhere in this specification, the liner can include ultra-high molecular weight polyethylene. In any of the embodiments described above or elsewhere in this specification, the liner can include Vitamin E impregnated ultra-high molecular weight polyethylene. In any of the embodiments described above or elsewhere in this specification, the liner can include a projection extending inwardly relative to a surrounding area of liner, the projection being shaped and positioned to restrict rotation of the articulating body within the enclosing body. In any of the embodiments described above or elsewhere in this specification, the outer shell can include a main body and a cap configured to secure to the main body. In any of the embodiments described above or elsewhere in this specification, the liner can include a main liner body and a liner cap. In any of the embodiments described above or elsewhere in this specification, the liner cap can be configured to be secured to the liner body. In any of the embodiments described above or elsewhere in this specification, the liner can circumferentially enclose the first articulating surface and the second articulating surface during relative movement between the first articulating surface and the second articulating surface. In any of the embodiments described above or elsewhere in this specification, the liner can enclose a circumferential portion of the articulating body that includes the second articulating surface. 
     In any of the embodiments described above or elsewhere in this specification, the enclosing body can include a retention plate. In any of the embodiments described above or elsewhere in this specification, the retention plate can include an opening positioned so that the first attachment member extends out of the opening of the retention plate. In any of the embodiments described above or elsewhere in this specification, a cross-sectional area of the opening can be less than the cross-sectional area of the articulating body. In any of the embodiments described above or elsewhere in this specification, the retention plate can be coupled to the liner and/or the outer shell of the enclosing body to form the enclosing body. In any of the embodiments described above or elsewhere in this specification, the retention plate can at least partially form a barrier to restrict movement of the articulating element in a superior direction relative to the enclosing body 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1 A  depicts a posterior perspective view of the facet joint replacement device  100  showing interior components in dotted lines. 
         FIG.  1 B  depicts an anterior perspective view of the facet joint replacement device  100 . 
         FIG.  2 A  depicts a posterior perspective view of an enclosing element  102 . 
         FIG.  2 B  depicts a posterior perspective view of an inferior articulating element  104 . 
         FIG.  3 A  depicts an anterior perspective view of the enclosing element  102 . 
         FIG.  3 B  depicts an anterior perspective view of the inferior articulating element  104 . 
         FIG.  4    depicts a partial cross-sectional view of the enclosing element  102  showing a cross-section superior to a superior articulating surface  128 . 
         FIG.  5    depicts a first sagittal view of the facet joint replacement device  100 . 
         FIG.  6    depicts a second sagittal view of the facet joint replacement device  100 . 
         FIG.  7    depicts a cross-sectional view of the facet joint replacement device  100 . 
         FIG.  8    depicts a posterior view of a lumbar motion segment  200 . 
         FIG.  9    depicts a sagittal view of the lumbar motion segment  200 . 
         FIG.  10    depicts a posterior view of the lumbar motion segment  200  with the facet joint replacement device  100  implanted. 
         FIG.  11 A  depicts a sagittal view of the lumbar motion segment  200  with the facet joint replacement device  100  implanted. 
         FIG.  11 B  depicts a sagittal view of the lumbar motion segment  200  with the facet joint replacement device  100  implanted showing components positioned within or obstructed by bone in dotted lines. 
         FIG.  12    depicts a posterior view of the lumbar motion segment  200  having a first facet joint replacement device  100 A and a second facet joint replacement device  100 B implanted bilaterally. 
         FIG.  13    depicts a perspective view of a removable clip  300 . 
         FIG.  14    depicts perspective view of the removable clip  300  secured to the facet joint replacement device  100 . 
         FIG.  15    depicts a perspective view of a removable clip  310 . 
         FIG.  16    depicts a perspective view of the removable clip  310  secured to the facet joint replacement device  100 . 
         FIG.  17    depicts a posterior perspective view of a facet joint replacement device  400  and a fastener  440 . 
         FIG.  18    depicts an exploded view of a facet joint replacement device  500 . 
         FIG.  19    depicts a posterior perspective view of a facet joint replacement device  600 . 
         FIG.  20    depicts a posterior view of the motion segment  200  and a motion segment  201  with a first facet joint replacement device  600 A and a second facet joint replacement device  600 B implanted ipsilaterally. 
         FIG.  21    depicts a perspective view of a removable clip  320 . 
         FIG.  22    depicts a perspective view the removable clip  320  secured to the facet joint replacement device  600 . 
         FIG.  23 A  depicts a top posterior perspective view of a facet joint replacement device  700 . 
         FIG.  23 B  depicts a top anterior perspective view of the facet joint replacement device  700 . 
         FIG.  23 C  depicts a bottom posterior perspective view of the facet joint replacement device  700 . 
         FIG.  23 D  depicts a bottom anterior perspective view of the facet joint replacement device  700 . 
         FIG.  23 E  depicts a posterior view of the facet joint replacement device  700 . 
         FIG.  23 F  depicts an anterior view of the facet joint replacement device  700 . 
         FIG.  23 G  depicts a first sagittal view of a lateral side of the facet joint replacement device  700 . 
         FIG.  23 H  depicts a second sagittal view of a medial side of the facet joint replacement device  700 . 
         FIG.  23 I  depicts a top view of the facet joint replacement device  700 . 
         FIG.  23 J  depicts a bottom view of the facet joint replacement device  700 . 
         FIG.  24 A  depicts a first cross-sectional view of an enclosing element  702 . 
         FIG.  24 B  depicts a second cross-sectional view of the enclosing element  702 . 
         FIG.  25 A  depicts a top posterior perspective view of a main body  707 . 
         FIG.  25 B  depicts a top anterior perspective view of the main body  707 . 
         FIG.  25 C  depicts a bottom posterior perspective view of the main body  707 . 
         FIG.  25 D  depicts a bottom anterior perspective view of the main body  707 . 
         FIG.  25 E  depicts a posterior view of main body  707 . 
         FIG.  25 F  depicts an anterior view of the main body  707 . 
         FIG.  25 G  depicts a first sagittal view of a lateral side of the main body  707 . 
         FIG.  25 H  depicts a second sagittal view of a medial side of the main body  707 . 
         FIG.  25 I  depicts a top view of the main body  707 . 
         FIG.  25 J  depicts a bottom view of the main body  707 . 
         FIG.  25 K  depicts a cross-sectional view of the main body  707 . 
         FIG.  25 L  depicts a first perspective view of a cross-section of the main body  707 . 
         FIG.  25 M  depicts a second perspective view of a cross-section of the main body  707 . 
         FIG.  26 A  depicts a first perspective view of a cap  709 . 
         FIG.  26 B  depicts a second perspective view of the cap  709 . 
         FIG.  27 A  depicts a top posterior perspective view of an articulating element  704 . 
         FIG.  27 B  depicts a top anterior perspective view of the articulating element  704 . 
         FIG.  27 C  depicts a bottom posterior perspective view of the articulating element  704 . 
         FIG.  27 D  depicts a bottom anterior perspective view of the articulating element  704 . 
         FIG.  27 E  depicts a posterior view of the articulating element  704 . 
         FIG.  27 F  depicts an anterior view of the articulating element  704 . 
         FIG.  27 G  depicts a first sagittal view of a lateral side of the articulating element  704 . 
         FIG.  27 H  depicts a second sagittal view of a medial side of the articulating element  704 . 
         FIG.  27 I  depicts a top view of the articulating element  704 . 
         FIG.  27 J  depicts a bottom view of the articulating element  704 . 
         FIG.  27 K  depicts a cross-sectional view of the articulating element  704 . 
         FIG.  28    is an exploded view of a facet joint replacement system including the facet joint replacement device  700  and a fastener  740 . 
         FIG.  29 A  depicts a posterior view of the facet joint replacement device  700 . 
         FIG.  29 B  depicts a posterior-medial view of the facet joint replacement device  700 . 
         FIG.  29 C  depicts a posterior-medial view of the facet joint replacement device  700 . 
         FIG.  29 D  depicts a posterior-medial view of the facet joint replacement device  700 . 
         FIG.  29 E  depicts a posterior-medial cross-sectional view of the facet joint replacement device. 
         FIG.  29 F  depicts a posterior-medial cross-sectional view of the facet joint replacement device. 
         FIG.  29 G  depicts a posterior-medial cross-sectional view of the facet joint replacement device. 
         FIG.  30 A  depicts a posterior view of the facet joint replacement device  700 . 
         FIG.  30 B  depicts a sagittal view showing a lateral side of the facet joint replacement device  700 . 
         FIG.  30 C  shows a cross-sectional view of the facet joint replacement device  700 . 
         FIG.  31 A  depicts a cross-sectional view of the facet joint replacement device  700  showing the cap  709  separated from the main body  707 . 
         FIG.  31 B  depicts a cross-sectional view showing the cap  709  partially engaging the main body  707 . 
         FIG.  31 C  depicts a cross-sectional view of the facet joint replacement device  700  showing the cap  709  coupled to the main body  707 . 
         FIG.  31 D  depicts an exploded perspective view of the facet joint replacement device  700  showing the cap  709  separated from the main body  707 . 
         FIG.  31 E  depicts a perspective view of the facet joint replacement device  700  showing the cap  709  coupled to the main body  707 . 
         FIG.  31 F  depicts a cross-sectional perspective view of the facet joint replacement device  700  showing the cap  709  separated from the main body  707 . 
         FIG.  31 G  depicts a cross-sectional perspective view of the facet joint replacement device  700  showing the cap  709  coupled to the main body  707 . 
         FIG.  32 A  depicts a top perspective view of the fastener  740 . 
         FIG.  32 B  depicts a bottom perspective view of the fastener  740 . 
         FIG.  32 C  depicts a front view of the fastener  740 . 
         FIG.  32 D  depicts a cross-sectional view showing the fastener  740  positioned within the channels  744  and  746  of the enclosing body  706  and articulating element  718 . 
         FIG.  32 E  depicts a perspective cross-sectional view showing the fastener  740  positioned within the channels  744  and  746  of the enclosing body  706  and articulating element  718 . 
         FIG.  33 A  depicts a top perspective view of the plug  780 . 
         FIG.  33 B  depicts a bottom perspective view of the plug  780 . 
         FIG.  33 C  depicts a cross-sectional view showing the plug  780  positioned within the channel  744 . 
         FIG.  33 D  depicts a perspective cross-sectional view showing the plug  780  positioned within the channel  744 . 
         FIG.  34 A  depicts a posterior view of the lumbar motion segment  200  with the facet joint replacement device  700  implanted. 
         FIG.  34 B  depicts a sagittal view of the lumbar motion segment  200  with the facet joint replacement device  700  implanted. 
         FIG.  34 C  depicts a bottom view of the lumbar motion segment  200  with the facet joint replacement device  700  implanted. 
         FIG.  34 D  depicts a perspective view of the lumbar motion segment  200  with the facet joint replacement device  700  implanted. 
         FIG.  34 E  depicts a sagittal view of the lumbar motion segment  200  with the facet joint replacement device  700  implanted showing the bone as transparent to illustrate components positioned within or obstructed by bone. 
         FIG.  34 F  depicts a posterior view of the lumbar motion segment  200  with the facet joint replacement device  700  implanted showing the bone as transparent to illustrate components positioned within or obstructed by bone. 
         FIG.  34 G  depicts a bottom view of the lumbar motion segment  200  with the facet joint replacement device  700  implanted showing the bone as transparent to illustrate components positioned within or obstructed by bone. 
         FIG.  35    depicts a bottom view of the facet joint replacement device  700 . 
         FIG.  36 A  depicts a top posterior perspective view of a facet joint replacement device  900 . 
         FIG.  36 B  depicts a top anterior perspective view of the facet joint replacement device  900 . 
         FIG.  36 C  depicts a bottom posterior perspective view of the facet joint replacement device  900 . 
         FIG.  36 D  depicts a bottom medial perspective view of the facet joint replacement device  900 . 
         FIG.  36 E  depicts a posterior view of the facet joint replacement device  900 . 
         FIG.  36 F  depicts an anterior view of the facet joint replacement device  900 . 
         FIG.  36 G  depicts a first sagittal view of a lateral side of the facet joint replacement device  900 . 
         FIG.  36 H  depicts a second sagittal view of a medial side of the facet joint replacement device  900 . 
         FIG.  36 I  depicts a top view of the facet joint replacement device  900 . 
         FIG.  36 J  depicts a bottom view of the facet joint replacement device  900 . 
         FIG.  37 A  depicts a posterior longitudinal cross-sectional view of an enclosing element  902 . 
         FIG.  37 B  depicts an anterior, longitudinal cross-sectional view of the enclosing element  902 . 
         FIG.  37 C  depicts a top view of the enclosing element  902 . 
         FIG.  37 D  depicts a bottom cross-sectional view of the enclosing element  902 . 
         FIG.  37 E  depicts a first perspective view of a cross-section of the enclosing element  902 . 
         FIG.  37 F  depicts a second perspective view of a cross-section of the enclosing element  902 . 
         FIG.  37 G  depicts a fourth cross-sectional view of the enclosing element  902 . 
         FIG.  37 H  depicts a third perspective view of a cross-section of the enclosing element  902 . 
         FIG.  37 I  depicts a fourth perspective view of a cross-section of the enclosing element  902 . 
         FIG.  38 A  depicts a top posterior perspective view of an articulating element  904 . 
         FIG.  38 B  depicts a top anterior perspective view of the articulating element  904 . 
         FIG.  38 C  depicts a bottom posterior perspective view of the articulating element  904 . 
         FIG.  38 D  depicts a bottom medial perspective view of the articulating element  904 . 
         FIG.  38 E  depicts a posterior view of the articulating element  904 . 
         FIG.  38 F  depicts an anterior view of the articulating element  904 . 
         FIG.  38 G  depicts a first sagittal view of a lateral side of the articulating element  904 . 
         FIG.  38 H  depicts a second sagittal view of a medial side of the articulating element  904 . 
         FIG.  38 I  depicts a top view of the articulating element  904 . 
         FIG.  38 J  depicts a bottom view of the articulating element  904 . 
         FIG.  38 K  depicts a cross-sectional view of the articulating element  904 . 
         FIG.  39    is an exploded view of the facet joint replacement device  900 . 
         FIG.  40 A  depicts a posterior-medial cross-sectional view of the facet joint replacement device  900 . 
         FIG.  40 B  depicts a posterior-medial cross-sectional view of the facet joint replacement device  900 . 
         FIG.  40 C  depicts a posterior-medial cross-sectional view of the facet joint replacement device  900 . 
         FIG.  41 A  depicts a top perspective of a retention plate  917 . 
         FIG.  41 B  depicts a bottom perspective view of the retention plate  917 . 
         FIG.  41 C  depicts a front view of the retention plate  917 . 
         FIG.  42 A  depicts a perspective view of a device holder  1040 . 
         FIG.  42 B  depicts a front view of the device holder  1040 . 
         FIG.  42 C  depicts a side view of the device holder  1040 . 
         FIG.  42 D  depicts a top perspective enlarged view of a portion of the device holder  1040 . 
         FIG.  42 E  depicts a bottom perspective enlarged view of a portion of the device holder  1040 . 
         FIG.  42 F  depicts a perspective view of the device holder  1040  coupled to the facet joint replacement device  900 . 
         FIG.  42 G  depicts an enlarged cross-sectional view of a portion of the device holder  1040  coupled to the facet joint replacement device  900 . 
         FIG.  43 A  depicts a top perspective view of a plug assembly  1020 . 
         FIG.  43 B  depicts a bottom perspective view of the plug assembly  1020 . 
         FIG.  43 C  depicts a first enlarged cross-sectional view of the plug assembly  1020 . 
         FIG.  43 D  depicts a second enlarged cross-sectional view of the plug assembly  1020  showing the plug assembly  1020  separated into two pieces. 
         FIG.  44 A  depicts a perspective view of the device holder  1040  coupled to the plug assembly  1020 . 
         FIG.  44 B  depicts an enlarged cross-sectional view showing a portion of the device holder  1040  coupled to the plug assembly  1020 . 
         FIG.  44 C  is a front view showing the device holder  1040  coupled to a plug insertion section  1022  after separation of the plug insertion section  1022  from a plug  980 . 
         FIG.  45 A  depicts a posterior view of a facet joint replacement device  900 A. 
         FIG.  45 B  depicts a posterior view of an articulating element  904 A. 
         FIG.  45 C  depicts a posterior view of a facet joint replacement device  900 B. 
         FIG.  45 D  depicts a posterior view of an articulating element  904 B. 
         FIG.  45 E  depicts a posterior view of a facet joint replacement device  900 C. 
         FIG.  45 F  depicts a posterior view of an articulating element  904 C. 
         FIG.  46    depicts a perspective view of an embodiment of an outer shell  950 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Methods, systems, and apparatuses are provided in certain embodiments of the present invention to replace a dysfunctional facet joint. In some embodiments a facet joint replacement device is provided. The facet joint replacement device can be configured to replace a facet joint that has been partially or fully resected. Following replacement, the facet joint replacement device can be configured to perform the function of a facet joint within a spinal motion segment. For example, the facet joint replacement device can include one or more components configured to perform the functions of a superior articular process, and inferior articular process, and/or a facet joint capsule. In some embodiments, the facet joint replacement device can include an enclosing element and one or more interior components positioned within an inner cavity of the enclosing element. The interior components can be configured to move within the enclosing element to facilitate movements of a spinal motion segment that simulate the movements allowed by a healthy facet joint in the human body. For example, the facet joint replacement device can allow for limited posterior/anterior motion, limited medial/lateral motion, and/or limited superior/inferior motion. The facet joint replacement device can also limit relative rotation and translation of adjacent vertebrae. For example, in some embodiments, the inner cavity of the enclosing element can be shaped and/or dimensioned to limit relative movement of the interior components within the enclosing element in at least one direction. In some embodiments, the enclosing element is shaped and/or dimensioned to limit relative movement in similar directions to a healthy facet joint capsule. 
     In some embodiments, the enclosing element can include a surface configured to simulate a superior articular surface of a healthy facet joint. In some embodiments, at least one of the internal components can include a surface configured to simulate an inferior articular surface that complements of a healthy facet joint. The enclosing body can be configured to provide resistance to or otherwise limit relative disassociation and/or rotation between the surfaces configured to simulate the superior articular surface and the inferior articular surface. The enclosing body can also maintain an intra-articular environment by encapsulating the surfaces configured to simulate the superior articular surface and the inferior articular surface. For example, the enclosing cylinder can act as a physical barrier to fibrosis at the surfaces configured to simulate the superior articular surface and the inferior articular surface. The enclosing cylinder can also act as a physical barrier to prevent friction wear to the adjacent anatomy due to relative movement between the surfaces configured to simulate the superior articular surface and the inferior articular surface. 
     In some embodiments, a body of the enclosing element can be shaped to conform to the shape of superior and inferior articular processes and a pars interarticularis of a healthy vertebral body. The shape of the enclosing element can be configured to support axial loading in a similar manner as healthy articular processes. 
     In some embodiments, at least some of the components of the facet joint replacement device can be designed such that assembly of the facet joint replacement device can be performed outside of the body. Such a facet joint replacement device can facilitate ease of implantation, as well as minimally invasive techniques. 
       FIGS.  1 A- 7    depict a facet joint replacement device  100  according to one embodiment. The terms superior, inferior, anterior, posterior, medial, and lateral, when describing portions of the devices herein, refer to portions of the device as they are intended to be oriented with respect to the human spine.  FIG.  1 A  depicts a posterior perspective view of the facet joint replacement device  100  showing interior components in dotted lines.  FIG.  1 A  also includes three-dimensional coordinate axes indicating the superior (“S”), inferior (“I”), anterior (“A”), posterior (“P”), medial (“M”), and lateral (“L”) directions. As shown in the three-dimensional coordinate axes in  FIG.  1 A , the posterior direction P is generally pointing out of the page and the anterior direction A is generally pointing into the page. The facet joint replacement device  100  includes an enclosing element  102  and an inferior articulating element  104  positioned at least partially within the enclosing element  102 . The articulating element  104  is referred to as an inferior articulating element because it provides a generally inferiorly facing articulating surface to engage a corresponding generally superiorly facing articulating surface on the enclosing element  102 , as described further below. 
     The enclosing element  102  includes an enclosing body  106  and an inferior attachment member  112 . The enclosing body  106  can have a generally arcuate shape configured to correspond to the shape of a pars interarticularis of a vertebra. The enclosing body  106  includes a superior end  108  and an inferior end  110 . The inferior attachment member  112  extends laterally from the enclosing body  106  at a segment of the enclosing body adjacent to the inferior end  110 . The enclosing body  106  further include an inner cavity  114  (shown in  FIG.  4   ) defined by an interior surface of the enclosing body  106  and an opening  116  (shown in  FIG.  2 A ) at the superior end  108 . A portion of the interior surface of the enclosing body  106  can be shaped to form a superior articulating surface  128  (shown in  FIG.  4   ). In some embodiments, the enclosing body  106  is configured to protect the surrounding anatomy from friction, damage, or infection due to the movement of components, including the inferior articulating surface  126  and superior articulating surface  128  in the interior of the enclosing body  106 , for example, by acting as a physical barrier. For example, the enclosing body  106  can protect an adjacent thecal sac and adjacent nerve roots from involvement with the articulating surfaces  126  and  128  during relative movement between the articulating surfaces  126  and  128 . In some embodiments, the enclosing body  106  is configured to protect the components within the interior of the enclosing body  106  from damage, wear, or fibrosis due to the surrounding anatomy, for example, by acting as a physical barrier. 
