Patent Publication Number: US-2020297509-A1

Title: Adjustable total disc replacement device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. Nonprovisional patent application Ser. No. 15/858,854 filed on Dec. 29, 2017, which is a continuation of U.S. Nonprovisional patent application Ser. No. 14/959,951 filed on Dec. 4, 2015, which claims priority to U.S. Provisional Patent Application No. 62/087,612 filed on Dec. 4, 2014, the disclosures of which are incorporated entirely herein by reference. 
    
    
     BACKGROUND 
     Technical Field 
     This invention relates to artificial intervertebral joints. In particular, the invention relates to artificial implantable intervertebral disc joints with controls for adjustable positioning of surfaces related to load-bearing and force-distribution 
     State of the Art 
     The spinal column is a segmental chain of vertebrae. Each vertebra comprises an anterior, roughly cylindrical vertebral body and posterior elements forming bony canal surrounding the spinal cord and spinal nerve roots. The posterior bony canal components of each vertebra articulate with adjoining vertebra above and below at facet joints forming a load-bearing structure known as the posterior column. The anterior vertebral bodies, in turn, articulate at intervertebral disc joints collectively forming the load-bearing structure known as the anterior column. In humans and other animals, axial loads are distributed between the anterior and posterior columns. Motion at the facet joints affects load distribution forces in both columns and, similarly, motion at the intervertebral disc joints also affects load distribution forces in both columns. 
     The human intervertebral disc (“IVD”) is a soft-tissue structure sandwiched between the bony end-plates of the vertebral body above (cranial) and the vertebral body below (caudal). This soft-tissue disc comprises a fibrous ring-shaped wall of tissue (anulusus fibrosis) surrounding a gelatinous core (nucleus pulposis.) The natural IVD space allow for motion in the anterior-posterior plane, such as flexion and extension; lateral motion to either side, and axial rotation. The human IVD joint has a non-fixed, mobile center of rotation (“COR”), or collection of multiple CORs otherwise known as a centrode, about which axial rotation occurs. 
     The IVD joint is vulnerable to a variety of degenerative processes, of both traumatic and non-traumatic etiologies, which are sometimes treated by surgically replacing the IVD joint with a prosthetic device. Available prosthetic devices, however, are limited in capacity to reproduce the natural load-bearing mechanics and range of motion of the native IVD joint. 
     Accordingly, what is needed is a device that provides a structure and mechanism of reproducing a more natural range of motion of an IVD joint. 
     SUMMARY 
     The foregoing and other features and advantages of the invention will be apparent to those of ordinary skill in the art from the following more particular description of the invention and the accompanying drawings. 
     Disclosed is an embodiment of a total intervertebral disc replacement device comprising a cranial member, further comprising a cranial base body; a cranial adjustable body coupled to the cranial base body, wherein the cranial adjustable body adjusts along a cranial AP axis with respect to the cranial base body; a cranial articular surface coupled to the cranial adjustable body; a caudal member, further comprising a caudal base body; a caudal adjustable body coupled to the caudal base body, wherein the caudal adjustable body adjusts along a caudal AP axis with respect to the caudal base body and wherein the caudal AP axis is parallel to the cranial AP axis; a caudal articular surface coupled to the caudal adjustable body; and a joint comprising, the cranial articular surface and the caudal articular surface, wherein the caudal articular surface moveably engages with the cranial articular surface. 
     In some embodiments, the cranial adjustable body is slidably coupled to the cranial base body and the caudal adjustable body is slidably coupled to the caudal base body 
     In some embodiments, the total intervertebral disc replacement device further comprises an attachment apparatus, wherein the cranial base body is coupled to a cranial vertebral body and the caudal base body is coupled to a caudal vertebral body by the attachment apparatus. In some embodiments, the attachment apparatus comprises a biocompatible adhesive coupled to a cranial adhesive surface of the cranial base body and to a caudal adhesive surface of the caudal base body. In some embodiments, the attachment apparatus comprises a cranial screw strut; a cranial bone screw; a caudal screw strut; and a caudal bone screw. 