     The inferior articulating element  104  includes an articulating body  118  and a superior attachment member  120 . The articulating body  118  is at least partially positioned within and configured to move within the inner cavity  114  of the enclosing body  106 . The inferior articulating body  118  has a superior end  122  and an inferior end  124 . The superior attachment member  120  extends superior to the superior end  122  of the articulating body  118 . In some embodiments, the superior attachment member  120  extends through the opening  116 . In some embodiments, a portion of the articulating body  118  extends superior to or in alignment with the opening  116 . The inferior end  124  of the articulating body  118  forms an inferior articulating surface  126 . 
     The superior attachment member  120  and inferior attachment member  112  can be shaped and/or dimensioned to facilitate securement of the facet joint replacement device  100  to the spine. As shown in  FIG.  1 A , the superior attachment member  120  and inferior attachment member  112  can each be a rod. However, the superior attachment member  120  and inferior attachment member  112  can be any shape suitable for fixation directly or indirectly to a vertebral body. 
     In some embodiments, the enclosing element  102  and/or the inferior articulating element  104  can consist of or consist partially of one or more metals or metal alloys. For example, the enclosing element  102  and/or articulating element  104  can consist of cobalt-chromium, titanium, titanium-based alloys, or any other suitable metals or metal alloys. In some embodiments, the enclosing element  102  and/or inferior element  104  can be ceramic or partially ceramic. In some embodiments, the enclosing element  102  and/or inferior element  104  can include super-hard ceramics. 
       FIG.  1 B  depicts an anterior perspective view of the facet joint replacement device  100 .  FIG.  1 B  also includes three-dimensional coordinate axes indicating the superior (“S”), inferior (“I”), anterior (“A”), posterior (“P”), medial (“M”), and lateral (“L”) directions. As shown in the three-dimensional coordinate axes of  FIG.  1 B , the anterior direction A is generally pointing out of the page and the posterior direction P is generally pointing into the page. As shown in  FIG.  1 B , the inferior articulating surface  124  can be configured to face at least partially in an anterior direction, as well as in a generally inferior direction and a generally lateral direction. 
       FIG.  1 B  also shows an axis  103  extending through a center point of the inferior articulating surface and an axis  105  extending through a long axis of the attachment member  120 . Both the axis  105  and the axis  103  have superior-inferior, lateral-medial, and posterior-anterior components. 
       FIGS.  2 A and  2 B  depicts a posterior perspective view of the enclosing element  102  and a posterior perspective view of the inferior articulating element  104 , respectively.  FIG.  2 A  shows the opening  116  through which a portion of the articulating body  118  can extend or align with when positioned within the enclosing body  106  of the enclosing element  102 . 
       FIGS.  3 A and  3 B  depict an anterior perspective view of the enclosing element  104  and an anterior perspective view of the inferior articulating element  104 , respectively. As illustrated in  FIG.  3 B , the inferior articulating surface  126  can be ellipsoid or generally elliptical. The inferior articulating surface  126  can also be convex or at least partially convex. The inferior articulating surface  126  can be shaped and/or dimensioned to correspond to the shape, size, and/or convexity of an articular surface of a healthy inferior articular process. 
       FIG.  4    depicts a partial cross-sectional view of the enclosing element  102  showing a cross-section superior to the superior articulating surface  128 .  FIG.  4    shows the inner cavity  114  defined by the interior surface of the enclosing body  106  and the superior articulating surface  128 . As illustrated in  FIG.  4   , superior articulating surface  128  can be defined by a section of the interior surface of the enclosing body  106 . The superior articulating surface  128  can be ellipsoid or generally elliptical. The superior articulating surface  128  can also be concave or at least partially concave. The superior articulating surface  128  can be shaped/and or dimensioned to correspond to the shape, size, and/or concavity of an articular surface of a healthy superior articular process. 
     While the inferior articulating surface  126  and superior articulating surface  128  are shown as elliptical in  FIGS.  3 B and  4   , any suitable complementary surface shapes can be used. In some embodiments, the inferior articulating surface  126  and superior articulating surface  128  are circular or generally circular, oval or generally oval, rounded, polygonal, oblong, symmetric, asymmetric, or any other suitable shape. In some embodiments, the inferior articulating surface  126  and superior articulating surface  128  can be shaped such that force is applied symmetrically to the superior articulating  128  when the inferior articulating element  126  contacts or otherwise applies a force upon the superior articulating surface  126 . 
     As described further herein, the articulating body  118  is configured to move within the enclosing body  106  in at least one direction. When the superior attachment member  120  is secured to a superior vertebral body and the inferior attachment member  112  is secured to an inferior vertebral body, movement between the superior and inferior vertebral bodies can cause movement of the superior attachment member  120  with respect to the position of the enclosing body  106  resulting from the inferior attachment member  112  being secured to the inferior vertebral body. Movement of the superior attachment member  120  with respect to the enclosing body  106  causes movement of the articulating body  118  within the enclosing body  106  generally along the inner wall of the enclosing body. Referring again to  FIG.  1 B , the superior attachment member  120  is configured to move along axis  105  towards and away from the enclosing body  106 . When the superior attachment member  120  moves towards the enclosing body  106  along the axis  105 , the superior attachment member  120  moves along the axis  105  in a medial, anterior, and inferior direction. When the superior attachment member  120  moves away from the enclosing body  106  along the axis  105 , the superior attachment member  120  moves along the axis  105  in a lateral, posterior, and superior direction. The superior end  122  of the articulating body  118  moves along the axis  105  in the same manner when the superior attachment member  120  moves along the axis  105 . Although relative movement of the superior attachment member  120  towards and away from the enclosing body  106  is discussed, one of skill in the art would understand that movement between the enclosing body  106  and superior attachment member  120  could be described as movement of the enclosing body  106  towards or away from the superior attachment member  120  or movement of the enclosing body  106  and superior attachment member  120  towards or away from each other. 
     Movement of the superior attachment member  120  with respect to the enclosing body  106  causes movement of the inferior articulating surface  126  along the axis  103  towards and away from the superior articulating surface  128 . The inferior articulating surface  126  moves towards the superior articulating surface  128  along the axis  103  when the superior attachment member  120  moves towards the enclosing body  106 , and the inferior articulating surface  126  moves away from the superior articulating surface  128  when the superior attachment member  120  moves away from the enclosing body  106 . When the inferior articulating surface  126  moves away from the superior articulating surface  128  along the axis  103 , the inferior articulating surface moves along the axis  103  in a superior, posterior, and medial direction. When the inferior articulating surface  126  moves towards the superior articulating surface  128  along the axis  103 , the inferior articulating surface moves along the axis  103  in an inferior, anterior, and lateral direction. Although relative movement of the inferior articulating surface  126  towards and away from the superior articulating surface  128  is discussed, one of skill in the art would understand that movement between the inferior articulating surface  126  and the superior articulating surface  128  could be described as movement of the superior articulating surface  128  towards or away from the inferior articulating surface  126  or movement of the inferior articulating surface  126  and the superior articulating surface  128  towards or away from each other. In some embodiments, the axis  103  extends through a center point of the superior articulating surface  128 . In some embodiments, the axis  103  extends transverse to a tangent of a center line of the inferior articulating surface  126 . The axis  103  can represent the direction of relative movement between the articular surfaces of a healthy facet joint. 
     In some embodiments, the enclosing body  106  acts to limit relative movement between the inferior articulating surface  126  and the superior articulating surface  128  along the axis  103 . In some embodiments, the enclosing body  106  acts to limit relative movement of the inferior articling surface  126  and superior articulating surface  128  perpendicular to the axis  103 . 
     When the articulating body  118  moves within the enclosing body  106 , the inferior articulating surface  126  can contact the superior articulating surface  128 . In some embodiments, the enclosing body  106  and inferior articulating body  118  are configured such that a maximum distance between a center point of the inferior articulating surface  126  and the superior articulating surface  128  is 0.5 mm, 1.0 mm, 1.5 mm, 1.75 mm, 2.0 mm, 2.25 mm, 2.5 mm, 3.0 mm, 3.5 mm, 4.0 mm, 5.0 mm, less than 2.0 mm, less than 3.0 mm, less than 4.0 mm, between 1.0 mm and 3.0 mm, between 1.0 mm and 2.0 mm, between 2.0 mm and 3.0 mm, between 1.5 mm and 2.5 mm, or between 1.75 mm and 2.25 mm. In some embodiments, the superior articulating surface  128  is shaped and/or dimensioned to receive the inferior articulating surface  126 . As shown in  FIG.  4   , the enclosing body  106  includes a solid portion  130  between the superior articulating surface  128  and the inferior attachment member  112 . In some embodiments, the solid portion  130  of the enclosing body  106  can have a depth dimensioned for receiving an axial load supplied by the articulating body  118  to the inferior articulating surface  126  due to movement of the articulating body  118  within the enclosing body  106 . 
       FIGS.  5  and  6    show a first sagittal view showing a lateral side of the facet joint replacement device  100  and a second sagittal view showing a medial side of the facet joint replacement device  100 , respectively.  FIG.  7    shows a cross-sectional view of the facet joint replacement device  100  taken along line  7 - 7  as show in  FIG.  1 A . As shown in  FIG.  7   , the interior surface of the enclosing body  106  includes a plurality of internal corners or grooves  130   a ,  130   b , and  130   b , each forming angle that corresponds to one of a plurality of external corners or edges  132  of the articulating body  118 . Groove  130   b  is generally positioned within the posterior side of the facet joint replacement device  100 . A linear portion extends between groove  130   a  and groove  130   b . A second linear section extends between groove  130   c  and groove  130   b . An arcuate section extends between groove  130   a  and groove  130   c . The arcuate section between groove  130   a  and groove  130   c  is generally positioned within the anterior side of the facet joint replacement device  100 . The grooves  130  can extend along one or more portions of the interior surface of the enclosing body  106 . In some embodiments, the grooves  130  extend along a length of the interior surface of the enclosing body  106  from the superior end  108  to the superior articulating surface  128 . The edges  132  can extend along one or more portions of the outer surface of the articulating body  118 . In some embodiments, the edges  132  can extend along a length of the outer surface of the articulating body  118  between the superior end  122  to the inferior articulating surface  126 . The grooves  130  of the enclosing body  106  can be configured to engage the edges  132  of the articulating body  118  to prevent relative rotation of the articulating body  118  within the enclosing body  106 . The enclosing body  106  and articulating body  118  can be shaped and dimensioned to allow for relative axial movement between the inferior articulating surface  126  and the superior articulating surface  128  along the axis  103 . 
     While three grooves  130  and three edges  132  are shown in  FIG.  7   , any number of grooves and edges may be utilized to prevent relative rotation of the articulating body  118  within the enclosing body  106 . One of skill in the art would recognize that the cross-sections of the inner wall of the enclosing body  106  and the outer surface of the articulating body  118  could be any corresponding non-circular cross-sections suitable to prevent relative rotation and allow for relative translation along the length of the enclosing body  106 . For example, in some embodiments, the inner wall of the enclosing body  106  and the outer surface of the articulating body  118  can each have an oval cross-section. 
     As described herein, the components of the facet joint replacement device  100  can be shaped and/or dimensioned to correspond to the anatomy of a healthy facet joint and related spinal motion segment. While lumbar facet joints are shown and described herein, applications of the facet joint replacement device  100  are not limited to the lumbar spine. In some embodiments, the facet joint replacement device  100  can be shaped and/or dimensioned to correspond to the anatomy of the thoracic spine. In some embodiments, a vertical distance between the superior end  108  of the enclosing body and the inferior end  110  of the enclosing body is between 20 mm to 44 mm, between 24 mm to 40 mm, between 28 mm and 36 mm, or between 30 mm and 34 mm. In some embodiments a vertical distance between the superior end  108  of the enclosing body and the inferior end  110  of the enclosing body is 28 mm, 29 mm, 30 mm, 31 mm, 32 mm, 33 mm, 34 mm, 35 mm, or 36 mm. 
     In some embodiments, one or both of the superior articular surface  128  and inferior articular surface  126  can have a major axis length of 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, 16 mm, 17 mm, 18 mm, between 10 mm to 25 mm, between 9 to 14 mm, between 10 to 14 mm, or between 12 mm to 14 mm. In some embodiments, one or both of the superior articular surface  128  and inferior articular surface  126  can have a minor axis length of 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, 16 mm, 17 mm, 18 mm, between 8 mm to 25 mm, between 8 mm to 14 mm, between 9 mm to 14 mm, or between 12 mm to 14 mm. 
     In some embodiments, the superior articulating surface  128  can be oriented at an angle of between 75° to 95° or between 55° to 85° from a transverse anatomic plane. In some embodiments, the superior articulating surface  128  can be oriented at an angle of between −100° to −150° or between −65° to −85° from a sagittal anatomic plane. In some embodiments, the inferior articulating surface  128  can be oriented at an angle of between 60° to 90° or between 55° to 85° from a transverse anatomic plane. In some embodiments, the superior articulating surface  128  can be oriented at an angle of between −65° to −165° or between −65° to −145° from a sagittal anatomic plane. 
     In some embodiments, an angle between the axis  103  and axis  105  can be 60°, 70°, 80°, 90°, 100°, 110°, 120°, 130°, between 60° and 130°, between 70° and 120°, between 80° and 110°, between 90° and 100°, between 60° and 80°, between 80° and 100°, or between 100°, and 120°. 
     In some embodiments, an angle between a plane extending through the center point of the inferior articulating surface  126  and a plane defined by the superior end  122  of the articulating body  118  can be 60°, 70°, 80°, 90°, 100°, 110°, 120°, 130°, between 60° and 130°, between 70° and 120°, between 80° and 110°, between 90° and 100°, between 60° and 80°, between 80° and 100°, or between 100°, and 120°. 
     In some embodiments, one or both of the superior attachment member  120  and the inferior attachment member  112  can have a diameter of 1 mm, 2 mm, 3 mm, 4 mm, 4.5 mm, 5 mm, 5.5 mm, 6 mm, 6.5 mm, 7 mm, 8 mm, 9 mm, 10 mm, between 2 mm to 8 mm, between 4 mm to 6 mm, between 5 mm to 7 mm, or between 5 mm to 6 mm. In some embodiments, one or both of the superior attachment member  120  and the inferior attachment member  112  can have a length of 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, between 2 mm to 8 mm, between 4 mm to 6 mm, between 5 mm to 10 mm, between 10 mm to 15 mm, between 15 mm to 20 mm, between 20 mm to 25 mm, between 25 mm to 30 mm, between 15 mm to 30 mm, or less than 15 mm. 
     In some embodiments, a thickness of the solid portion  130  between the superior articulating surface  128  and an inferior most point of the enclosing body  106  along the axis  103  can be 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm between 8 mm to 25 mm, between 6 mm to 14 mm, or between 8 mm to 12 mm. 
     In some embodiments, the widest section of the enclosing body  106  is at the superior articulating surface  128 . The enclosing body  106  can include an inflection point at the superior articulating surface  128 . In some embodiments, the enclosing body  106  bows medially between the superior articulating surface  128  and the superior end  108  of the enclosing body  106 . In some embodiments, the articulating body  118  bows medially between the inferior articulating surface  128  and the superior end  122  of the articulating body  118 . 
       FIGS.  8  and  9    depict a posterior view and a sagittal view, respectively, of a lumbar motion segment  200  including a superior vertebra  205 , an inferior vertebra  210 , and an intervening disc  215 . The superior vertebra  205  includes a superior articular process  220 , an inferior articular process  225 , and a pars interarticularis  230  extending between the superior articular process  220  and the inferior articular process  225 . The pars interarticularis  230  is positioned between lamina  235  and pedicle  240 . The pedicle  242  is also shown. A superior articular process  245  of the inferior vertebra  210  is also shown. An articular surface  250  of the superior articular process  245  and an articular surface  255  of the inferior articular process  225  align to form facet joint  260 , which is encapsulated by a facet joint capsule (not shown). A sagittal inclination angle of the lumbar facet joint can range between 82° to 86°. As shown in  FIG.  8   , the facet joint  260  is located medial to transverse process  265  and lateral to spinous process  270 . The facet joint is axially offset from the midline of the spine by between 15° to 70° degrees, dependent on the lumbar level, with more inferior lumbar segments have greater axial offset angles. 
       FIGS.  10  and  11 A  depict a posterior view and a sagittal view, respectively, of a lumbar motion segment  200  with the facet joint replacement device  100  implanted. The superior attachment member  120  is affixed to the pedicle  240  of a superior vertebra or superior vertebral body  205  by a fastener  274 . The inferior attachment member  112  is affixed to the pedicle  242  of an interior vertebra or inferior vertebral body  210  by a fastener  276 . As shown in  FIGS.  10  and  11 A , the fasteners  274  and  276  each include a tulip head bone screw and a top loading set screw.  FIG.  11 B  shows the positioning of the tulip head bone screws of fasteners  274  and  276  within pedicles  240  and  242  in dotted lines. 
       FIGS.  10  and  11 A  show a unilateral implantation of a facet joint replacement device  100 . One of skill in the art would understand that a facet joint replacement device, such as facet joint replacement device  100 , can be implanted on either lateral side of a motion segment, or two facet joint replacement devices can be implanted bilaterally, one on each side of a particular motion segment.  FIG.  12    depicts a posterior view of the lumbar motion segment  200  having a first facet joint replacement device  100 A positioned on a first lateral side of the lumbar motion segment  200  and a second facet joint replacement device  100 B positioned on a second lateral side of the lumber motion segment  200 . 
     In some embodiments, a method for implanting facet joint replacement device  100  into a patient begins with the administration of general endotracheal anesthesia. Following the administration of anesthesia, the patient is placed into a prone position and intraoperative fluoroscopy is used to identify a desired location for making a skin incision for implanting the facet joint replacement device  100 . After the desired location is selected, a midline lumbar-sacral incision is made at the desired location, and subperiosteal dissection is utilized to expose a desired lamina, facet joint, and entry points to cannulate the ipsilateral pedicles of the superior and inferior vertebral bodies associated with the facet joint to be replaced. In some alternative embodiments, minimally invasive surgical techniques can be employed for exposure of the desired lamina, facet joint, and entry points to cannulate the ipsilateral pedicles. After exposure of the desired structures, intraoperative fluoroscopy is utilized to confirm desired levels of exposure. After the desired levels of exposure are confirmed, a self-retaining retractor system is placed to maintain the desired level of exposure. 
     After the retractor system is in place, removal of one or more sections of the facet joint and surrounding bone is performed. In some embodiments, the lamina or portion of the lamina in the motion region to be treated is removed. Removal can be performed using bone biters, angled curets, and/or bone punches. In some embodiments, a ligamentum flavum or a portion of the ligamentum flavum in the motion segment to be treated is removed. Removal of the ligamentum flavum can be performed using bone punches. The facet joint or a portion of the facet joint to be treated is also removed. Removal of the facet joint can be performed using a high speed drill, bone biters, and/or bone punches. After removal of the facet joint to be treated, further decompression of the lateral recess can be performed and adjacent nerve roots can be identified. Additional bone may be removed as necessary to prevent mechanical compression of the nerve roots. 
     Following removal of the desired bone, the pedicles of the superior vertebral body and inferior vertebral body of the motion segment to be treated and desired points of entry to cannulate the pedicles are identified, for example, using intraoperative fluoroscopy. A high speed drill or bone awl is then used to perforate the cortical bone overlying the optimal entry points to cannulate each of the pedicles. The pedicles are then probed and tapped under fluoroscopic guidance. Tulip head bone screws, such as the tulip head bone screws of fasteners  274  and  276 , are then screwed into the previously tapped pedicles. Additional fixation augmentors, such as methylmethacrylate, can also be used. In some embodiments, a decision to use additional fixation augmentors is made based on apparent bone quality at the time of bone screw insertion. Methylmethacrylate or other fixation augmentors can be placed within the cannulated pedicle prior to placement of the bone screw, for example, to improve the fixation of the bone screw within the implanted pedicle bone. 
     After fixation of the bone screws to the superior and inferior vertebral bodies, the superior attachment member  120  can be placed within a receiving portion of the tulip head portion of the bone screw in the superior vertebral body, and the inferior attachment member  112  can be placed within a receiving portion of the tulip head portion of the bone screw in the inferior vertebral body. After the superior attachment member  120  and inferior attachment member  112  are received within the tulip head portions of the implanted bone screws, the superior attachment member  120  and inferior attachment member  112  can be secured to the bone screws by fixation of top loading set screws to each of the tulip head portions of the implanted bone screws. 
     In some embodiments, after ensuring that the implanted bone screws are in proper position and secure, but before the attachment members  120  and  112  are placed into the bone screws, distraction or compression can be applied between the implanted bone screws to address any asymmetric loss of the disc space height or malalignment. 
     In some embodiments, facet joint replacement devices may be available in a plurality of different sizes. In such embodiments, after implantation of the tulip head bone screws into the superior and inferior vertebral bodies, a distance is measured between the tulips head portions of the bone screws and a facet joint replacement device can be selected based on the distance measured between the tulip head portions of the bone screws, for example, so that the superior and inferior attachment members of the facet joint replacement device can be securely engaged with the tulip head portions of the implanted bone screws. 
     In some embodiments, facet joint replacement devices may be available with inferior articulating surfaces and superior articulating surfaces having a plurality of different angular orientations with respect to the sagittal and transverse anatomic planes, as described further herein. In such embodiments, after implantation of the tulip head bone screws into the superior and inferior vertebral body, a facet joint replacement device is selected based on the desired angular orientations of the superior articular surface and inferior articular surface. The desired angular orientations can be selected based on estimated angular orientations of the articular surfaces of a healthy facet joint in the treated motion segment. 
     In some embodiments, it may desirable for inferior articulating element  104  to reside in a particular position within the enclosing body  106  at the time of implantation into the body. For example, in some embodiments, it is desirable that the inferior articulating element is positioned within the enclosing body  106  so that the inferior articulating surface  126  is at its closest position with respect to the superior articulating surface  128 . The position of the inferior articulating element  104  within the enclosing body  106  can be decided based on the position of the spine during implantation of the facet joint replacement device so that the inferior articulating surface  126  and superior articulating surface  128  conform to the natural position of the articular surfaces of the superior and inferior articular process of the spinal motion segment to be treated.  FIG.  13    depicts a removable clip  300  according to one embodiment. The removable clip  300  includes a receiving member  302 , a receiving member  304 , and a connector  306  extending between the receiving member  302  and receiving member  304 . The connector  306  prevents relative movement between the receiving member  302  and receiving member  304 . The receiving member  302  can be configured to removably secure to the superior attachment member  120 . The receiving member  304  can be configured to removably secure to a superior section of the exterior of the enclosing body  106 .  FIG.  14    depicts the removable clip  300  secured to the facet joint replacement device  100 . When the receiving member  302  and receiving member  304  are secured to the facet joint replacement device, the removable clip  300  can constrain relative movement of the inferior articulating body  118  within the enclosing body  106 . In some embodiments, the removable clip  300  is metallic. 
     Methods for implanting the facet joint replacement device  100  can optionally include securing the removable clip  300  to the facet joint replacement device  100  prior to implantation of the facet joint replacement device  100 . After the facet joint replacement device  100  is secured to the spine, the removable clip  300  can be removed from the facet joint replacement device to allow for movement of the inferior articulating body  118  within the enclosing body  106 . 
       FIG.  15    depicts a removable clip  310  according to another embodiment. The removable clip  310  includes a receiving member  312 , a receiving member  314 , and a connector  316  extending between the receiving member  312  and receiving member  314 . The connector  316  prevents relative movement between the receiving member  312  and receiving member  314  and is shaped to correspond to the curvature of a side of the facet joint replacement device  100 . The receiving member  312  can be configured to removably secure to the superior attachment member  120 . The receiving member  314  can be configured to secure to a section of the exterior of the enclosing body  106  near the inferior end.  FIG.  16    depicts the removable clip  310  secured to the facet joint replacement device  100 . When the receiving member  312  is secured to the superior attachment member  120 , the connector  316  extends along a medial side of the enclosing body  106  to the receiving member  314  at the inferior end of the enclosing body  106 . The receiving member  314  can be positioned at the inferior end of the enclosing body  106  such that the removable clip  310  is secured to the facet joint replacement device  100 . When the removable clip  310  is secured to the facet joint replacement device  100 , the removable clip  310  can constrain relative movement of the inferior articulating body  118  within the enclosing body  106 . In some embodiments, the removable clip  310  is metallic. 
     Methods for implanting the facet joint replacement device  100  can optionally include securing the removable clip  310  to the facet joint replacement device  100  prior to implantation of the facet joint replacement device  100 . After the facet joint replacement device  100  is secured to the spine, the removable clip  310  can be removed from the facet joint replacement device to allow for movement of the inferior articulating body  118  within the enclosing body  106 . 
       FIG.  17    depicts a posterior perspective view of a facet joint replacement device  400  and a fastener  440  according to another embodiment. The facet joint replacement device  400  includes many of the same or similar components as the facet joint replacement device  100  described with respect to  FIGS.  1 - 7   . The facet joint replacement device  400  includes an enclosing element  402  having an enclosing body  406  and an inferior attachment member  412 . The facet joint replacement device  400  also includes an inferior articulating element  404  having an articulating body  418  and a superior attachment member  420 . The articulating body  418  can include an articulating surface  426 , similar to articulating surface  126 . A portion of the interior surface of the enclosing body  406  can be shaped to form a superior articulating surface (not shown), similar to articulating surface  128 . The enclosing body  406  can include an opening  442  configured to receive the fastener  440 . The opening  442  is positioned on a medial section of the enclosing body  406 . In some embodiments, the opening  442  is positioned on an inferior section of the enclosing body  406 . In some embodiments, the opening  442  is positioned on a superior section of the enclosing body  406 . In some embodiments, the opening  442  is positioned mid-position between a superior end of the enclosing body  406  and an inferior end of the enclosing body  406 . The articulating body  418  can include a channel  444  configure to align with the opening  442  when in a particular position or range of particular positions within the enclosing body  406  and receive the fastener  440  when aligned with the opening  442 . The enclosing body includes a channel  446  configured to align with the channel  444  of the articulating body  418  when the articulating body is aligned with the opening  442 . The channel  444  can be configured to receive the fastener  440  when the fastener  440  passes through the opening  442  and channel  444 . In some embodiments, the channels  444  and  446  extend along an axis that is the same as, similar to, or parallel to axis  103  as described with respect to  FIG.  1 B . When the fastener  440  is inserted into the opening  442 , channel  444 , and/or channel  446 , the fastener  440  moves in an inferior, anterior, and lateral direction. If the fastener  440  is removed from the channel opening  442 , channel  444 , and/or channel  446 , the fastener  440  moves in a superior, posterior, and medial direction. 
     The fastener  440  can include threads configured to be received by complementary threads within the channel  444  and channel  446 . In some embodiments, the fastener  440  is a threaded screw. In some embodiments, the fastener  440  is a lag screw. When received within the channel  444  and the channel  446 , the fastener  440  can secure the articulating body  418  in a particular position within the enclosing body  406 . For example, the fastener  440  can secure the articulating body  418  within the enclosing body  406  so that the inferior articulating surface  426  is at its most proximal position with respect to the superior articulating surface of the enclosing body. By securing the articulating body  418  in a particular position within the enclosing body  406 , the fastener  440  can perform a similar function to the removable clip  300 . 
     In some embodiments, methods of implanting the facet joint replacement device  400  include securing the articulating body  418  in a desired position within the enclosing body  406  prior to implantation in the body using the fastener  440 . The fastener  440  can be removed after the facet joint replacement device  400  is secured to the spine. In some embodiments, the fastener  440  can remain positioned within the facet joint replacement device  400  following implantation. 
     In some embodiments, the depth of the fastener  440  within the facet joint replacement device  400  can be altered by rotating the fastener  440 . In some embodiments, changing the depth of the fastener  440  within the facet joint replacement device can change the distance between the inferior articulating surface  426  and the superior articulating surface of the enclosing body  406 . In some embodiments, the depth of the fastener  440  can be changed after implantation to provide a different distance between the inferior articulating surface  426  and the superior articulating surface of the enclosing body  406 . In some embodiments, the fastener  440  can allow for at least some movement between the inferior articulating surface  426  and superior articulating surface of the enclosing body at least some depths of the fastener  440 . 
       FIG.  18    depicts an exploded view of a facet joint replacement device  500  in accordance with another embodiment. The facet joint replacement device  500  includes many of the same or similar components as the facet joint replacement device  100  described with respect to  FIGS.  1 A- 7   . The facet joint replacement device  500  includes an enclosing element  502  having an enclosing body  506 , an inferior attachment member  512 , and an opening  516 . The facet joint replacement device  500  also includes an inferior articulating element  504  having an articulating body  518  and a superior attachment member  520 . The articulating body  518  can include an inferior articulating surface  526 , similar to inferior articulating surface  126 . The inferior articulating surface  526  can be convex. A portion of the interior surface of the enclosing body  506  can be shaped to form a superior articulating surface (not shown), similar to articulating surface  128 . The superior articulating surface of the facet joint replacement device  500  can be concave. The facet joint replacement device  500  further includes a veneer  550  configured to be positioned between the inferior articulating surface  526  and the superior articulating surface of the facet joint replacement device  500 . In some embodiments, the veneer has a thickness of 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, between 1 mm and 3 mm, between 1 mm and 2 mm, or between 2 mm and 3 mm. The veneer  550  can include a low friction material, such as high molecular weight polyethylene. In some embodiments, the veneer is formed of vitamin E impregnated polyethylene, which may function as a free radical scavenger. The veneer  550  can reduce friction and wear between the inferior articulating surface  526  and the superior articulating surface of the facet joint replacement device  500 . In some embodiments, the veneer  550  includes a concave side configured to engage the inferior articulating surface  526 . The veneer  550  can also include a convex side configured to engage the superior articulating surface of the facet joint replacement device  500 . In some embodiments, the veneer  550  can be secured to the inferior articulating surface  526 . In some embodiments, the veneer  550  can be secured to the inferior articulating surface  526  by a fastener, such as a screw. In an alternative embodiment, the veneer  550  can be formed as part of a sleeve configured to fit over at least a portion of the articulating body  518  including the inferior articulating surface  526 . 
       FIG.  19    depicts a posterior view of a facet joint replacement device  600  according to another embodiment. The facet joint replacement device  600  includes many of the same or similar components as the facet joint replacement device  100  described with respect to  FIGS.  1 A- 7   . The facet joint replacement device  600  includes an enclosing element  602  having an enclosing body  606  and an inferior attachment member  612 . The facet joint replacement device  600  also includes an inferior articulating element  604  having an articulating body  618  and a superior attachment member  620 . The articulating body  618  can include an articulating surface (not shown), similar to articulating surface  126 . A portion of the interior surface of the enclosing body  606  can be shaped to form a superior articulating surface (not shown), similar to articulating surface  128 . The inferior attachment member  612  includes a hole  613  and a textured surface  615 . The superior attachment member  620  includes a hole  621  and a textured surface  623 . The holes  613  and  621  can each receive a fastener, such as a threaded bone screw, to secure the facet joint replacement device  600  to the spine. 
     The shape of the inferior attachment member  612  allows for alignment of the inferior attachment member  612  with a superior attachment member of a facet joint replacement device positioned to replace a facet joint at an inferior contiguous vertebral body. The shape of the superior attachment member  620  allows for alignment of the superior attachment member  620  with an inferior attachment member of a facet joint replacement device positioned to replace a facet joint of a superior contiguous vertebral body. 
       FIG.  20    depicts a posterior view of the motion segment  200  and a motion segment  201  with a facet joint replacement device  600 A and a facet joint replacement device  600 B implanted ipsilaterally. The facet joint replacement device  600 A is positioned to replace the facet joint  260  of the motion segment  200 . The facet joint replacement device  600 B is positioned to replace a facet joint of the motion segment  201 , which is inferior to motion segment  200  and includes vertebral body  210 , vertebral body  207 , and intervertebral disc  217 . The facet joint replacement devices  600 A and  600 B include the same components as the facet joint replacement device  600  described herein. The facet joint replacement device  600 A includes a superior attachment member  620 A and an inferior attachment member  612 A, each having a hole and a textured surface. The facet joint replacement device  600 B includes a superior attachment member  620 B and an inferior attachment member  612 B, each having a hole and a textured surface. The superior attachment member  620 A is secured to the superior vertebral body  205  by a fastener  674  passing through the hole of the superior attachment member  620 A. The inferior attachment member  612 A is positioned so that the hole of the inferior attachment member  612 A aligns with the hole of the superior attachment member  620 B. The textured surfaces of the attachment members  612 A and  620 B can contact one another to provide friction or otherwise constrain movement of the attachment members  612 A and  620 B relative to one another once aligned. A fastener  676  extends through both the hole in the attachment member  612 A and the hole in the attachment member  620 B to secure the attachment members  612 A and  620 B to the inferior vertebral body  210 . A fastener  678  extends through the hole of the inferior attachment member  612 B to secure the attachment member  612 B to vertebral body  207 . In some embodiments, each of the fasteners  674 ,  676 , and  678  can include a bone screw and/or a threaded locking nut. 
     Methods of implanting facet joint replacement devices  600 A and  600 B can include aligning the opening of the inferior attachment member  612 A with the opening of the superior attachment member  620 B and securing the inferior attachment member  612 A and the superior attachment member  620 B to the same vertebral body by extending a fastener through the opening of the inferior attachment member  612 A device and the opening of the superior attachment member  620 B. 
       FIG.  21    depicts a removable clip  320  according to another embodiment. The removable clip  320  includes a hook member  322 , a receiving member  324 , and a connector  326  extending between the hook member  322  and receiving member  324 . The connector  326  prevents relative movement between the receiving member  322  and receiving member  324  and is shaped to correspond to the curvature of the posterior of the facet joint replacement device  600 . The hook member  322  can be configured to removably secure to the superior attachment member  620 . The receiving member  324  can be configured to secure to a section of the exterior of the enclosing body  606  near the inferior end.  FIG.  22    depicts the removable clip  320  secured to the facet joint replacement device  600 . When the hook member  322  is secured to the superior attachment member  620 , the connector  326  extends along a posterior section of the enclosing body  606  to the receiving member  324  at the inferior end of the enclosing body  606 . The receiving member  324  can be positioned at the inferior end of the enclosing body  606  such that the removable clip  320  is secured to the facet joint replacement device  600 . When the removable clip  320  is secured to the facet joint replacement device  600 , the removable clip  320  can constrain relative movement of the inferior articulating body  618  within the enclosing body  606 . In some embodiments, the removable clip  320  is metallic. 
     Methods for implanting the facet joint replacement device  600  can optionally include securing the removable clip  320  to the facet joint replacement device  600  prior to implantation of the facet joint replacement device  600 . After the facet joint replacement device  600  is secured to the spine, the removable clip  320  can be removed from the facet joint replacement device to allow for movement of the inferior articulating body  618  within the enclosing body  606 . 
     Details regarding the facet joint replacement devices, methods, systems and other features and embodiments, as described above with respect to  FIGS.  1 - 22    and as further described in U.S. Pat. No. 9,839,451, the entirety of which is hereby incorporated by reference, may be utilized in combination with, may be replaced by, or may be used in place of any of the features or embodiments described hereinbelow or elsewhere in the specification. 
       FIGS.  23 A-J  depict a facet joint replacement device  700  according to one embodiment.  FIGS.  23 A-D  depict perspective views of the facet joint replacement device  700 .  FIGS.  23 A-D  also includes three-dimensional coordinate axes indicating the superior (“S”), inferior (“I”), anterior (“A”), posterior (“P”), medial (“M”), and lateral (“L”) directions. As described herein, the terms superior, inferior, anterior, posterior, medial, and lateral, when describing portions of the devices herein, refer to portions of the device as they are intended to be oriented with respect to the human spine. 
       FIG.  23 A  depicts a top posterior perspective view of the facet joint replacement device  700 .  FIG.  23 B  depicts a top anterior perspective view of the facet joint replacement device  700 .  FIG.  23 C  depicts a bottom posterior perspective view of the facet joint replacement device  700 .  FIG.  23 D  depicts a bottom anterior perspective view of the facet joint replacement device  700 . 
       FIG.  23 E  depicts a posterior view of the facet joint replacement device  700 .  FIG.  23 F  depicts an anterior view of the facet joint replacement device  700 .  FIG.  23 G  depicts a first sagittal view of a lateral side of the facet joint replacement device  700 .  FIG.  23 H  depicts a second sagittal view of a medial side of the facet joint replacement device  700 .  FIG.  23 I  depicts a top view of the facet joint replacement device  700 .  FIG.  23 J  depicts a bottom view of the facet joint replacement device  700 . 
     As shown in  FIG.  23 A-J , the facet joint replacement device  700  includes an enclosing element  702  and an articulating element  704 . The enclosing element  702  includes an enclosing body  706  and an attachment member  712 . At least a portion of the enclosing body  706  can be dimensioned, shaped, or otherwise configured to correspond to the shape of a pars interarticularis of a vertebra. The enclosing element can include a superior end  708  and an inferior end  710 . 
     The enclosing body  706  can be shaped, dimensioned, or otherwise configured to correspond to the shape and/or size of a facet joint capsule of a healthy facet joint. The enclosing body  706  can be configured to perform the functions of a facet joint capsule of a healthy facet joint. 
     The enclosing body  706  can include a main body  707  and a cap  709 . In some embodiments, the cap  709  can be configured to secure to the main body  707 . In some embodiments, the cap  709  can be can be configured to releasably secure to the main body  707 . In some embodiments, the cap  709  can be configured to permanently secure to the main body  707 . 
     As shown in  FIG.  23 A-J , the cap  709  is positioned at the inferior end  710  of the enclosing body  706 . In some embodiments, the cap  709  can be positioned at the superior end  708  of the enclosing body  706 . 
     As shown in  FIGS.  23 A-J , the attachment member  712  can extend from a lateral surface of the enclosing body  706 . In some embodiments, the attachment member  712  can extend from a lateral surface of the main body  707 . In some embodiments, the attachment member  712  can extend laterally from the enclosing body  706 . In some embodiments, the attachment member  712  extends laterally from the main body  707  of the enclosing body  706 . In some embodiments, the attachment member  712  can extend inferiorly from the enclosing body  706 . In some embodiments, the attachment member  712  can extend inferiorly from the main body  707 . In some embodiments, the attachment member  712  can extend posteriorly from the enclosing body  706 . In some embodiments, the attachment member can extend posteriorly from the main body  707 . 
     In some embodiments, the attachment member  712  can include a first section  711  and a second section  713 . In some embodiments, the first section  711  can extend from the enclosing body  706  in lateral, posterior, and/or inferior directions. In some embodiments, the first section  711  can extend from the main body  707  in lateral, posterior, and/or inferior directions. In some embodiments, the second section  713  can extend from the first section  711  in lateral, anterior, and/or inferior directions. In some embodiments, the first section  711  and the second section  713  can connect at or form a bend  715 . In some embodiments, the bend  715  can be positioned lateral to the enclosing body  706 . 
     The attachment member  712  can be shaped and/or dimensioned to facilitate securement of the facet joint replacement device  700  to the spine. As shown in  FIGS.  23 A-J , the attachment member  712  can be a rod. However, the attachment member  712  can be any shape suitable for fixation directly or indirectly to a vertebral body. In some embodiments, the attachment member  712  can have a diameter of 5.5 mm. In some embodiments, the attachment member  712  can have a diameter of 1 mm, 2 mm, 3 mm, 4 mm, 4.5 mm, 5 mm, 5.5 mm, 6 mm, 6.5 mm, 7 mm, 8 mm, 9 mm, 10 mm, between 2 mm to 8 mm, between 4 mm to 6 mm, between 5 mm to 7 mm, or between 5 mm to 6 mm. In some embodiments, the attachment member  712  can have a length of 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, between 2 mm to 8 mm, between 4 mm to 6 mm, between 5 mm to 10 mm, between 10 mm to 15 mm, between 15 mm to 20 mm, between 20 mm to 25 mm, between 25 mm to 30 mm, between 15 mm to 30 mm, or less than 15 mm. 
     As shown in  FIGS.  23 A-J , the enclosing body  706  can include an outer shell  750  and a liner  752 . In some embodiments, the liner  752  covers an interior surface the outer shell  750 . 
     In some embodiments, the outer shell  750  is formed of or formed partially of one or more metals or metal alloys. In some embodiments, the outer shell  750  is formed of cobalt-chrome. For example, the outer shell  750  can be formed of cobalt-chromium, titanium, titanium-based alloys, or any other suitable metals or metal alloys. In some embodiments, the outer shell  750  can be ceramic or partially ceramic. In some embodiments, the outer shell  750  can include super-hard ceramics. 
     In some embodiments, the liner  752  is formed of a low friction material, such as high molecular weight polyethylene. In some embodiments, the liner  752  is formed of ultra-high molecular weight polyethylene. In some embodiments, the liner  752  is formed of vitamin E impregnated ultra-high molecular weight polyethylene, which may function as a free radical scavenger. In some embodiments, the material of the liner  752  can facilitate movement of the articulating element  704  within the enclosing body  706 . In some embodiments, the material of the liner  752  can prevent or reduce wear from friction due to movement of the articulating element  704  within the enclosing body  706 . 
     As shown in  FIGS.  23 A-J , in some embodiments, the facet joint replacement device  700  can include a plug  780 . In some embodiments, the plug  780  can be removably received within an opening in an exterior surface of the enclosing body  706 . 
       FIG.  24 A  depicts a first cross-sectional view of the enclosing element  702  taken along line  24 A- 24 A as shown in  FIG.  23 J .  FIG.  24 B  depicts a second cross-sectional view of the enclosing element  702  taken along line  24 B- 24 B as shown in  FIG.  23 J . As shown in  FIGS.  24 A-B , the enclosing body  706  can include an inner cavity  714  defined by an interior surface  754  of the enclosing body  706 . In some embodiments, the interior surface  754  can be an interior surface of the liner  752  of the enclosing body  706 . 
     The inner cavity  714  can be further defined by an opening  716  of the enclosing body  706 . In some embodiments, the opening  716  is positioned at the superior end  708  of the enclosing body. 
     As shown in  FIGS.  24 A-B , in some embodiments, the outer shell  750  can include an outer shell main body  750   a  and an outer shell cap  750   b . In some embodiments, the liner  752  can include a liner main body  752   a  and a liner cap  752   b . The outer shell main body  750   a  and liner main body  752   a  can for the main body  707 . The outer shell cap  750   b  and liner cap  752   b  can form the cap  709 . 
     In some embodiments, the enclosing body  706  can include a projection  756  extending inwardly relative to a surrounding area  758  of the interior surface  754 . In some embodiments, the projection  756  can be formed by at least a portion of the main body  707  and at least a portion of the cap  709 . In some embodiments, the projection  756  can be generally convex in shape. In some embodiments, the projection  756  is generally parabolic in shape. In some embodiments, the projection  756  can extend from an inferior portion of the enclosing body to a superior portion of the enclosing body  706 . 
     As shown in  FIGS.  24 A-B , the enclosing body  706  can include a channel  744 . The channel  744  can extend through the outer shell  750  and the liner  752 . In some embodiments, the channel  744  can be configured to receive fastener or the plug  780 . 
     As shown in  FIG.  24 B , In some embodiments, a portion of the interior surface  754  of the enclosing body  706  can be shaped to form an articulating surface  728 . In some embodiments, the interior surface  754  can be an interior surface of the liner  752  and a portion of the interior surface  754  can be shaped to form the articulating surface  728 . In some embodiments, the articulating surface  728  can be concave or at least partially concave. In some embodiments, the articulating surface  728  can be shaped/and or dimensioned to correspond to the shape, size, and/or concavity of an articular surface of a healthy superior articular process. In some embodiments, the articulating surface  728  can be positioned on a surface of the enclosing body  706  generally opposite the projection  756 . 
       FIGS.  25 A-M  depict views of the main body  707  of the enclosing body  706 .  FIG.  25 A  depicts a top posterior perspective view of the main body  707 .  FIG.  25 B  depicts a top anterior perspective view of the main body  707 .  FIG.  25 C  depicts a bottom posterior perspective view of the main body  707 .  FIG.  25 D  depicts a bottom anterior perspective view of the main body  707 .  FIG.  25 E  depicts a posterior view of main body  707 .  FIG.  25 F  depicts an anterior view of the main body  707 .  FIG.  25 G  depicts a first sagittal view of a lateral side of the main body  707 .  FIG.  25 H  depicts a second sagittal view of a medial side of the main body  707 .  FIG.  25 I  depicts a top view of the main body  707 .  FIG.  25 J  depicts a bottom view of the main body  707 .  FIG.  25 K  depicts a cross-sectional view of the main body  707  taken along line  25 K- 25 K as shown in  FIG.  25 E .  FIG.  25 L  depicts a first perspective view of a cross-section of the main body  707 .  FIG.  25 M  depicts a second perspective view of a cross-section of the main body  707 . 
     As shown in  FIGS.  25 A-M , the channel  744  can extend between an opening  742  on an exterior surface of the enclosing body  706  and an opening  743  on the interior surface  754  of the enclosing body  706 . In some embodiments, the opening  742  is positioned on the exterior surface of the outer shell  750 . In some embodiments, the interior surface  754  is an interior surface of the liner  752  and the opening  743  is positioned on the interior surface  754 . The channel  744  can include a threaded section  747  configured to engage a threaded section of the plug  780  or a fastener. In some embodiments, at least a portion of the threaded section  747  is formed in the outer shell  750 . In some embodiments, at least a portion of the threaded section  747  is formed in the liner  752 . 
     As shown in  FIG.  25 A-M , the main body  707  can include one or more recesses  776 . The recesses  776  can be dimensioned, shaped, or otherwise configured to engage coupling features of the cap  709  to releasably or permanently secure the cap  709  to the main body  707 . The enclosing body  706  can further include one or more ramps  777 . The ramps  777  can be dimensioned, shaped, or otherwise figures to direct the coupling features of the cap  709  towards the recesses  709 . 
       FIG.  26 A  depicts a first perspective view of the cap  709 .  FIG.  26 B  depicts a second perspective view of the cap  709 . As shown in  FIGS.  26 A-B , the cap  709  can include one or more tabs  778 . The one or more tabs  778  can be dimensioned, sized, or otherwise configured to be received within the recesses  776  of the main body  707 . In some embodiments, the ramps  777  of the main body  707  can be dimensioned, shaped, or otherwise configured to guide the tabs  778  towards the recesses  776  during coupling of the cap  709  to the main body  707 . In some embodiments, the tabs  778  can be configured to couple to the recesses  776  via a snap fit. 
       FIGS.  27 A-K  depict views of the articulating element  704 .  FIG.  27 A  depicts a top posterior perspective view of the articulating element  704 .  FIG.  27 B  depicts a top anterior perspective view of the articulating element  704 .  FIG.  27 C  depicts a bottom posterior perspective view of the articulating element  704 .  FIG.  27 D  depicts a bottom anterior perspective view of the articulating element  704 . 
       FIG.  27 E  depicts a posterior view of the articulating element  704 .  FIG.  27 F  depicts an anterior view of the articulating element  704 .  FIG.  27 G  depicts a first sagittal view of a lateral side of the articulating element  704 .  FIG.  27 H  depicts a second sagittal view of a medial side of the articulating element  704 .  FIG.  27 I  depicts a top view of the articulating element  704 .  FIG.  27 J  depicts a bottom view of the articulating element  704 .  FIG.  27 K  depicts a cross-sectional view of the articulating element  704  taken along line  27 K- 27 K as shown in  FIG.  27 E . 
     As shown in  FIGS.  27 A-K , the articulating element  704  includes an articulating body  718  and an attachment member  720 . As described herein, the articulating body  718  can be at least partially positioned within and configured to move within the inner cavity  714  of the enclosing body  706 . The articulating body  718  has a superior end  722  and an inferior end  724 . 
     As shown in  FIGS.  27 A-K , the attachment member  720  can extend from the superior end  722  of the articulating body  718 . In some embodiments, the attachment member  720  can extend superiorly from the articulating body  718 . In some embodiments, the attachment member  720  can extend laterally from the articulating body  718 . In some embodiments, the attachment member  720  can extend posteriorly from the articulating body  718 . 
     In some embodiments, the attachment member  720  can include a first section  721  and a second section  723 . In some embodiments, the first section  721  can extend from the articulating body  718  in superior, lateral, and/or posterior directions. In some embodiments, the second section  723  can extend from the first section in lateral and/or anterior directions. In some embodiments, the first section  721  and the second section  723  can connect at or form a bend  725 . In some embodiments, the bend  725  can be positioned lateral to the articulating body. 
     The attachment member  720  can be shaped and/or dimensioned to facilitate securement of the facet joint replacement device  700  to the spine. As shown in  FIGS.  27 A-J , the attachment member  720  can be a rod. However, the attachment member  720  can be any shape suitable for fixation directly or indirectly to a vertebral body. In some embodiments, the attachment member  720  can have a diameter of 5.5 mm. In some embodiments, the attachment member  720  can have a diameter of 1 mm, 2 mm, 3 mm, 4 mm, 4.5 mm, 5 mm, 5.5 mm, 6 mm, 6.5 mm, 7 mm, 8 mm, 9 mm, 10 mm, between 2 mm to 8 mm, between 4 mm to 6 mm, between 5 mm to 7 mm, or between 5 mm to 6 mm. In some embodiments, the attachment member  720  can have a length of 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, between 2 mm to 8 mm, between 4 mm to 6 mm, between 5 mm to 10 mm, between 10 mm to 15 mm, between 15 mm to 20 mm, between 20 mm to 25 mm, between 25 mm to 30 mm, between 15 mm to 30 mm, or less than 15 mm. 
     As shown in  FIGS.  27 A-K , In some embodiments, a portion of an exterior surface  764  of the articulating body  718  can be shaped to form an articulating surface  726 . In some embodiments, the articulating surface  726  can be convex or at least partially convex. In some embodiments, the articulating surface  726  can be shaped/and or dimensioned to correspond to the shape, size, and/or concavity of an articular surface of a healthy inferior articular process. 
     In some embodiments, the articulating surface  726  of the articulating body and the articulating surface  728  of the enclosing body have complementary surface shapes. In some embodiments, the articulating surface  726  and the articulating surface  728  are elliptical or generally elliptical, circular or generally circular, oval or generally oval, rounded, polygonal, oblong, symmetric, asymmetric, or any other suitable shape. In some embodiments, the articulating surface  726  and articulating surface  728  can be shaped such that force is applied symmetrically to the articulating  728  when the articulating element  726  contacts or otherwise applies a force upon the articulating surface  728 . 
     As shown in  FIGS.  27 A-K , the articulating body  718  can include a slot, groove, or recess  760  extending inwardly relative to a surrounding area  762  of the exterior surface  764 . In some embodiments, the projection  756  and recess  760  can be generally concave in shape. In some embodiments, the recess  760  can be generally parabolic in shape. In some embodiments, the recess  760  can extend from an inferior portion of the articulating body to a superior portion of the articulating body  718 . In some embodiments, the articulating surface  726  can be positioned on a face of the articulating body  718  generally opposite the recess  760 . 
     As shown in  FIGS.  27 A-K , the articulating body  718  can include an opening  749  on the exterior surface  764  of the articulating body  718 . The opening  749  can be dimensioned, positioned, or otherwise configured to align with the opening  743  of the enclosing body  706  while the articulating body  718  is located at a particular position within the enclosing body  706 . As shown in  FIG.  27 J , a channel  746  extends from the opening  749  into the interior of the articulating body  718 . The channel  746  can be shaped, dimensioned, or otherwise configured to receive a fastener. In some embodiments, the channel  746  can include a threaded portion configured to couple with a threaded portion of a fastener. 
     In some embodiments, the articulating body  718  is formed of or formed partially of one or more metals or metal alloys. In some embodiments, the articulating body  718  is formed of cobalt-chrome. For example, the articulating body  718  can be formed of cobalt-chromium, titanium, titanium-based alloys, or any other suitable metals or metal alloys. In some embodiments, the articulating body  718  can be ceramic or partially ceramic. In some embodiments, the articulating body  718  can include super-hard ceramics. 
       FIG.  28    is an exploded view of a facet joint replacement system including the facet joint replacement device  700  and a fastener  740 . As described further herein, in some embodiments, the fastener  740  can be used to restrict movement of the articulating body  718  within the enclosing body  706 . 
     As shown in  FIG.  28   , in some embodiments, the attachment portion  720  can be releasably or permanently coupled to the articulating body  718 . In some embodiments, the attachment portion  720  can be coupled to the articulating body  718  via a tapered connection. In some embodiments, the attachment portion  720  can be coupled to the articulating body  718  via a threaded connection. 
     In some embodiments, the articulating body  718  can include an opening  766  configured to receive a portion  768  of the attachment portion  720 . In some embodiments, the portion  768  can be an end of the attachment portion  720 . In some embodiments, the portion  768  can be a tapered end of the attachment portion  720 . In some embodiments the portion  768  can be a keyed taper. In some embodiments, the portion  768  can be an externally threaded section and the opening  766  can include an internally threaded section configured to receive the externally threaded portion  768 . 
       FIGS.  29 A-D  depict views of the facet joint replacement device  700  in which the enclosing element  702  is illustrated as transparent to show internal features of the facet joint replacement device  700 .  FIG.  29 A  depicts a posterior view of the facet joint replacement device  700 .  FIGS.  29 B-D  depict posterior-medial views of the facet joint replacement device  700 .  FIGS.  29 E-G  depict posterior-medial cross-sectional views of the facet joint replacement device  700  taken along lines  24 B- 24 B as shown in  FIG.  23 J . 
     The articulating body  718  is configured to move within the enclosing body  706  in at least one direction. When the attachment member  720  is secured to a superior vertebral body and the attachment member  712  is secured to an inferior vertebral body, movement between the superior and inferior vertebral bodies can cause movement of the attachment member  720  with respect to the position of the enclosing body  706  resulting from the attachment member  712  being secured to the inferior vertebral body. Movement of the attachment member  720  with respect to the enclosing body  706  causes movement of the articulating body  718  within the enclosing body  706  generally along the interior surface  754  of the enclosing body  706 . 
       FIGS.  29 A-D  further show an axis  703 . The axis  703  represents an axis of articulation of the articulating body  718  within the enclosing body  706  and/or an axis of articulation of the articulating surfaces  726  and  728  relative to one another. The articulating body  718  can be configured to move along the axis  703  within the enclosing body. As shown in  FIGS.  29 A-D , the axis  703  can be parallel with a superior-inferior anatomical axis when the facet joint replacement device  700  is implanted within a patient. In some embodiments, the axis  703  can be parallel with an angle formed between the articulating surfaces  726  and  728 . 
       FIG.  30 A  depicts a posterior view of the facet joint replacement device  700  showing the axis  703 .  FIG.  30 B  depicts a sagittal view showing a lateral side of the facet joint replacement device  700  showing the axis  703 .  FIG.  30 C  shows a cross-sectional view of the facet joint replacement device  700  taken along line  30 C- 30 C as shown in  FIG.  23 J  and showing the axis  703 . 
     The attachment member  720  is configured to move along axis  703  towards and away from the enclosing body  706 . When the attachment member  720  moves towards the enclosing body  106  along the axis  703 , the attachment member  720  moves along the axis  703  in an inferior direction. When the attachment member  720  moves away from the enclosing body  706  along the axis  703 , the attachment member  720  moves along the axis  703  in a superior direction. The articulating body  718  moves along the axis  703  in the same manner when the attachment member  720  moves along the axis  703 . Although relative movement of the attachment member  720  towards and away from the enclosing body  706  is discussed, one of skill in the art would understand that movement between the enclosing body  706  and attachment member  720  could be described as movement of the enclosing body  706  towards or away from the attachment member  720  or movement of the enclosing body  706  and attachment member  720  towards or away from each other. 
     Movement of the attachment member  720  with respect to the enclosing body  706  causes movement of the articulating surface  726  relative to the articulating surface  728 . In some embodiments, movement of the attachment member  720  with respect to the enclosing body  706  causes movement of the articulating surface  726  along the axis  703  relative to the articulating surface  728 . In some embodiments, the articulating surface  726  can be configured to articulate relative to the articulating surface  728  by moving substantially only parallel to an angle formed by the two juxtaposed articulating surfaces  726  and  778 . Although relative movement of the articulating surface  726  relative to the articulating surface  728  is discussed, one of skill in the art would understand that movement between the articulating surface  726  and the articulating surface  728  could be described as movement of the articulating surface  728  relative to the articulating surface  728  or movement of the articulating surfaces  726  and  728  relative to each other. The axis  703  can represent the direction of relative movement between the articular surfaces of a healthy facet joint. In some embodiments, the articulating surfaces  726  and  728  can be configured to articulate relative each other by moving substantially only parallel to an angle formed by the two juxtaposed articulating surfaces  726  and  778 . 
     In some embodiments, the enclosing body  706  acts to limit relative movement between the articulating surface  726  and the articulating surface  728  along the axis  703 . In some embodiments, the enclosing body  706  acts to limit relative movement of the articling surface  726  and articulating surface  728  perpendicular to the axis  703 . In some embodiments, the enclosing body  706  can act to limit relative movement between the articulating surfaces  726  and  728  to correspond to the limitations of movement of the articular surfaces of a healthy facet joint. In some embodiments, the enclosing body  706  can act to limit movement between the articulating surfaces  726  and  728  to correspond to the limitations of movement provided by the facet joint capsule of a healthy facet joint. In any of the embodiments described above or elsewhere in this specification, the enclosing body can be configured to restrict movement of the articulating body within the enclosing body such that the articulating surface  726  moves only along an axis parallel with the superior/inferior axis of the patient. In some embodiments, the enclosing body  706  can be configured to restrict movement of the articulating body  718  within the enclosing body such that the articulating body  718  moves only along an axis parallel with an angle formed by the juxtaposed articulating surface  726  and articulating surface  728 . In some embodiments, the enclosing body  706  can be configured to restrict movement of the articulating body  718  within the enclosing body  706  such that the articulating surface  726  moves only along an axis parallel with an angle formed by the juxtaposed articulating surfaces  726  and  728 . 
     When the articulating body  718  moves within the enclosing body  706 , the articulating surface  726  can contact the articulating surface  728 . The articulating surface  726  can articulate against the articulating surface  728 . In some embodiments, the articulating surfaces  726  and  728  may apply an axial load to one another during articulation. In some embodiments, the outer shell  750  and/or liner  752  may have a sufficient thickness at articulating surface  728  to receive an axial load supplied by the articulating body  718  to the articulating surface  728  due to movement of the articulating body  718  within the enclosing body  706 . In some embodiments, the articulating body  718  may have a sufficient thickness at articulating surface  726  to receive an axial load supplied by the enclosing body  706  to the articulating surface  728  due to movement of the articulating body  718  within the enclosing body  706 . 
     Although articulation between the articulating surface  726  and the articulating surface  728  is discussed herein, it is contemplated that articulation between any or all of the exterior surfaces of the articulating body  718  and any or all of the interior surfaces of the enclosing body  706  could occur alternatively or in addition to articulating between the articulating surface  726  and the articulating surface  728 . 
     In some embodiments, the enclosing body  706  and articulating body  718  are configured such that a maximum distance between a center point of the articulating surface  726  and the articulating surface  728  is 0.5 mm, 1.0 mm, 1.5 mm, 1.75 mm, 2.0 mm, 2.25 mm, 2.5 mm, 3.0 mm, 3.5 mm, 4.0 mm, 5.0 mm, less than 2.0 mm, less than 3.0 mm, less than 4.0 mm, between 1.0 mm and 3.0 mm, between 1.0 mm and 2.0 mm, between 2.0 mm and 3.0 mm, between 1.5 mm and 2.5 mm, or between 1.75 mm and 2.25 mm. 
     As shown in  FIGS.  29 A-D , in some embodiments, a portion of the articulating body  718  can extend or align with the opening  716  of the enclosing body. In some embodiments, the opening  716  is dimensioned, shaped, or otherwise configured to prevent removal of the articulating body  718  through the opening  716 . For example, in some embodiments, at least some sections of the articulating body  718  are wider than the opening  716 . In some embodiments, the superior end  708  can be shaped, dimensioned, or otherwise configured to prevent removal of the articulating body  718  from the enclosing body  706 . For example, in some embodiments, a cross-section of the enclosing body  706  at or near the superior end  708  is narrower than a cross-section of at least a portion of the articulating body  718 . In some embodiments, the enclosing body  706  can taper such that a cross-section of the enclosing body  706  is narrower at the superior end  708  or near the superior end  708  than at a more inferior segment of the enclosing body  706 . 
     In some embodiments, the enclosing body  706  is shaped, dimensioned, or otherwise configured to circumferentially enclose the articulating surface  726  and the articulating surface  728 . In some embodiments, the enclosing body  706  encloses an entire circumferential portion of the articulating body  718  that includes the articulating surface  726 . In some embodiments, the liner  752  is shaped, dimensioned, or otherwise configured to circumferentially enclose the articulating surface  726  and the articulating surface  728 . In some embodiments, the liner  752  encloses an entire circumferential portion of the articulating body  718  that includes the articulating surface  726 . 
       FIGS.  29 A,  29 B, and  29 E  depict the articulating body  718  at a neutral position within the enclosing body  706 . The neutral position can refer to a position in which the opening  749  and/or channel  746  of the articulating body  718  is aligned with the opening  743  and/or channel  744  of the enclosing body  706 . In some embodiments, the neutral position is a mid-position between a superior-most articulating position and an inferior-most articulating position over which the articulating body  718  can move within the enclosing body  706 .  FIGS.  29 C and  29 F  show the articulating body  718  at a position superior to the neutral position within the enclosing body  706 .  FIGS.  29 D and  29 G  show the articulating body  718  at a position inferior to the neutral position within the enclosing body  706 . As shown in  FIG.  29 A-D , the articulating body  718  can move along the axis  703  within the enclosing body while the plug  780  is positioned within the channel  744  of the enclosing body. 
     When the articulating body  718  is positioned within the enclosing body  706 , the recess  760  receives the projection  756 . In other words, the projection  756  is positioned within the recess  760 . In some embodiments, the recess  760  and the projection  756  can have complementary shapes and/or dimensions. The recess  760  and/or projection  756  can be shaped, dimensioned, or otherwise configured to prevent relative rotation of the articulating body  718  within the enclosing body  706  when the projection  756  is received within the recess  760 . The recess  760  and/or projection  756  can be shaped, dimensioned, or otherwise configured to allow relative movement between the articulating surface  726  and the articulating surface  728  along the axis  703 . As shown in  FIGS.  29 A-C , the axis  703  can be generally aligned with a longitudinal axis of the recess  760 . The recess  760  can be configured to move superiorly and inferiorly relative to the projection  756 , and/or the projection  756  can be configured to move superiorly and inferiorly within the recess  760 . 
     Although a single projection  756  and a single recess  760  are shown, any number of projections and recesses may be utilized to prevent relative rotation of the articulating body  718  within the enclosing body  706 . 
     In some embodiments, the enclosing body  706  is configured to protect the surrounding anatomy from friction, damage, or infection due to the movement of components, including the articulating surface  726  and articulating surface  728  in the interior of the enclosing body  706 , for example, by acting as a physical barrier. For example, the enclosing body  706  can protect an adjacent thecal sac and adjacent nerve roots from involvement with the articulating surfaces  726  and  728  during relative movement between the articulating surfaces  726  and  728 . In some embodiments, the enclosing body  706  is configured to protect the components within the interior of the enclosing body  706  from damage, wear, or fibrosis due to the surrounding anatomy, for example, by acting as a physical barrier. 
     As shown in  FIG.  30 C , the articulating body  718  can include a tapered channel  770 . The tapered channel  770  can be configured to receive the portion  768  of the attachment portion  720  to releasably or permanently couple the attachment portion  720  to the articulating body  718 . 
       FIGS.  31 A-C  depict an example of stages of coupling the cap  709  to the main body  707  of the facet joint replacement device  700 .  FIG.  31 A  depicts a cross-sectional view of the facet joint replacement device  700  showing the cap  709  separated from the main body  707 .  FIG.  31 B  depicts a cross-sectional view showing the cap  709  partially engaging the main body  707 . In  FIG.  31 B , the tabs  778  of the cap  709  are positioned in engagement with the ramps  777  of the main body  707 . When the tabs  778  are engaged with the ramps  777 , the cap  709  can be moved towards the main body  707  to cause the tabs  778  to engage the recesses  776 .  FIG.  31 C  depicts a cross-sectional view of the facet joint replacement device  700  showing the cap  709  coupled to the main body  707 . As shown in  FIG.  31 C , the tabs  778  are engaged with the recesses  776 . 
       FIG.  31 D  depicts an exploded perspective view of the facet joint replacement device  700  showing the cap  709  separated from the main body  707 .  FIG.  31 E  depicts a perspective view of the facet joint replacement device  700  showing the cap  709  coupled to the main body  707 .  FIG.  31 F  depicts a cross-sectional perspective view of the facet joint replacement device  700  showing the cap  709  separated from the main body  707 .  FIG.  31 G  depicts a cross-sectional perspective view of the facet joint replacement device  700  showing the cap  709  coupled to the main body  707 . 
       FIGS.  32 A-C  depict a top perspective, bottom perspective, and front view of the fastener  740 . As shown in  FIGS.  32 A-C , the fastener  740  can include an externally threaded portion  737 , a generally cylindrical portion  739 , and a tip  741 . 
     In some embodiments, the fastener  740  is formed of or formed partially of one or more metals or metal alloys. For example, the fastener  740  can be formed of cobalt-chromium, titanium, titanium-based alloys, or any other suitable metals or metal alloys. In some embodiments, the fastener  740  can be ceramic or partially ceramic. In some embodiments, the fastener  740  can include super-hard ceramics. 
       FIGS.  32 D and  32 E  illustrate a cross-sectional view and a perspective cross-sectional view, respectively, showing the fastener  740  positioned within the channels  744  and  746  of the enclosing body  706  and articulating element  718 . As shown in  FIGS.  32 D and  32 E , the externally threaded section  737  of the fastener  740  can removably secure to the internally threaded section  747  of the channel  744 . In some embodiments, the externally threaded section  737  of the fastener  740  can removably secure to an internally threaded section of the channel  746 . When positioned within the channels  744  and  746 , the fastener  704  can prevent movement of the articulating body  718  relative to the enclosing body  706 . When positioned within the channels  744  and  746 , the fastener  744  can maintain the articulating body  718  at the neutral position within the channels  744  and  746 . 
       FIGS.  33 A and  33 B  illustrate a top perspective view and a bottom perspective view, respectively of the plug  780 . As shown in  FIGS.  33 A and  32 B , the plug  780  can include an externally threaded section  781 . 
     In some embodiments, the plug  780  is formed of or formed partially of one or more metals or metal alloys. For example, the plug  780  can be formed of cobalt-chromium, titanium, titanium-based alloys, or any other suitable metals or metal alloys. In some embodiments, the plug  780  can be ceramic or partially ceramic. In some embodiments, the plug  780  can include super-hard ceramics. 
       FIGS.  33 C and  33 D  illustrate a cross-sectional view and a perspective cross-sectional view, respectively, showing the plug  780  positioned within the channel  744 . As shown in  FIGS.  33 C and  33 D , the externally threaded section  781  of the plug  780  can removably secure to the internally threaded section  747  of the channel  744 . In some embodiments, the plug is shaped, dimensioned, or otherwise configured to extend through only a portion of the channel  744 . The plug  780  can be dimensioned, shaped, or otherwise configured such that when the plug  780  is positioned within the facet joint replacement device  700 , the plug  780  does not extend into the channel  746 . When the plug  780  is positioned within the facet joint replacement device  700 , the plug  780  does not restrict movement of the articulating body  718  within the enclosing body  706 . In some embodiments, the plug  780  is shaped, dimensioned, or otherwise configured to fit flush with an exterior surface of the enclosing body  706 . 
     When positioned within the enclosing body  706 , the plug  780  can seal the opening  742  and/or channel  744  relative to the surrounding anatomy. By sealing the opening  742  and/or channel  744 , the plug  780  can act as a physical barrier along with enclosing body  706  to protect the surrounding anatomy from friction, damage, or infection due to the movement of components, including the articulating surface  726  and articulating surface  728  in the interior of the enclosing body  706 . For example, the enclosing body  706  and plug  780  can protect an adjacent thecal sac and adjacent nerve roots from involvement with the articulating surfaces  726  and  728  during relative movement between the articulating surfaces  726  and  728 . In some embodiments, the plug  780  and enclosing body  706  are configured to protect the components within the interior of the enclosing body  706  from damage, wear, or fibrosis due to the surrounding anatomy, for example, by acting as a physical barrier. 
       FIGS.  34 A-D  depict a posterior view, a sagittal view, a bottom view, and a perspective view, respectively of a lumbar motion segment  200  with the facet joint replacement device  700  implanted.  FIGS.  34 A-D  also depict a sagittal plane  802 , a transverse plane  804 , and a frontal plan  806 . 
     The attachment member  720  is affixed to the pedicle  240  of the superior vertebra or superior vertebral body  205  by a fastener  874 . The attachment member  712  is affixed to the pedicle  242  of the interior vertebra or inferior vertebral body  210  by a fastener  876 . In alternative embodiments, an attachment member of an enclosing element  702 , such as attachment member  712 , can be secured to the superior vertebral body  205  and an attachment member of an articulating element  704 , such as attachment member  720  can be secured to the inferior vertebral body  210 . While the attachment member  720  of the articulating body  718  is shown extending superiorly from the opening  716  of the enclosing body  706  herein, in some embodiments the attachment member  720  can extend inferiorly from an opening at the inferior end  710  of the enclosing body  706 . 
     As shown in  FIGS.  34 A-D , the fasteners  874  and  876  each include a tulip head bone screw and a top loading set screw.  FIGS.  34 E-G  show the positioning of the tulip head bone screws of fasteners  874  and  876  within pedicles  240  and  242 . 
     When the facet joint replacement device  700  is implanted, the articulating surface  726  can be shaped, dimensioned, or otherwise configured to face at least partially in an anterior and lateral direction. When the facet joint replacement device  700  is implanted, the articulating surface  726  can be shaped, dimensioned, or otherwise configured to face in a direction that corresponds to that of an inferior articular surface of a healthy facet joint. When the facet joint replacement device  700  is implanted, the articulating surface  728  can be shaped, dimensioned, or otherwise configured to face at least partially in a posterior and medial direction. When the facet joint replacement device  700  is implanted, the articulating surface  728  can be shaped, dimensioned, or otherwise configured to face in a direction that corresponds to that of a superior articular surface of a healthy facet joint. In some embodiments, when the facet joint replacement device  700  is implanted, the enclosing body  706  can be located at an anatomical location corresponding to that of a healthy facet joint. In some embodiments, when the attachment member  712  is fixed relative to the inferior vertebral body and the attachment member  720  is fixed relative to the superior vertebral body, the attachment member  712  and/or the attachment member  720  can be shaped, dimensioned, or otherwise configured to locate the articulating surfaces  726  and  728  at a location corresponding to the location of the articular surfaces within the a healthy facet joint. 
       FIGS.  34 A-G  show a unilateral implantation of a facet joint replacement device  700 . One of skill in the art would understand that a facet joint replacement device, such as facet joint replacement device  700 , can be implanted on either lateral side of a motion segment, or two facet joint replacement devices can be implanted bilaterally, one on each side of a particular motion segment, for example, as described with respect to  FIG.  12   . One of skill in the art would further understand that two facet joint replacement devices, such as facet joint replacement device  700 , can be implanted ipsilaterally, as described with respect to  FIG.  20   . 
     As described herein, the components of the facet joint replacement device  700  can be shaped and/or dimensioned to correspond to the anatomy of a healthy facet joint and related spinal motion segment. While lumbar facet joints are shown and described herein, applications of the facet joint replacement device  700  are not limited to the lumbar spine. In some embodiments, the facet joint replacement device  700  can be shaped and/or dimensioned to correspond to the anatomy of the thoracic spine. In some embodiments, a vertical distance between the superior end  708  of the enclosing body and the inferior end  710  of the enclosing body is between 20 mm to 44 mm, between 24 mm to 40 mm, between 28 mm and 36 mm, or between 30 mm and 34 mm. In some embodiments a vertical distance between the superior end  708  of the enclosing body and the inferior end  710  of the enclosing body is 28 mm, 29 mm, 30 mm, 31 mm, 32 mm, 33 mm, 34 mm, 35 mm, or 36 mm. In some embodiments, the facet joint replacement device  700  can be shaped and/or dimensioned to correspond to the anatomy of the cervical spine. 
     In some embodiments, one or both of the articulating surface  728  and articulating surface  726  can have a major axis length of 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, 16 mm, 17 mm, 18 mm, between 10 mm to 25 mm, between 9 to 14 mm, between 10 to 14 mm, or between 12 mm to 14 mm. In some embodiments, one or both of the articulating surface  128  and articulating surface  126  can have a minor axis length of 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, 16 mm, 17 mm, 18 mm, between 8 mm to 25 mm, between 8 mm to 14 mm, between 9 mm to 14 mm, or between 12 mm to 14 mm. 
       FIG.  35    depicts a bottom view of the facet joint replacement device  700  showing an axis  790  parallel to a sagittal anatomic plane extending through a center point of the articulating surface  726 , and axis  792  parallel to a frontal anatomic plane and extending through a center point of the articulating surface  726 , and an axis  794  extending through the center point of the articulating surface  726  and perpendicular to a tangent of the articulating surface  726  at the center point. As shown in  FIG.  35   , an angle α extends between the axis  790  and the axis  794 . An angle β extends between the axis  792  and  794 . In some embodiments, the angle α can be between 30° and 60°, between 35° and 55°, between 40° and 50°, or any other suitable range. In some embodiments, the angle α can be 30°, 35°, 40°, 45°, 50°, 55°, 60°, or any other suitable angle. In some embodiments, the angle β can be between 30° and 60°, between 35° and 55°, between 40° and 50°, or any other suitable range. In some embodiments, the angle β can be 30°, 35°, 40°, 45°, 50°, 55°, 60°, or any other suitable angle. In some embodiments, an angle between an axis extending through the center point of the articulating surface  726  parallel to a transverse anatomic plane and the axis  794  can be between 75° and 105°, between 80° to 100°, between 85° to 95° or any other suitable angle. In some embodiments, an angle between an axis extending through the center point of the articulating surface  726  parallel to a transverse anatomic plane and the axis  794  can be 75°, 80°, 85°, 90°, 95°, 100°, 105° or any other suitable angle. 
     Similarly, in some embodiments, an angle between an axis parallel to a frontal anatomic plane and extending through a center point of the articulating surface  728  and an axis extending through the center point of the articulating surface  728  and perpendicular to a tangent of the articulating surface  728  at the center point can be between 30° and 60°, between 35° and 55°, between 40° and 50°, or any other suitable range. In some embodiments, an angle between an axis parallel to a frontal anatomic plane and extending through a center point of the articulating surface  728  and an axis extending through the center point of the articulating surface  728  and perpendicular to a tangent of the articulating surface  728  at the center point can be 30°, 35°, 40°, 45°, 50°, 55°, 60°, or any other suitable angle. In some embodiments, an angle between an axis parallel to a sagittal anatomic plane and extending through a center point of the articulating surface  728  and an axis extending through the center point of the articulating surface  728  and perpendicular to a tangent of the articulating surface  728  at the center point can be between 30° and 60°, between 35° and 55°, between 40° and 50°, or any other suitable range. In some embodiments, an angle between an axis parallel to a sagittal anatomic plane and extending through a center point of the articulating surface  728  and an axis extending through the center point of the articulating surface  728  and perpendicular to a tangent of the articulating surface  728  at the center point can be 30°, 35°, 40°, 45°, 50°, 55°, 60°, or any other suitable angle. In some embodiments, an angle between an axis parallel to a transverse anatomic plane and extending through a center point of the articulating surface  728  and an axis extending through the center point of the articulating surface  728  and perpendicular to a tangent of the articulating surface  728  at the center point can be between 75° and 105°, between 80° to 100°, between 85° to 95° or any other suitable angle. In some embodiments, an angle between an axis parallel to a transverse anatomic plane and extending through a center point of the articulating surface  728  and an axis extending through the center point of the articulating surface  728  and perpendicular to a tangent of the articulating surface  728  at the center point can be 75°, 80°, 85°, 90°, 95°, 100°, 105°, or any other suitable angle. 
     In some embodiments, the axis  703  can be perpendicular to a transverse anatomic plane. In some embodiments, the axis  703  can be parallel to a sagittal anatomic plane. In some embodiments, the axis  703  can be parallel to a frontal anatomic plane. 
     As described herein, in some embodiments, the implant  700  can be shaped and/or dimensioned to correspond to the anatomy of the lumbar spine, thoracic spine, or cervical spine. 
     In some embodiments, an angle between the transverse anatomic plane and a mean orientation of the articulating surface  726  can be between 0° and 98°, between 10° and 88°, between 20° and 78°, or any other suitable angle for a facet joint replacement device  700  implanted within the cervical spine. In some embodiments, an angle between the transverse anatomic plane and a mean orientation of the articulating surface  726  can be between 35° and 100°, between 45° and 90°, between 55° and 80°, or any other suitable angle for a facet joint replacement device  700  implanted within the thoracic spine. In some embodiments, an angle between the transverse anatomic plane and a mean orientation of the articulating surface  726  can be between 62° and 106°, between 72° and 96°, between 82° and 86°, or any other suitable angle for a facet joint replacement device  700  implanted within the lumbar spine. In some embodiments, the transverse anatomic plane may be referred to as the 0° transverse plane. In some embodiments, the foregoing angles between the transverse anatomic plane and a mean orientation of the articulating surface  726  may be referred to as inclination angles of the articulating surface  726  within the sagittal anatomic plane. 
     In some embodiments, an angle between the sagittal anatomic plane and a mean orientation of the articulating surface  726  can be between 50° and 116°, between 60° and 106°, between 70° and 96°, or any other suitable angle for a facet joint replacement device  700  implanted within the cervical spine. In some embodiments, an angle between the sagittal anatomic plane and a mean orientation of the articulating surface  726  can be between 65° and 140°, between 75° and 130°, between 85° and 120°, or any other suitable angle for a facet joint replacement device  700  implanted within the thoracic spine. In some embodiments, an angle between the sagittal anatomic plane and a mean orientation of the articulating surface  726  can be between 0° and °  90 , between 5° and 80°, between 15° and 70°, or any other suitable angle for a facet joint replacement device  700  implanted within the lumbar spine. In some embodiments, the sagittal anatomic plane may be referred to as the 0° sagittal plane. In some embodiments, the foregoing angles between the sagittal anatomic plane and a mean orientation of the articulating surface  726  may be referred to as inclination angles of the articulating surface  726  within the transverse anatomic plane. 
     In some embodiments, the articulating surface  726  can be configured to articulate relative to the articulating surface  728  by moving substantially only parallel to an axis defined by the inclination angles of the articulating surface  726  within the sagittal and transverse anatomic planes. 
     In some embodiments, an angle between the transverse anatomic plane and a mean orientation of the articulating surface  728  can be between 0° and 98°, between 10° and 88°, between 20° and 78°, or any other suitable angle for a facet joint replacement device  700  implanted within the cervical spine. In some embodiments, an angle between the transverse anatomic plane and a mean orientation of the articulating surface  728  can be between 35° and 100°, between 45° and 90°, between 55° and 80°, or any other suitable angle for a facet joint replacement device  700  implanted within the thoracic spine. In some embodiments, an angle between the transverse anatomic plane and a mean orientation of the articulating surface  728  can be between 62° and 106°, between 72° and 96°, between 82° and 86°, or any other suitable angle for a facet joint replacement device  700  implanted within the lumbar spine. In some embodiments, the transverse anatomic plane may be referred to as the 0° transverse plane. In some embodiments, the foregoing angles between the transverse anatomic plane and a mean orientation of the articulating surface  728  may be referred to as inclination angles of the articulating surface  728  within the sagittal anatomic plane. 
     In some embodiments, an angle between the sagittal anatomic plane and a mean orientation of the articulating surface  728  can be between 50° and 116°, between 60° and 106°, between 70° and 96°, or any other suitable angle for a facet joint replacement device  700  implanted within the cervical spine. In some embodiments, an angle between the sagittal anatomic plane and a mean orientation of the articulating surface  728  can be between 65° and 140°, between 75° and 130°, between 85° and 120°, or any other suitable angle for a facet joint replacement device  700  implanted within the thoracic spine. In some embodiments, an angle between the sagittal anatomic plane and a mean orientation of the articulating surface  728  can be between 0° and °  90 , between 5° and 80°, between 15° and 70°, or any other suitable angle for a facet joint replacement device  700  implanted within the lumbar spine. In some embodiments, the sagittal anatomic plane may be referred to as the 0° sagittal plane. In some embodiments, the foregoing angles between the sagittal anatomic plane and a mean orientation of the articulating surface  728  may be referred to as inclination angles of the articulating surface  728  within the transverse anatomic plane. 
     In some embodiments, the articulating surface  728  can be configured to articulate relative to the articulating surface  726  by moving substantially only parallel to an axis defined by the inclination angles of the articulating surface  728  within the sagittal and transverse anatomic planes. 
       FIGS.  36 A-J  depict a facet joint replacement device  900  according to one embodiment. With the exception of the differences described herein, the facet joint replacement device  900  and the components thereof can have any of the same or similar features or functions as the facet joint replacement device  700 . 
       FIGS.  36 A-D  depict perspective views of the facet joint replacement device  900 .  FIGS.  36 A-D  also includes three-dimensional coordinate axes indicating the superior (“S”), inferior (“I”), anterior (“A”), posterior (“P”), medial (“M”), and lateral (“L”) directions. As described herein, the terms superior, inferior, anterior, posterior, medial, and lateral, when describing portions of the devices herein, refer to portions of the device as they are intended to be oriented with respect to the human spine. 
       FIG.  36 A  depicts a top posterior perspective view of the facet joint replacement device  900 .  FIG.  36 B  depicts a top anterior perspective view of the facet joint replacement device  900 .  FIG.  36 C  depicts a bottom posterior perspective view of the facet joint replacement device  900 .  FIG.  36 D  depicts a bottom anterior perspective view of the facet joint replacement device  900 . 
       FIG.  36 E  depicts a posterior view of the facet joint replacement device  900 .  FIG.  36 F  depicts an anterior view of the facet joint replacement device  900 .  FIG.  36 G  depicts a first sagittal view of a lateral side of the facet joint replacement device  900 .  FIG.  36 H  depicts a second sagittal view of a medial side of the facet joint replacement device  900 .  FIG.  36 I  depicts a top view of the facet joint replacement device  900 .  FIG.  36 J  depicts a bottom view of the facet joint replacement device  900 . 
     As shown in  FIG.  36 A-J , the facet joint replacement device  900  includes an enclosing element  902  and an articulating element  904 . The enclosing element  902  includes an enclosing body  906  and an attachment member  912 . At least a portion of the enclosing body  906  can be dimensioned, shaped, or otherwise configured to correspond to the shape of a pars interarticularis of a vertebra. The enclosing element can include a superior end  908  and an inferior end  910 . 
     The enclosing body  906  can be shaped, dimensioned, or otherwise configured to correspond to the shape and/or size of a facet joint capsule of a healthy facet joint. The enclosing body  906  can be configured to perform the functions of a facet joint capsule of a healthy facet joint. 
     The enclosing body  906  differs from the enclosing body  706  in that the enclosing body  906  does not include a separate main body and cap. Instead, portions of the enclosing body  906  similar to the main body  707  and cap  709  of the enclosing body  706  can be integrally or monolithically formed. 
     As shown in  FIGS.  36 A-J , the attachment member  912  can extend from a lateral surface of the enclosing body  906 . In some embodiments, the attachment member  912  can extend laterally from the enclosing body  906 . In some embodiments, the attachment member  912  can extend inferiorly from the enclosing body  906 . In some embodiments, the attachment member  912  can extend posteriorly from the enclosing body  906 . 
     In some embodiments, the attachment member  912  can include a first section  911  and a second section  913 . In some embodiments, the first section  911  can extend from the enclosing body  906  in lateral, posterior, and/or inferior directions. In some embodiments, the second section  913  can extend from the first section  911  in lateral, anterior, and/or inferior directions. In some embodiments, the first section  911  and the second section  913  can connect at or form a bend  915 . In some embodiments, the bend  915  can be positioned lateral to the enclosing body  906 . 
     The attachment member  912  can be shaped and/or dimensioned to facilitate securement of the facet joint replacement device  900  to the spine. As shown in  FIGS.  36 A-J , the attachment member  912  can be a rod. However, the attachment member  912  can be any shape suitable for fixation directly or indirectly to a vertebral body. In some embodiments, the attachment member  912  can have a diameter of 5.5 mm. In some embodiments, the attachment member  912  can have a diameter of 1 mm, 2 mm, 3 mm, 4 mm, 4.5 mm, 5 mm, 5.5 mm, 6 mm, 6.5 mm, 7 mm, 8 mm, 9 mm, 10 mm, between 2 mm to 8 mm, between 4 mm to 6 mm, between 5 mm to 7 mm, or between 5 mm to 6 mm. In some embodiments, the attachment member  912  can have a length of 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, between 2 mm to 8 mm, between 4 mm to 6 mm, between 5 mm to 10 mm, between 10 mm to 15 mm, between 15 mm to 20 mm, between 20 mm to 25 mm, between 25 mm to 30 mm, between 15 mm to 30 mm, or less than 15 mm. 
     As shown in  FIGS.  36 A-J , the enclosing body  906  can include an outer shell  950  and a liner  952 . In some embodiments, the liner  952  covers an interior surface the outer shell  950 . In some embodiments, a portion  953  of the liner  952  extends superiorly beyond a superior end of the outer shell  950 . 
     In some embodiments, the outer shell  950  is formed of or formed partially of one or more metals or metal alloys. In some embodiments, the outer shell  950  is formed of cobalt-chrome. For example, the outer shell  950  can be formed of cobalt-chromium, titanium, titanium-based alloys, or any other suitable metals or metal alloys. In some embodiments, the outer shell  950  can be ceramic or partially ceramic. In some embodiments, the outer shell  950  can include super-hard ceramics. 
     In some embodiments, the liner  952  is formed of a low friction material, such as high molecular weight polyethylene. In some embodiments, the liner  952  is formed of ultra-high molecular weight polyethylene. In some embodiments, the liner  952  is formed of vitamin E impregnated ultra-high molecular weight polyethylene, which may function as a free radical scavenger. In some embodiments, the material of the liner  952  can facilitate movement of the articulating element  904  within the enclosing body  906 . In some embodiments, the material of the liner  952  can prevent or reduce wear from friction due to movement of the articulating element  904  within the enclosing body  906 . 
     In some embodiments, the liner  952  and/or the outer shell  950  can include one or surface features to provide a connection between the liner  952  and outer shell  950  and/or to prevent or restrict relative motion between the liner  952  and the outer shell  950 . For example, one of the liner  952  and the outer shell  950  can include a plurality of protrusions and the other of the liner  952  and shell  950  can include a plurality of corresponding recesses or openings configured to receive the protrusions. In some embodiments, the liner  952  can be molded into the outer shell  950 . In some embodiments, the outer shell  950  and/or liner  952  can include one or more surface features configured to facilitate coupling between the outer shell  950  and the liner  952  during the molding process. For example,  FIG.  46    depicts an embodiment of the outer shell  950  having a scaffold  951  extending from an inner surface of the outer shell  950 . In some embodiments, the scaffold  951  can be integrally formed with the inner surface of the outer shell  950 . In some embodiments, during the molding process, the scaffolding  951  can form a connection with the liner  952 . For example, in some embodiments, the scaffolding  951  may be embedded within the scaffolding  952  during the molding process. In some embodiments, the scaffolding  951  can form a porous and/or textured surface to which the liner  952  can interdigitate for form connection. In some embodiments, the scaffolding  951  can form a porous and/or textured surface to which the liner  952  can interdigitate for form a durable and permanent connection. 
     As shown in  FIGS.  36 A-J , in some embodiments, the facet joint replacement device  900  can include a plug  980 . In some embodiments, the plug  980  can be removably received within an opening in an exterior surface of the enclosing body  906 . 
     As shown in  FIGS.  36 A-J , the enclosing element  902  can include a retention plate  917 . The retention plate  917  can be configured to couple to the liner  952  and/or the shell  950  to form the enclosing body  906 . In some embodiments, the retention plate  917  is positioned at the superior end  908  of the enclosing body. In some embodiments, the retention plate can couple to the portion  953  of the liner  952 . In some embodiments, the retention plate  917  can be releasably or permanently secured to the liner  952  and/or the shell  950 . For example, in some embodiments, the liner  952  can be molded around at least a portion of the retention plate  917 . 
     In some embodiments, the retention plate  917  can at least partially form a barrier to restrict movement of the articulating element  904  in a superior direction relative to the enclosing body  906 . 
       FIG.  37 A  depicts a posterior longitudinal cross-sectional view of the enclosing element  902  taken along line  37 A- 37 A as shown in  FIG.  36 J .  FIG.  37 B  depicts an anterior longitudinal cross-sectional view of the enclosing element  902  taken along line  37 B- 37 B as shown in  FIG.  36 J .  FIG.  37 C  depicts a top view of the enclosing element  902 .  FIG.  37 D  depicts a bottom cross-sectional view of the enclosing element  902 .  FIG.  37 E  depicts a first perspective view of a cross-section of the enclosing element  902 .  FIG.  37 F  depicts a second perspective view of a cross-section of the enclosing element  902 .  FIG.  37 G  depicts a fourth cross-sectional view of the enclosing element  902 .  FIG.  37 H  depicts a third perspective view of a cross-section of the enclosing element  902 .  FIG.  37 I  depicts a fourth perspective view of a cross-section of the enclosing element  902 . 
     As shown in  FIGS.  37 A-I , the enclosing body  906  can include an inner cavity  914  defined by an interior surface  954  of the enclosing body  906 . In some embodiments, the interior surface  954  can be an interior surface of the liner  952  of the enclosing body  906 . 
     The inner cavity  914  can be further defined by an opening  1006  of the enclosing body  906 . In some embodiments, the opening  1006  is positioned at the superior end  908  of the enclosing body. As shown in  FIG.  37 A , the opening  1006  is defined by the retainer or retention plate  917 . In some embodiments, the opening  1006  can at least partially align with an opening  916  of the outer shell  950  and liner  952 . In some embodiments, the inner cavity  914  can be defined by a bottom surface of the retention plate  917 . 
     In some embodiments, the retention plate  917  is formed of a low friction material, such as high molecular weight polyethylene. In some embodiments, the retention plate  917  is formed of ultra-high molecular weight polyethylene. In some embodiments, the retention plate  917  is formed of vitamin E impregnated ultra-high molecular weight polyethylene, which may function as a free radical scavenger. 
     As shown in  FIG.  37 A-B , the retention plate  917  can include a base layer  1004  having a lip  1008  configured to be secured within a cavity  973  of the liner  952 . In some embodiments, the cavity  973  can be formed by at least partially formed by a lip  971  of the liner  952 . In some embodiments, the retention plate can include a top layer  1002  positioned superior to the base layer  1004  and having a smaller cross-sectional area than the base layer  1004 . 
     In some embodiments, the base layer  1004  can at least partially form a barrier to restrict movement of the articulating element  904  within the enclosing body  906 . For example, in some embodiments, the base layer  1004  can at least partially form a barrier to restrict movement in a superior direction relative to the enclosing body  906 . 
     In some embodiments, the top layer of the retention plate can couple with the liner  1052  to form a barrier between the inner cavity  914  and the external environment. 
     In some embodiments, the enclosing body  906  can include a projection  956  extending inwardly relative to a surrounding area  958  of the interior surface  954 . In some embodiments, the projection  956  can be generally convex in shape. In some embodiments, the projection  956  is generally parabolic in shape. In some embodiments, the projection  956  can extend from an inferior portion of the enclosing body to a superior portion of the enclosing body  906 . 
     As shown in  FIGS.  37 A-H , the enclosing body  906  can include a channel  944 . The channel  944  can extend through the outer shell  950  and the liner  952 . In some embodiments, the channel  944  can be configured to receive fastener or the plug  980 . 
     As shown in  FIG.  37 B , In some embodiments, a portion of the interior surface  954  of the enclosing body  906  can be shaped to form an articulating surface  928 . In some embodiments, the interior surface  954  can be an interior surface of the liner  952  and a portion of the interior surface  954  can be shaped to form the articulating surface  928 . In some embodiments, the articulating surface  928  can be concave or at least partially concave. In some embodiments, the articulating surface  928  can be shaped/and or dimensioned to correspond to the shape, size, and/or concavity of an articular surface of a healthy superior articular process. In some embodiments, the articulating surface  928  can be positioned on a surface of the enclosing body  906  generally opposite the projection  956 . 
     As shown in  FIGS.  37 C-H , the channel  944  can extend between an opening  942  on an exterior surface of the enclosing body  906  and an opening  943  on the interior surface  954  of the enclosing body  906 . In some embodiments, the opening  942  is positioned on the exterior surface of the outer shell  950 . In some embodiments, the interior surface  954  is an interior surface of the liner  952  and the opening  943  is positioned on the interior surface  954 . The channel  944  can include a threaded section  947  configured to engage a threaded section of the plug  980  or a fastener. In some embodiments, at least a portion of the threaded section  947  is formed in the outer shell  950 . In some embodiments, at least a portion of the threaded section  947  is formed in the liner  952 . 
       FIGS.  38 A-K  depict views of the articulating element  904 .  FIG.  38 A  depicts a top posterior perspective view of the articulating element  904 .  FIG.  38 B  depicts a top anterior perspective view of the articulating element  904 .  FIG.  38 C  depicts a bottom posterior perspective view of the articulating element  904 .  FIG.  38 D  depicts a bottom anterior perspective view of the articulating element  904 . 
       FIG.  38 E  depicts a posterior view of the articulating element  904 .  FIG.  38 F  depicts an anterior view of the articulating element  904 .  FIG.  38 G  depicts a first sagittal view of a lateral side of the articulating element  904 .  FIG.  38 H  depicts a second sagittal view of a medial side of the articulating element  904 .  FIG.  38 I  depicts a top view of the articulating element  904 .  FIG.  38 J  depicts a bottom view of the articulating element  904 .  FIG.  38 K  depicts a cross-sectional view of the articulating element  904 . 
     As shown in  FIGS.  38 A-K , the articulating element  904  includes an articulating body  918  and an attachment member  920 . As described herein, the articulating body  918  can be at least partially positioned within and configured to move within the inner cavity  914  of the enclosing body  906 . The articulating body  918  has a superior end  922  and an inferior end  924 . 
     As shown in  FIGS.  38 A-K , the attachment member  920  can extend from the superior end  922  of the articulating body  918 . In some embodiments, the attachment member  920  can extend superiorly from the articulating body  918 . In some embodiments, the attachment member  920  can extend laterally from the articulating body  918 . In some embodiments, the attachment member  920  can extend posteriorly from the articulating body  918 . 
     In some embodiments, the attachment member  920  can include a first section  921  and a second section  923 . In some embodiments, the first section  921  can extend from the articulating body  918  in superior, lateral, and/or posterior directions. In some embodiments, the second section  923  can extend from the first section in lateral and/or anterior directions. In some embodiments, the first section  921  and the second section  923  can connect at or form a bend  925 . In some embodiments, the bend  925  can be positioned lateral to the articulating body. 
     The attachment member  920  can be shaped and/or dimensioned to facilitate securement of the facet joint replacement device  900  to the spine. As shown in  FIGS.  38 A-J , the attachment member  920  can be a rod. However, the attachment member  920  can be any shape suitable for fixation directly or indirectly to a vertebral body. In some embodiments, the attachment member  920  can have a diameter of 5.5 mm. In some embodiments, the attachment member  920  can have a diameter of 1 mm, 2 mm, 3 mm, 4 mm, 4.5 mm, 5 mm, 5.5 mm, 6 mm, 6.5 mm, 7 mm, 8 mm, 9 mm, 10 mm, between 2 mm to 8 mm, between 4 mm to 6 mm, between 5 mm to 7 mm, or between 5 mm to 6 mm. In some embodiments, the attachment member  920  can have a length of 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, between 2 mm to 8 mm, between 4 mm to 6 mm, between 5 mm to 10 mm, between 10 mm to 15 mm, between 15 mm to 20 mm, between 20 mm to 25 mm, between 25 mm to 30 mm, between 15 mm to 30 mm, or less than 15 mm. 
     As shown in  FIGS.  38 A-K , In some embodiments, a portion of an exterior surface  964  of the articulating body  918  can be shaped to form an articulating surface  926 . In some embodiments, the articulating surface  926  can be convex or at least partially convex. In some embodiments, the articulating surface  926  can be shaped/and or dimensioned to correspond to the shape, size, and/or concavity of an articular surface of a healthy inferior articular process. 
     In some embodiments, the articulating surface  926  of the articulating body and the articulating surface  928  of the enclosing body have complementary surface shapes. In some embodiments, the articulating surface  926  and the articulating surface  928  are elliptical or generally elliptical, circular or generally circular, oval or generally oval, rounded, polygonal, oblong, symmetric, asymmetric, or any other suitable shape. In some embodiments, the articulating surface  926  and articulating surface  928  can be shaped such that force is applied symmetrically to the articulating  928  when the articulating element  926  contacts or otherwise applies a force upon the articulating surface  928 . 
     As shown in  FIGS.  38 A-K , the articulating body  918  can include a slot, groove, or recess  960  extending inwardly relative to a surrounding area  962  of the exterior surface  964 . In some embodiments, the projection  956  and recess  960  can be generally concave in shape. In some embodiments, the recess  960  can be generally parabolic in shape. In some embodiments, the recess  960  can extend from an inferior portion of the articulating body to a superior portion of the articulating body  918 . In some embodiments, the articulating surface  926  can be positioned on a face of the articulating body  918  generally opposite the recess  960 . 
     As shown in  FIGS.  38 A-K , the articulating body  918  can include an opening  949  on the exterior surface  964  of the articulating body  918 . The opening  949  can be dimensioned, positioned, or otherwise configured to align with the opening  943  of the enclosing body  906  while the articulating body  918  is located at a particular position within the enclosing body  906 . As shown in  FIG.  38 J , a channel  946  extends from the opening  949  into the interior of the articulating body  918 . The channel  946  can be shaped, dimensioned, or otherwise configured to receive a fastener. In some embodiments, the channel  946  can include a threaded portion configured to couple with a threaded portion of a fastener. 
     In some embodiments, the articulating body  918  is formed of or formed partially of one or more metals or metal alloys. In some embodiments, the articulating body  918  is formed of cobalt-chrome. For example, the articulating body  918  can be formed of cobalt-chromium, titanium, titanium-based alloys, or any other suitable metals or metal alloys. In some embodiments, the articulating body  918  can be ceramic or partially ceramic. In some embodiments, the articulating body  918  can include super-hard ceramics. 
     In some embodiments, the articulating element  904  can be integrally or monolithically formed. Thus, the articulating element  904  can differ from the articulating element  704  which the attachment portion  720  is a separate component releasably or permanently coupled to the articulating body  718 . 
       FIG.  39    is an exploded view of a facet joint replacement device  900 .  FIGS.  40 A-C  depict posterior-medial cross sectional views of the facet joint replacement device  900 . 
     The articulating body  918  is configured to move within the enclosing body  906  in at least one direction. When the attachment member  920  is secured to a superior vertebral body and the attachment member  912  is secured to an inferior vertebral body, movement between the superior and inferior vertebral bodies can cause movement of the attachment member  920  with respect to the position of the enclosing body  906  resulting from the attachment member  912  being secured to the inferior vertebral body. Movement of the attachment member  920  with respect to the enclosing body  906  causes movement of the articulating body  918  within the enclosing body  906  generally along the interior surface  954  of the enclosing body  906 . 
     In certain embodiments, the articulating body  918  can move along an axis of articulation, such as axis  703  shown with respect to  FIGS.  29 A-D . The axis of articulation represents an axis of articulation of the articulating body  918  within the enclosing body  906  and/or an axis of articulation of the articulating surfaces  926  and  928  relative to one another. The articulating body  918  can be configured to move along the axis of articulation within the enclosing body. In some embodiments, the axis of articulation can be parallel with a superior-inferior anatomical axis when the facet joint replacement device  900  is implanted within a patient. In some embodiments, the axis of articulation can be parallel with an angle formed between the articulating surfaces  926  and  928 . 
     In some embodiments, the attachment member  920  is configured to move along the axis of articulation towards and away from the enclosing body  906 . When the attachment member  920  moves towards the enclosing body  906  along the axis of articulation, the attachment member  920  moves along the axis of articulation in an inferior direction. When the attachment member  920  moves away from the enclosing body  906  along the axis of articulation, the attachment member  920  moves along the axis of articulation in a superior direction. The articulating body  918  moves along the axis of articulation in the same manner when the attachment member  920  moves along the axis of articulation. Although relative movement of the attachment member  920  towards and away from the enclosing body  906  is discussed, one of skill in the art would understand that movement between the enclosing body  906  and attachment member  920  could be described as movement of the enclosing body  906  towards or away from the attachment member  920  or movement of the enclosing body  906  and attachment member  920  towards or away from each other. 
     In some embodiments, a spring coil can be positioned, for example within or as a portion of the external surface of the enclosing body  906  adjacent the inferior aspect of the device  910  of the enclosing body  906 , and/or otherwise configured such that when a threshold extension force is applied when the inferior articulating body  922  is advancing inferiorly within the enclosing body, the spring coil actuates from an initial position to decrease an angle between the attachment member  912  and the enclosing body  906  from an initial angle to a decreased angle. When the amount of force applied is no longer above the threshold extension force, the spring coil can be configured to return to the initial configuration such that the initial angle between the enclosing body and the attachment member  912  is restored. 
     Movement of the attachment member  920  with respect to the enclosing body  906  causes movement of the articulating surface  926  with respect to the articulating surface  928 . In some embodiments, movement of the attachment member  920  with respect to the enclosing body  906  causes movement of the articulating surface  926  along the axis of articulation relative to the articulating surface  928 . In some embodiments, the articulating surface  926  can be configured to articulate relative to the articulating surface  928  by moving substantially only parallel to an angle formed by the two juxtaposed articulating surfaces  926  and  978 . Although relative movement of the articulating surface  926  relative to the articulating surface  928  is discussed, one of skill in the art would understand that movement between the articulating surface  926  and the articulating surface  928  could be described as movement of the articulating surface  928  relative to the articulating surface  928  or movement of the articulating surfaces  926  and  928  relative to each other. The axis of articulation can represent the direction of relative movement between the articular surfaces of a healthy facet joint. In some embodiments, the articulating surfaces  926  and  928  can be configured to articulate relative each other by moving substantially only parallel to an angle formed by the two juxtaposed articulating surfaces  926  and  978 . 
     In some embodiments, the enclosing body  906  acts to limit relative movement between the articulating surface  926  and the articulating surface  928  along the axis of articulation. In some embodiments, the enclosing body  906  acts to limit relative movement of the articling surface  926  and articulating surface  928  perpendicular to the axis of articulation. In some embodiments, the enclosing body  906  can act to limit relative movement between the articulating surfaces  926  and  928  to correspond to the limitations of movement of the articular surfaces of a healthy facet joint. In some embodiments, the enclosing body  906  can act to limit movement between the articulating surfaces  926  and  928  to correspond to the limitations of movement provided by the facet joint capsule of a healthy facet joint. In any of the embodiments described above or elsewhere in this specification, the enclosing body can be configured to restrict movement of the articulating body within the enclosing body such that the articulating surface  926  moves only along an axis parallel with the superior/inferior axis of the patient. In some embodiments, the enclosing body  906  can be configured to restrict movement of the articulating body  918  within the enclosing body such that the articulating body  918  moves only along an axis parallel with an angle formed by the juxtaposed articulating surface  926  and articulating surface  928 . In some embodiments, the enclosing body  906  can be configured to restrict movement of the articulating body  918  within the enclosing body  906  such that the articulating surface  926  moves only along an axis parallel with an angle formed by the juxtaposed articulating surfaces  926  and  928 . 
     When the articulating body  918  moves within the enclosing body  906 , the articulating surface  926  can contact the articulating surface  928 . The articulating surface  926  can articulate against the articulating surface  928 . In some embodiments, the articulating surfaces  926  and  928  may apply an axial load to one another during articulation. In some embodiments, the outer shell  950  and/or liner  952  may have a sufficient thickness at articulating surface  928  to receive an axial load supplied by the articulating body  918  to the articulating surface  928  due to movement of the articulating body  918  within the enclosing body  906 . In some embodiments, the articulating body  918  may have a sufficient thickness at articulating surface  926  to receive an axial load supplied by the enclosing body  906  to the articulating surface  928  due to movement of the articulating body  918  within the enclosing body  906 . 
     Although articulation between the articulating surface  926  and the articulating surface  928  is discussed herein, it is contemplated that articulation between any or all of the exterior surfaces of the articulating body  918  and any or all of the interior surfaces of the enclosing body  906  could occur alternatively or in addition to articulating between the articulating surface  926  and the articulating surface  928 . 
     In some embodiments, the enclosing body  906  and articulating body  918  are configured such that a maximum distance between a center point of the articulating surface  926  and the articulating surface  928  is 0.5 mm, 1.0 mm, 1.5 mm, 1.75 mm, 2.0 mm, 2.25 mm, 2.5 mm, 3.0 mm, 3.5 mm, 4.0 mm, 5.0 mm, less than 2.0 mm, less than 3.0 mm, less than 4.0 mm, between 1.0 mm and 3.0 mm, between 1.0 mm and 2.0 mm, between 2.0 mm and 3.0 mm, between 1.5 mm and 2.5 mm, or between 1.75 mm and 2.25 mm. 
     As shown in  FIGS.  29 A-D , in some embodiments, a portion of the articulating body  918  can extend or align with the opening  1006  of the enclosing body  906 . In some embodiments, the opening  1006  is dimensioned, shaped, or otherwise configured to prevent removal of the articulating body  918  through the opening  1006 . For example, in some embodiments, at least some sections of the articulating body  918  are wider than the opening  1006 . In some embodiments, the superior end  908  can be shaped, dimensioned, or otherwise configured to prevent removal of the articulating body  918  from the enclosing body  906 . For example, in some embodiments, the retention plate  917  of the enclosing body is shaped and positioned to prevent a cross-section of at least a portion of the articulating body  918  from removal through the opening  1006 . 
     In some embodiments, the enclosing body  906  is shaped, dimensioned, or otherwise configured to circumferentially enclose the articulating surface  926  and the articulating surface  928 . In some embodiments, the enclosing body  906  encloses an entire circumferential portion of the articulating body  918  that includes the articulating surface  926 . In some embodiments, the liner  952  is shaped, dimensioned, or otherwise configured to circumferentially enclose the articulating surface  926  and the articulating surface  928 . In some embodiments, the liner  952  encloses an entire circumferential portion of the articulating body  918  that includes the articulating surface  926 . 
       FIG.  40 A  depicts the articulating body  918  at a neutral position within the enclosing body  906 . The neutral position can refer to a position in which the opening  949  and/or channel  946  of the articulating body  918  is aligned with the opening  943  and/or channel  944  of the enclosing body  906 . In some embodiments, the neutral position is a mid-position between a superior-most articulating position and an inferior-most articulating position over which the articulating body  918  can move within the enclosing body  906 .  FIG.  40 B  shows the articulating body  918  at a position superior to the neutral position within the enclosing body  906 .  FIG.  40 C  shows the articulating body  918  at a position inferior to the neutral position within the enclosing body  906 . As shown in  FIG.  40 A-C , the articulating body  918  can move along the axis of articulation within the enclosing body. In some embodiments, the articulating body  918  can move along the axis of articulation within the enclosing body while the plug  980  is positioned within the channel  944  of the enclosing body. 
     When the articulating body  918  is positioned within the enclosing body  906 , the recess  960  receives the projection  956 . In other words, the projection  956  is positioned within the recess  960 . In some embodiments, the recess  960  and the projection  956  can have complementary shapes and/or dimensions. The recess  960  and/or projection  956  can be shaped, dimensioned, or otherwise configured to prevent relative rotation of the articulating body  918  within the enclosing body  906  when the projection  956  is received within the recess  960 . The recess  960  and/or projection  956  can be shaped, dimensioned, or otherwise configured to allow relative movement between the articulating surface  926  and the articulating surface  928  along the axis of articulation. In some embodiments, the axis of articulation can be generally aligned with a longitudinal axis of the recess  960 . The recess  960  can be configured to move superiorly and inferiorly relative to the projection  956 , and/or the projection  956  can be configured to move superiorly and inferiorly within the recess  960 . 
     Although a single projection  956  and a single recess  960  are shown, any number of projections and recesses may be utilized to prevent relative rotation of the articulating body  918  within the enclosing body  906 . 
     In some embodiments, the enclosing body  906  is configured to protect the surrounding anatomy from friction, damage, or wear products due to the movement of components, including the articulating surface  926  and articulating surface  928  in the interior of the enclosing body  906 , for example, by acting as a physical barrier. For example, the enclosing body  906  can protect an adjacent thecal sac and adjacent nerve roots from involvement with the articulating surfaces  926  and  928  during relative movement between the articulating surfaces  926  and  928 . In some embodiments, the enclosing body  906  is configured to protect the components within the interior of the enclosing body  906  from damage, wear, or fibrosis due to the surrounding anatomy, for example, by acting as a physical barrier. 
       FIGS.  41 A-C  depict a top perspective, bottom perspective, and front view of the retention plate  917 . As described above, the retention plate  917  can include the base layer  1004 . The base layer  1004  can include a lip  1008  configured to be secured within the cavity  973  of the liner  952 . In some embodiments, the retention plate can include the top layer  1002  positioned superior to the base layer  1004 . In some embodiments, the top layer  1002  can having a smaller cross-sectional area than the base layer  1004 . As described above with respect to  FIGS.  37 A-B , the retention plate  917  can couple to the liner  952  and/or shell  950  to form the enclosing body. The retention plate  917  can also define the opening  1006 . 
     In certain embodiments, the facet joint replacement device  900  can be implanted in the same or similar manner and in the same or a similar location as described with respect to the facet joint replacement device  700 , for example with respect to  FIGS.  34 A-G . For example, the attachment member  920  can be affixed to the pedicle  240  of the superior vertebra or superior vertebral body  205  by the fastener  874  and the attachment member  912  can be affixed to the pedicle  242  of the interior vertebra or inferior vertebral body  210  by a fastener  876 . 
     When the facet joint replacement device  900  is implanted, the articulating surface  926  can be shaped, dimensioned, or otherwise configured to face at least partially in an anterior and lateral direction. When the facet joint replacement device  900  is implanted, the articulating surface  926  can be shaped, dimensioned, or otherwise configured to face in a direction that corresponds to that of an inferior articular surface of a healthy facet joint. When the facet joint replacement device  900  is implanted, the articulating surface  928  can be shaped, dimensioned, or otherwise configured to face at least partially in a posterior and medial direction. When the facet joint replacement device  900  is implanted, the articulating surface  928  can be shaped, dimensioned, or otherwise configured to face in a direction that corresponds to that of a superior articular surface of a healthy facet joint. In some embodiments, when the facet joint replacement device  900  is implanted, the enclosing body  906  can be located at an anatomical location corresponding to that of a healthy facet joint. In some embodiments, when the attachment member  912  is fixed relative to the inferior vertebral body and the attachment member  920  is fixed relative to the superior vertebral body, the attachment member  912  and/or the attachment member  920  can be shaped, dimensioned, or otherwise configured to locate the articulating surfaces  926  and  928  at a location corresponding to the location of the articular surfaces within the a healthy facet joint. 
     One of skill in the art would understand that a facet joint replacement device, such as facet joint replacement device  900 , can be implanted on either lateral side of a motion segment, or two facet joint replacement devices can be implanted bilaterally, one on each side of a particular motion segment, for example, as described with respect to  FIG.  12   . One of skill in the art would further understand that two facet joint replacement devices, such as facet joint replacement device  900 , can be implanted ipsilaterally, as described with respect to  FIG.  20   . 
     As described herein, the components of the facet joint replacement device  900  can be shaped and/or dimensioned to correspond to the anatomy of a healthy facet joint and related spinal motion segment. While lumbar facet joints are shown and described herein, applications of the facet joint replacement device  900  are not limited to the lumbar spine. In some embodiments, the facet joint replacement device  900  can be shaped and/or dimensioned to correspond to the anatomy of the thoracic spine. In some embodiments, a vertical distance between the superior end  908  of the enclosing body and the inferior end  910  of the enclosing body is between 20 mm to 44 mm, between 24 mm to 40 mm, between 28 mm and 36 mm, or between 30 mm and 34 mm. In some embodiments a vertical distance between the superior end  908  of the enclosing body and the inferior end  710  of the enclosing body is 28 mm, 29 mm, 30 mm, 31 mm, 32 mm, 33 mm, 34 mm, 35 mm, or 36 mm. In some embodiments, the facet joint replacement device  900  can be shaped and/or dimensioned to correspond to the anatomy of the cervical spine. 
     In some embodiments, one or both of the articulating surface  928  and articulating surface  926  can have a major axis length of 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, 16 mm, 17 mm, 18 mm, between 10 mm to 25 mm, between 9 to 14 mm, between 10 to 14 mm, or between 12 mm to 14 mm. In some embodiments, one or both of the articulating surface  128  and articulating surface  126  can have a minor axis length of 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, 16 mm, 17 mm, 18 mm, between 8 mm to 25 mm, between 8 mm to 14 mm, between 9 mm to 14 mm, or between 12 mm to 14 mm. 
       FIGS.  34 A-G  show a unilateral implantation of a facet joint replacement device  700 . One of skill in the art would understand that a facet joint replacement device, such as facet joint replacement device  700 , can be implanted on either lateral side of a motion segment, or two facet joint replacement devices can be implanted bilaterally, one on each side of a particular motion segment, for example, as described with respect to  FIG.  12   . One of skill in the art would further understand that two facet joint replacement devices, such as facet joint replacement device  700 , can be implanted ipsilaterally, as described with respect to  FIG.  20   . 
     As described herein, the components of the facet joint replacement device  700  can be shaped and/or dimensioned to correspond to the anatomy of a healthy facet joint and related spinal motion segment. While lumbar facet joints are shown and described herein, applications of the facet joint replacement device  700  are not limited to the lumbar spine. In some embodiments, the facet joint replacement device  700  can be shaped and/or dimensioned to correspond to the anatomy of the thoracic spine. In some embodiments, a vertical distance between the superior end  708  of the enclosing body and the inferior end  710  of the enclosing body is between 20 mm to 44 mm, between 24 mm to 40 mm, between 28 mm and 36 mm, or between 30 mm and 34 mm. In some embodiments a vertical distance between the superior end  708  of the enclosing body and the inferior end  710  of the enclosing body is 28 mm, 29 mm, 30 mm, 31 mm, 32 mm, 33 mm, 34 mm, 35 mm, or 36 mm. In some embodiments, the facet joint replacement device  700  can be shaped and/or dimensioned of correspond to the anatomy of the cervical spine. 
     In some embodiments, one or both of the articulating surface  128  and articulating surface  126  can have a major axis length of 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, 16 mm, 17 mm, 18 mm, between 10 mm to 25 mm, between 9 to 14 mm, between 10 to 14 mm, or between 12 mm to 14 mm. In some embodiments, one or both of the articulating surface  128  and articulating surface  126  can have a minor axis length of 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, 16 mm, 17 mm, 18 mm, between 8 mm to 25 mm, between 8 mm to 14 mm, between 9 mm to 14 mm, or between 12 mm to 14 mm. 
     As shown in  FIG.  35    with respect to facet joint replacement device  700 , the axis  790  parallel to a sagittal anatomic plane can extend through a center point of the articulating surface  926 , the axis  792  parallel to a frontal anatomic plane can extend through a center point of the articulating surface  926 , and the axis  794  can extending through the center point of the articulating surface  926  and perpendicular to a tangent of the articulating surface  926  at the center point. As described above, an angle α extends between the axis  790  and the axis  794 . An angle β extends between the axis  792  and  794 . In some embodiments, the angle α can be between 30° and 60°, between 35° and 55°, between 40° and 50°, or any other suitable range. In some embodiments, the angle α can be 30°, 35°, 40°, 45°, 50°, 55°, 60°, or any other suitable angle. In some embodiments, the angle β can be between 30° and 60°, between 35° and 55°, between 40° and 50°, or any other suitable range. In some embodiments, the angle θ can be 30°, 35°, 40°, 45°, 50°, 55°, 60°, or any other suitable angle. In some embodiments, an angle between an axis extending through the center point of the articulating surface  926  parallel to a transverse anatomic plane and the axis  794  can be between 75° and 105°, between 80° to 100°, between 85° to 95° or any other suitable angle. In some embodiments, an angle between an axis extending through the center point of the articulating surface  926  parallel to a transverse anatomic plane and the axis  794  can be 75°, 80°, 85°, 90°, 95°, 100°, 105° or any other suitable angle. 
     Similarly, in some embodiments, an angle between an axis parallel to a frontal anatomic plane and extending through a center point of the articulating surface  928  and an axis extending through the center point of the articulating surface  928  and perpendicular to a tangent of the articulating surface  928  at the center point can be between 30° and 60°, between 35° and 55°, between 40° and 50°, or any other suitable range. In some embodiments, an angle between an axis parallel to a frontal anatomic plane and extending through a center point of the articulating surface  928  and an axis extending through the center point of the articulating surface  928  and perpendicular to a tangent of the articulating surface  928  at the center point can be 30°, 35°, 40°, 45°, 50°, 55°, 60°, or any other suitable angle. In some embodiments, an angle between an axis parallel to a sagittal anatomic plane and extending through a center point of the articulating surface  928  and an axis extending through the center point of the articulating surface  928  and perpendicular to a tangent of the articulating surface  928  at the center point can be between 30° and 60°, between 35° and 55°, between 40° and 50°, or any other suitable range. In some embodiments, an angle between an axis parallel to a sagittal anatomic plane and extending through a center point of the articulating surface  928  and an axis extending through the center point of the articulating surface  928  and perpendicular to a tangent of the articulating surface  928  at the center point can be 30°, 35°, 40°, 45°, 50°, 55°, 60°, or any other suitable angle. In some embodiments, an angle between an axis parallel to a transverse anatomic plane and extending through a center point of the articulating surface  928  and an axis extending through the center point of the articulating surface  928  and perpendicular to a tangent of the articulating surface  728  at the center point can be between 75° and 105°, between 80° to 100°, between 85° to 95° or any other suitable angle. In some embodiments, an angle between an axis parallel to a transverse anatomic plane and extending through a center point of the articulating surface  728  and an axis extending through the center point of the articulating surface  928  and perpendicular to a tangent of the articulating surface  928  at the center point can be 75°, 80°, 85°, 90°, 95°, 100°, 105°, or any other suitable angle. 
     In some embodiments, the axis of articulation can be perpendicular to a transverse anatomic plane. In some embodiments, the axis of articulation can be parallel to a sagittal anatomic plane. In some embodiments, the axis of articulation can be parallel to a frontal anatomic plane. 
     As described herein, in some embodiments, the implant  900  can be shaped and/or dimensioned to correspond to the anatomy of the lumbar spine, thoracic spine, or cervical spine. 
     In some embodiments, an angle between the transverse anatomic plane and a mean orientation of the articulating surface  926  can be between 0° and 98°, between 10° and 88°, between 20° and 78°, or any other suitable angle for a facet joint replacement device  700  implanted within the cervical spine. In some embodiments, an angle between the transverse anatomic plane and a mean orientation of the articulating surface  926  can be between 35° and 100°, between 45° and 90°, between 55° and 80°, or any other suitable angle for a facet joint replacement device  900  implanted within the thoracic spine. In some embodiments, an angle between the transverse anatomic plane and a mean orientation of the articulating surface  926  can be between 62° and 106°, between 72° and 96°, between 82° and 86°, or any other suitable angle for a facet joint replacement device  900  implanted within the lumbar spine. In some embodiments, the transverse anatomic plane may be referred to as the 0° transverse plane. In some embodiments, the foregoing angles between the transverse anatomic plane and a mean orientation of the articulating surface  926  may be referred to as inclination angles of the articulating surface  926  within the sagittal anatomic plane. 
     In some embodiments, an angle between the sagittal anatomic plane and a mean orientation of the articulating surface  926  can be between 50° and 116°, between 60° and 106°, between 70° and 96°, or any other suitable angle for a facet joint replacement device  700  implanted within the cervical spine. In some embodiments, an angle between the sagittal anatomic plane and a mean orientation of the articulating surface  926  can be between 65° and 140°, between 75° and 130°, between 85° and 120°, or any other suitable angle for a facet joint replacement device  700  implanted within the thoracic spine. In some embodiments, an angle between the sagittal anatomic plane and a mean orientation of the articulating surface  926  can be between 0° and °  90 , between 5° and 80°, between 15° and 70°, or any other suitable angle for a facet joint replacement device  900  implanted within the lumbar spine. In some embodiments, the sagittal anatomic plane may be referred to as the 0° sagittal plane. In some embodiments, the foregoing angles between the sagittal anatomic plane and a mean orientation of the articulating surface  926  may be referred to as inclination angles of the articulating surface  926  within the transverse anatomic plane. 
     In some embodiments, the articulating surface  926  can be configured to articulate relative to the articulating surface  928  by moving substantially only parallel to an axis defined by the inclination angles of the articulating surface  926  within the sagittal and transverse anatomic planes. 
     In some embodiments, an angle between the transverse anatomic plane and a mean orientation of the articulating surface  928  can be between 0° and 98°, between 10° and 88°, between 20° and 78°, or any other suitable angle for a facet joint replacement device  900  implanted within the cervical spine. In some embodiments, an angle between the transverse anatomic plane and a mean orientation of the articulating surface  928  can be between 35° and 100°, between 45° and 90°, between 55° and 80°, or any other suitable angle for a facet joint replacement device  900  implanted within the thoracic spine. In some embodiments, an angle between the transverse anatomic plane and a mean orientation of the articulating surface  928  can be between 62° and 106°, between 72° and 96°, between 82° and 86°, or any other suitable angle for a facet joint replacement device  900  implanted within the lumbar spine. In some embodiments, the transverse anatomic plane may be referred to as the 0° transverse plane. In some embodiments, the foregoing angles between the transverse anatomic plane and a mean orientation of the articulating surface  928  may be referred to as inclination angles of the articulating surface  928  within the sagittal anatomic plane. 
     In some embodiments, an angle between the sagittal anatomic plane and a mean orientation of the articulating surface  928  can be between 50° and 116°, between 60° and 106°, between 70° and 96°, or any other suitable angle for a facet joint replacement device  900  implanted within the cervical spine. In some embodiments, an angle between the sagittal anatomic plane and a mean orientation of the articulating surface  928  can be between 65° and 140°, between 75° and 130°, between 85° and 120°, or any other suitable angle for a facet joint replacement device  700  implanted within the thoracic spine. In some embodiments, an angle between the sagittal anatomic plane and a mean orientation of the articulating surface  728  can be between 0° and °  90 , between 5° and 80°, between 15° and 70°, or any other suitable angle for a facet joint replacement device  900  implanted within the lumbar spine. In some embodiments, the sagittal anatomic plane may be referred to as the 0° sagittal plane. In some embodiments, the foregoing angles between the sagittal anatomic plane and a mean orientation of the articulating surface  928  may be referred to as inclination angles of the articulating surface  928  within the transverse anatomic plane. 
     In some embodiments, the articulating surface  928  can be configured to articulate relative to the articulating surface  926  by moving substantially only parallel to an axis defined by the inclination angles of the articulating surface  928  within the sagittal and transverse anatomic planes. 
       FIGS.  42 A-F  depict a device holder  1040  according to one embodiment.  FIG.  42 A  depicts a perspective view of the device holder  1040 .  FIG.  42 B  depicts a front view of the device holder  1040 .  FIG.  42 C  depicts a side view of the device holder  1040 . 
     As shown in  FIGS.  42 A-C , in some embodiments, the device holder  1040  can include a handle  1042 . In some embodiments, the handle  1042  can be shaped, dimensioned, and/or otherwise configured to be grasped and manipulated by a user. 
     In some embodiments, the device holder can include a fastener or fastening head  1046 . In some embodiments, the device holder  1040  can include a shaft  1044 . The shaft  1044  can extend between the handle  1042  and the fastening head  1046 . 
       FIG.  42 D  depicts a top perspective enlarged view of a portion of the device holder  1040  showing the fastening head  1046 .  FIG.  42 E  depicts a bottom perspective enlarged view of a portion of the device holder  1040  showing the fastening head  1046 . 
     As shown in  FIGS.  42 D-E , the fastening head  1046  can include an externally threaded portion  1048 , a generally cylindrical portion  1050 , and a tip  1052 . In some embodiments, the fastening head  1046  can have generally the same or similar shape as the fastener  740 . In some embodiments, the fastening head  1046  can include any of the same features or functions as the fastener  740 . In some embodiments, the fastening head  1046  can be used for any of the uses of the fastener  740  described herein. 
     In some embodiments, the device holder  1040  can be configured to couple to a facet joint replacement device such as facet joint replacement device  700  or facet joint replacement device  900 .  FIG.  42 F  depicts a perspective view of the device holder  1040  coupled to the facet joint replacement device  900 .  FIG.  42 G  depicts an enlarged cross-sectional view of a portion of the device holder  1040  coupled to the facet joint replacement device  900 . 
     As shown in  FIG.  42 G , the fastening head  1046  can be received within the channels  944  and  946  of the enclosing body  906  and articulating element  918 . As shown in  FIG.  42 G , the externally threaded section  1048  of the fastening head  1046  can removably secure to the internally threaded section  947  of the channel  944 . In some embodiments, the externally threaded section  1048  of the fastening head  1046  can removably secure to an internally threaded section of the channel  946 . In some embodiments, the handle  1042  can be used to apply torque to the fastening head  1046  to thread and unthread the threaded section  1048  of the fastening head  1046  with the internally threaded section  947  of the channel  944  or with an internally threaded section of the channel  946 . When positioned within the channels  944  and  946 , the fastening head  1046  can prevent movement of the articulating body  918  relative to the enclosing body  906 . When positioned within the channels  944  and  946 , the fastening head  1046  can maintain the articulating body  918  at the neutral position within the channels  944  and  946 . 
     In some embodiments, the device holder  1040  or one or more components of the device holder  1040 , such as the handle  1042 , the shaft  1044 , and the fastening head  1046 , can be formed of or formed partially of one or more metals or metal alloys. For example, the device holder  1040  or one or more components of the device holder  1040 , such as the handle  1042 , the shaft  1044 , and the fastening head  1046 , can be formed of cobalt-chromium, titanium, titanium-based alloys, stainless steel, or any other suitable metals or metal alloys. In some embodiments, the device holder  1040  or one or more components of the device holder  1040 , such as the handle  1042 , the shaft  1044 , and the fastening head  1046 , can be ceramic or partially ceramic. In some embodiments, the device holder  1040  or one or more components of the device holder  1040 , such as the handle  1042 , the shaft  1044 , and the fastening head  1046 , can include super-hard ceramics. 
     In some embodiments, the device holder  1040  can be coupled to a facet joint replacement device, such as the facet joint replacement devices  700  and  900  at the time of manufacturing, prior to shipping the facet joint replacement device, or prior to installation of the facet joint replacement device to prevent movement of an articulating body, such has articulating bodies  718  and  918 , within an enclosing body, such as enclosing bodies  706  and  906 . The implant holder  1040  can also be used to position the facet joint replacement device within the body, for example, by a user manipulating the handle  1042 . The facet joint replacement device can be secured within the body, for example, using fasteners such as fasteners  874  and  876 , while the implant holder  1040  is coupled to the facet joint replacement device. After the facet joint replacement device is secured, the handle  1042  can be manipulated to unthread the threaded portion  1048  from the facet joint replacement device and remove the device holder  1040  from the surgical site. 
       FIGS.  43 A-D  depict an embodiment of a plug assembly  1020 .  FIG.  43 A  is a top perspective view of the plug assembly  1020 .  FIG.  43 B  is a bottom perspective view of the plug assembly  1020 .  FIG.  43 C  is a first enlarged cross-sectional view of the plug assembly  1020 .  FIG.  43 D  is a second enlarged cross-sectional view of the plug assembly  1020  showing the plug assembly  1020  separated into two pieces. 
     In some embodiments, the plug assembly  1020  includes the plug  980  described herein with respect to  FIGS.  33 A- 33 D . In some embodiments, the plug assembly  1020  can include a plug insertion section  1022 . The plug insertion section  1022  and the plug  980  can be coupled at a joint or connection  1028 . In some embodiments, the plug insertion section  1022  and the plug  980  are integrally formed. In some embodiments, the connection  1028  is a frangible connection. The connection  1028  can be configured to break, shear, tear, and/or otherwise separate in response to application of a force to the plug assembly  1020 , such as for example, a rotational force. In some embodiments, the connection  1028  can be configured to break, shear, tear, and/or otherwise separate in response to application of a force to the plug insertion section  1022 , such as for example, a rotational force. In some embodiments, the connection  1028  can be configured to break, shear, tear, and/or otherwise separate in response to application of a force to the plug insertion section  1022 , such as for example, a rotational force, while the plug  980  is maintained in a fixed position. As shown in  FIG.  43 D , the plug assembly  1020  can be separated at the connection  1028  so that the plug  980  is separated from the plug insertion section  1022 . 
     In some embodiments, a channel  1024  can extend through the plug insertion section  1022  and at least partially into the plug  980 . In some embodiments, the plug insertion section  1022  can include an internally threaded portion  1024 . 
     In certain embodiments, the plug assembly  1020  can be configured to receive a tool or instrument for inserting the plug  980  into a facet joint replacement device, such as facet joint replacement device  700  and facet joint replacement device  900 . For example, in certain embodiments, the threads  1026  can be configured to engage with corresponding threads of an instrument or tool for inserting the plug  980  into a facet joint replacement device. 
     In some embodiments, the plug assembly  1020  can be configured to couple with the device holder  1040 . In some embodiments, the device holder  1040  can be a plug inserter.  FIG.  44 A  depicts a perspective view of the device holder  1040  coupled to the plug insertion portion  1020 .  FIG.  44 B  depicts an enlarged cross-sectional view showing a portion of the device holder  1040  coupled to the plug assembly  1020 .  FIG.  44 C  is a front view showing the device holder  1040  coupled to the plug insertion portion  1022  after separation of the plug insertion portion  1022  from the plug  980 . 
     In some embodiments, as shown in  FIG.  44 B , in some embodiments, the plug assembly  1020  can be configured to receive the fastening head  1046  of the device holder  1040  within the channel  1024 . In some embodiments, the internal threads  1026  of the plug insertion section  1022  can be configured to mate with the external threads  1048  of the fastening head  1046 . 
     In certain embodiments, the plug  980  can be used in the same or a similar fashion as the plug  780  described herein. For example, the plug  980  can be positioned within the channel  744  of the facet joint replacement device  700  as shown in  FIGS.  33 C-D . The plug  980  can similarly be positioned within the channel  944  of the facet joint replacement device  900 . 
     The externally threaded section  981  of the plug  980  can removably secure to the internally threaded section  747  of the channel  744  or the internally threaded section  947  of the channel  944 . In some embodiments, the plug is shaped, dimensioned, or otherwise configured to extend through only a portion of the channel  744  or  944 . The plug  980  can be dimensioned, shaped, or otherwise configured such that when the plug  980  is positioned within the facet joint replacement device  700  or  900 , the plug  980  does not extend into the channel  746  or  946 . When the plug  980  is positioned within the facet joint replacement device  700  or  900 , the plug  980  does not restrict movement of the articulating body  718  or  918  within the enclosing body  706  or  906 . In some embodiments, the plug  980  is shaped, dimensioned, or otherwise configured to fit flush with an exterior surface of the enclosing body  706  or  906 . 
     When positioned within the enclosing body  706  or  906 , the plug  980  can seal the opening  742  or  942  and/or channel  744  or  944  relative to the surrounding anatomy. By sealing the opening  742  or  942  and/or channel  744  or  944 , the plug  980  can act as a physical barrier along with enclosing body  706  or  906  to protect the surrounding anatomy from friction, damage, or infection due to the movement of components, including the articulating surface  726  or  926  and articulating surface  728  or  928  in the interior of the enclosing body  706  or  906 . For example, the enclosing body  706  or  906  and plug  980  can protect an adjacent thecal sac and adjacent nerve roots from involvement with the articulating surfaces  726  and  728  or  926  and  928  during relative movement between the articulating surfaces  726  and  728  or  026  and  028 . In some embodiments, the plug  980  and enclosing body  706  or  906  are configured to protect the components within the interior of the enclosing body  706  from damage, wear, or fibrosis due to the surrounding anatomy, for example, by acting as a physical barrier. 
     In certain embodiments, the device holder  1040  can be used to position the plug  980  within a facet joint replacement device, such as facet joint replacement devices  700  and  900 , while the plug assembly  1020  is coupled to the device holder  1040 . In some embodiments, the handle  1042  can be manipulated to thread the externally threaded section  981  of the plug  980  with the internally threaded section  747  of the channel  744  or the internally threaded section  947  of the channel  944 . In some embodiments, after the externally threaded section  981  of the plug  980  is mated with the internally threaded section  747  of the channel  744  or the internally threaded section  947  of the channel  944 , the handle  1042  can be used to turn the plug assembly  1020  in the same direction as used for mating the externally threaded section  981  of the plug  980  with the internally threaded section  747  of the channel  744  or the internally threaded section  947  of the channel  944  to apply a shearing force to the connection  1028  to cause the plug insertion section  1022  to shear off from the plug  980  as shown in  FIG.  44 C . After the plug insertion section  1022  is disconnected from the plug  980 , the insertion section  1022  can be removed from the body by removing the device holder  1040 . 
     As shown herein, in some embodiments, a fastening head  1046  can be used as both a fastener to prevent movement of the articulating element  918  within the enclosing body  906  and as a plug inserter. In other embodiments, the device holder  1040  may include a first end having a first fastening head  1046  for use a fastener to prevent movement of the articulating element  918  within the enclosing body  906  and a second end having a second fastening head  1046  for use as a plug inserter. Such an embodiment may be beneficial if different threading patterns are required to mate with the threaded sections of the plug assembly  1020  and the facet joint replacement device  900 . 
     In some embodiments, facet joint replacement devices  900  may be available in a plurality of different sizes.  FIG.  45 A  depicts a posterior view of a facet joint replacement device  900 A having a first size.  FIG.  45 B  depicts a posterior view of an articulating element  904 A of the facet joint replacement device  900 A.  FIG.  45 C  depicts a posterior view of a facet joint replacement device  900 B having a second size greater than the first size of  FIGS.  45 A-B .  FIG.  45 D  depicts a posterior view of an articulating element  904 B of the facet joint replacement device  900 B.  FIG.  45 E  depicts a posterior view of a facet joint replacement device  900 C having a third size greater than the second size of  FIGS.  45 C-D .  FIG.  45 F  depicts a posterior view of an articulating element  904 C of the facet joint replacement device  900 C. 
     As shown in  FIGS.  45 A-F , the facet joint replacement devices  900 A-C can include generally the same or similar components as the facet joint replacement device  900 . For example, the facet joint replacement devices  900 A-C include attachments members  920 A-C, enclosing elements  902 A-C, enclosing bodies  906 A-C, attachment members  912 A-C, shells  950 A-C, lines  952 A-C, superior ends  908 A-C, inferior ends  910 A-C, channels  944 A-C, first sections  911 A-C, second sections  913 A-C, bends  915 A-C, openings  949 A-C, first sections  921 A-C, second sections  923 A-C, bends  925 A-C, superior ends  922 A-C, inferior ends  924 A-C, recesses  960 A-C, surrounding areas  962 A-C, and exterior surfaces  964 A-C, as shown in  FIGS.  45 A-F . The components of the facet joint replacement devices  900 A-C can have generally the same or similar features or functions as those of the facet joint replacement device  900 . 
     In some embodiments, a distance between the superior end of the attachment member  920 A and the inferior end of the attachment member  912 A can be between 20 mm and 27 mm, 21 mm to 26 mm, 22 mm to 25 mm, 23 mm to 24 mm, or any other suitable range when the articulating body  918 A is in the neutral position. In some embodiments, the distance between the superior end of the attachment member  920 A and the inferior end of the attachment member  912 A can be 20 mm, 21 mm, 22 mm, 23 mm, 23.5 mm, 24 mm, 25 mm, 26 mm, 27 mm, or any other suitable distance when the articulating body  918 A is in the neutral position. 
     In some embodiments, a distance between the superior end of the attachment member  920 B and the inferior end of the attachment member  912 B can be between 25 mm and 32 mm, 26 mm to 31 mm, 27 mm to 30 mm, 28 mm to 29 mm, or any other suitable range when the articulating body  918 B is in the neutral position. In some embodiments, the distance between the superior end of the attachment member  920 B and the inferior end of the attachment member  912 B can be 25 mm, 26 mm, 27 mm, 28 mm, 28.5 mm, 29 mm, 30 mm, 31 mm, 32 mm, or any other suitable distance when the articulating body  918 B is in the neutral position. 
     In some embodiments, a distance between the superior end of the attachment member  920 C and the inferior end of the attachment member  912 C can be between 30 mm and 37 mm, 31 mm to 36 mm, 32 mm to 35 mm, 33 mm to 34 mm, or any other suitable range when the articulating body  918 C is in the neutral position. In some embodiments, the distance between the superior end of the attachment member  920 C and the inferior end of the attachment member  912 C can be 30 mm, 31 mm, 32 mm, 33 mm, 33.5 mm, 34 mm, 35 mm, 36 mm, 37 mm, or any other suitable distance when the articulating body  918 C is in the neutral position. 
     In some embodiments, a distance between the superior end of the attachment member  920 B and the inferior end of the attachment member  912 B can be 5 mm or about 5 mm greater than a distance between the superior end of the attachment member  920 A and the inferior end of the attachment member  912 A, when the articulating bodies  918 A and  918 B are in the neutral position. 
     In some embodiments, a distance between the superior end of the attachment member  920 C and the inferior end of the attachment member  912 C can be 5 mm or about 5 mm greater than a distance between the superior end of the attachment member  920 B and the inferior end of the attachment member  912 B, when the articulating bodies  918 B and  918 C are in the neutral position. 
     In some embodiments, the shape and size of the enclosing element  902 A can be the same or generally the same shape and size as the enclosing element  902 B except that the attachment member  912 A extends from the enclosing body  906 A at a position superior to a position at which the attachment member  912 B extends form the enclosing body  906 B, for example at a position 5 mm or about 5 mm superior to the position at which the attachment member  912 B extends from the enclosing body  906 B. 
     In some embodiments, the shape and size of the enclosing element  902 B and the enclosing element  902 C can be the same or generally the same, and the attachment member  920 C can extend a greater distance from the superior end  922 C of the articulating body  906 C than the attachment member  920 B extends from the superior end  922 B of the articulating body  906 B. For example, in some embodiments, the attachment member  920 C can extend a distance 5 mm or generally 5 mm farther from the superior end  922 C of the articulating body  906 C than the attachment member  920 B extends from the superior end  922 B of the articulating body  906 B. 
     In some embodiments, a method for implanting facet joint replacement device  700  or  900  into a patient begins with the administration of general endotracheal anesthesia. Following the administration of anesthesia, the patient is placed into a prone position and intraoperative fluoroscopy is used to identify a desired location for making a skin incision for implanting the facet joint replacement device  700  or  900 . After the desired location is selected, a midline lumbar-sacral incision is made at the desired location, and subperiosteal dissection is utilized to expose a desired lamina, facet joint, and entry points to cannulate the ipsilateral pedicles of the superior and inferior vertebral bodies associated with the facet joint to be replaced. In some alternative embodiments, minimally invasive surgical techniques can be employed for exposure of the desired lamina, facet joint, and entry points to cannulate the ipsilateral pedicles. After exposure of the desired structures, intraoperative fluoroscopy is utilized to confirm desired levels of exposure. After the desired levels of exposure are confirmed, a self-retaining retractor system is placed to maintain the desired level of exposure. 
     After the retractor system is in place, removal of one or more sections of the facet joint and surrounding bone is performed. In some embodiments, the lamina or portion of the lamina in the motion region to be treated is removed. Removal can be performed using bone biters, angled curets, and/or bone punches. In some embodiments, a ligamentum flavum or a portion of the ligamentum flavum in the motion segment to be treated is removed. Removal of the ligamentum flavum can be performed using bone punches. The facet joint or a portion of the facet joint to be treated is also removed. Removal of the facet joint can be performed using a high speed drill, bone biters, and/or bone punches. After removal of the facet joint to be treated, further decompression of the lateral recess can be performed and adjacent nerve roots can be identified. Additional bone may be removed as necessary to prevent mechanical compression of the nerve roots. 
     Following removal of the desired bone, the pedicles of the superior vertebral body and inferior vertebral body of the motion segment to be treated and desired points of entry to cannulate the pedicles are identified, for example, using intraoperative fluoroscopy. A high speed drill or bone awl is then used to perforate the cortical bone overlying the optimal entry points to cannulate each of the pedicles. The pedicles are then probed and tapped under fluoroscopic guidance. Tulip head bone screws, such as the tulip head bone screws of fasteners  874  and  876 , are then screwed into the previously tapped pedicles. Additional fixation augmentors, such as methylmethacrylate, can also be used. In some embodiments, a decision to use additional fixation augmentors is made based on apparent bone quality at the time of bone screw insertion. Methylmethacrylate or other fixation augmentors can be placed within the cannulated pedicle prior to placement of the bone screw, for example, to improve the fixation of the bone screw within the implanted pedicle bone. 
     After fixation of the bone screws to the superior and inferior vertebral bodies, the attachment member  720  or  920  can be placed within a receiving portion of the tulip head portion of the bone screw in the superior vertebral body, and the attachment member  712  or  912  can be placed within a receiving portion of the tulip head portion of the bone screw in the inferior vertebral body. After the attachment member  720  or  920  and attachment member  712  or  912  are received within the tulip head portions of the implanted bone screws, the attachment member  720  or  920  and attachment member  712  or  912  can be secured to the bone screws by fixation of top loading set screws to each of the tulip head portions of the implanted bone screws. 
     In some embodiments, after ensuring that the implanted bone screws are in proper position and secure, but before the attachment members  720  and  712  or  920  and  912  are placed into the bone screws, distraction or compression can be applied between the implanted bone screws to address any asymmetric loss of the disc space height or malalignment. 
     In some embodiments, facet joint replacement devices  700  or  900  may be available in a plurality of different sizes, as described herein with respect to  FIGS.  45 A-F . In such embodiments, after implantation of the tulip head bone screws into the superior and inferior vertebral bodies, a distance is measured between the tulips head portions of the bone screws and a facet joint replacement device can be selected based on the distance measured between the tulip head portions of the bone screws, for example, so that the attachment members of the facet joint replacement device can be securely engaged with the tulip head portions of the implanted bone screws. 
     In some embodiments, facet joint replacement devices  700  or  900  may be available with articulating surfaces having a plurality of different angular orientations with respect to the sagittal, transverse, and/or frontal anatomic planes, as described further herein. In such embodiments, after implantation of the tulip head bone screws into the superior and inferior vertebral body, a facet joint replacement device is selected based on the desired angular orientations of the articulating surfaces. The desired angular orientations can be selected based on estimated angular orientations of the articular surfaces of a healthy facet joint in the treated motion segment. 
     In some embodiments, methods of implanting the facet joint replacement device  700  or  900  include securing the articulating body  718  or  918  in a desired position within the enclosing body  706  or  906 , such as the neutral position, prior to implantation in the body using the fastener  740  or the device holder  1040 . In some embodiments, methods of implanting the facet joint replacement device  700  or  900  include positioning the articulating body  716  or  916  within the enclosing body at a desired position, such as the neutral position, prior to positioning the fastener  740  or the fastening head  1046  in the channel  744  or  944  and the channel  746  or  946 . 
     In some embodiments, methods of implanting the facet joint replacement device  700  or  900  include introducing the facet joint replacement device  700  or  900  into the body while the fastener  740  or fastening head  1046  is positioned within the channel  744  or  944  and the channel  746  or  946  to constrain movement of the articulating body in the enclosing body. In some embodiments, introducing the facet joint replacement device  700  or  900  into the body while the fastener  740  or fastening head  1046  is positioned within the channels  744  and  746  or  944  and  946  can maintain the articulating body  718  or  918  in a desired position within the enclosing body  706  or  906 , such as the neutral position, during implantation in the body using the fastener  740  or the fastening head  1046 . 
     In some embodiments, methods of implanting the facet joint replacement device  700  or  900  include securing the facet joint replacement device  700  or  900  relative to a superior vertebral body and relative to an inferior vertebral body of the patient while the fastener  740  or fastening head  1046  is positioned within the channel  744  or  944  and the channel  746  or  946  to constrain movement of the articulating body  718  or  918  within the enclosing body  706  or  906 , for example, to maintain the articulating body  718  or  918  in a desired position within the enclosing body  706  or  906 , such as the neutral position. 
     In some embodiments, the fastener  740  can remain positioned within the facet joint replacement device  700  following implantation. In some embodiments, the fastener  740  or fastening head  1046  can be removed after the facet joint replacement device  700  or  900  is secured to the spine to allow for movement of the articulating body  718  or  918  within the enclosing body  706  or  906 . In some embodiments, the fastener  740  or fastening head  1046  can be removed from the channel  744  or  944  and the channel  746  or  946  after securing the facet joint replacement device  700  or  900  relative to the superior vertebral body and relative to the inferior vertebral body to allow movement of the articulating body  718  or  918  within the enclosing body  706  or  906 . In some embodiments in which removal of the fastener or fastening head  1046  is required, the device holder  1040  may provide the benefit of preventing a surgeon from leaving the fastening head  1046  within the facet joint replacement device  900  due to the shaft  1044  and handle  1042  extending out of the body. 
     In some embodiments, after removal of the facet joint replacement device  700  or  900 , the plug  780  or  980  can be positioned within the opening  742  or  942  and channel  744  or  944 . For example, in some embodiments, the plug  980  can be positioned within the opening  742  or  942  and channel  744  or  944  using the device holder  1040 . In some embodiments, the fastening head  1046  can be coupled to the device plug assembly  1020 . When the plug assembly  1020  is coupled to the fastening head  1046 , the device holder  1040  can be used to position the plug  980  within the opening  742  or  942  and the channel  744  and  944 . After the plug  980  is positioned within the opening  742  or  942  and the channel  744  and  944 , the device holder  1040  can be used to apply a shearing force to separate the plug insertion section  1022  from the plug  980  so that the plug  980  remains within the opening  742  or  942  and the channel  744  and  944 , and the plug insertion section is removed using the device holder  1040 . 
     As described herein, when positioned within the enclosing body  706  or  906 , the plug  780  or  980  can seal the opening  742  or  942  and/or channel  744  or  944  relative to the surrounding anatomy. By sealing the opening  742  or  942  and/or channel  744  or  944 , the plug  780  or  980  can act as a physical barrier along with enclosing body  706  or  906  to protect the surrounding anatomy from friction, damage, or infection due to the movement of components, including the articulating surface  726  or  926  and articulating surface  728  or  928  in the interior of the enclosing body  706  or  906 . For example, the enclosing body  706  or  906  and plug  780  or  980  can protect an adjacent thecal sac and adjacent nerve roots from involvement with the articulating surfaces  726  or  926  and  728  or  928  during relative movement between the articulating surfaces  726  or  926  and  728  or  928 . In some embodiments, the plug  780  or  980  and enclosing body  706  or  906  are configured to protect the components within the interior of the enclosing body  706  or  906  from damage, wear, or fibrosis due to the surrounding anatomy, for example, by acting as a physical barrier. In combination, the fastener  740  or fastening head  1046  and the plug  780  or  980  can be used to restrict relative movement of the articulating surfaces  726  and  728  or articulating surfaces  926  and  928  during implantation and allow movement of the articulating surfaces after implantation while maintaining a physical barrier to the surrounding anatomy. 
     While this invention has been particularly shown and described with reference to embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention. For all of the embodiments described above, the steps of the methods need not be performed sequentially. 
     Language of degree used herein, such as the terms “approximately,” “about,” “generally,” and “substantially” as used herein represent a value, amount, or characteristic close to the stated value, amount, or characteristic that still performs a desired function or achieves a desired result. For example, the terms “approximately”, “about”, “generally,” and “substantially” may refer to an amount that is within less than 10% of, within less than 5% of, within less than 1% of, within less than 0.1% of, and within less than 0.01% of the stated amount. As another example, in certain embodiments, the terms “generally parallel” and “substantially parallel” refer to a value, amount, or characteristic that departs from exactly parallel by less than or equal to 15 degrees, 10 degrees, 5 degrees, 3 degrees, 1 degree, 0.1 degree, or otherwise. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. Thus, it is intended that the present invention cover modifications and variations of this invention.