     In some embodiments, the cranial articular surface comprises a concave curvature and the caudal articular surface comprises a convex curvature, wherein the convex curvature corresponds to the concave curvature. 
     In some embodiments, the total intervertebral disc replacement device further comprises a first cranial actuator coupled to the cranial base body and engaging the cranial adjustable body; and a first caudal actuator coupled to the caudal base body and engaging the caudal adjustable body. In some embodiments, the first cranial actuator limits motion of the cranial adjustable body relative to the cranial base body along the cranial AP axis, and the first caudal actuator limits motion of the caudal adjustable body relative to the caudal base body along the caudal AP axis. In some embodiments, the first cranial actuator adjusts the position of the cranial adjustable body relative to the cranial base body along the cranial AP axis, and the first caudal actuator adjusts the position of the caudal adjustable body relative to the caudal base body along the caudal AP axis. In some embodiments, further comprises a unitary actuator coupled to the cranial base body or the caudal base body, and engaging the cranial adjustable body or the caudal adjustable body, wherein activation of the unitary actuator positions the joint relative the cranial base body and the caudal base body. 
     In some embodiments, the total intervertebral disc replacement device further comprises a first cranial track wherein a long axis of the cranial track is parallel to the cranial AP axis; a first cranial biasing member engaging the cranial adjustable body, wherein the first cranial biasing member biases motion of the cranial adjustable body in a direction along the cranial AP axis relative to the cranial base body; a first caudal track wherein a long axis of the caudal track is parallel to the caudal AP axis; and a first caudal biasing member engaging the caudal adjustable body, wherein the first caudal biasing member biases motion of the caudal adjustable body in a direction along the caudal AP axis relative to the caudal base body. 
     Disclosed is a total intervertebral disc replacement device comprising a cranial member, further comprising a cranial base body; a cranial adjustable body slidably coupled to the cranial base body, wherein the cranial adjustable body slides within a cranial plane with respect to the cranial base body; a cranial articular surface coupled to the cranial adjustable body; a caudal member, further comprising a caudal base body; a caudal adjustable body slideably coupled to the caudal base body, wherein the caudal adjustable body slides within a caudal plane with respect to the caudal base body and wherein the caudal plane is parallel to the cranial plane; and a caudal articular surface coupled to the caudal adjustable body, wherein the caudal articular surface moveably engages with the cranial articular surface. 
     In some embodiments, the total intervertebral disc replacement device further comprises a first cranial actuator coupled to the cranial base body and engaging the cranial adjustable body, wherein the first cranial actuator limits sliding motion of the cranial adjustable body with respect to the cranial base body along a cranial AP axis; a second cranial actuator coupled to the cranial base body and engaging the cranial adjustable body, wherein the second cranial actuator limits sliding motion of the cranial adjustable body with respect to the cranial base body along a cranial lateral axis; a first caudal actuator coupled to the caudal base body and engaging the caudal adjustable body, wherein activation of the first caudal actuator limits sliding motion of the caudal adjustable body with respect to the caudal base body along a caudal AP axis; and a second caudal actuator coupled to the caudal base body and engaging the caudal adjustable body, wherein the second caudal actuator limits sliding motion of the caudal adjustable body with respect to the caudal base body along a caudal lateral axis. 
     In some embodiments, the total intervertebral disc replacement device further comprises an AP movement mechanism comprising a first cranial track wherein a long axis of the cranial track is parallel to the cranial AP axis; a first cranial biasing member engaging the cranial adjustable body, wherein the cranial biasing member biases motion of the cranial adjustable body in a direction along the cranial AP axis relative to the cranial base body; a first caudal track wherein a long axis of the caudal track is parallel to the caudal AP axis; and a first caudal biasing member engaging the caudal adjustable body, wherein the first caudal biasing member biases motion of the caudal adjustable body in a direction along the caudal AP axis relative to the caudal base body; and a lateral movement mechanism comprising a second cranial track wherein a long axis of the second cranial track is parallel to a cranial lateral axis; a second cranial biasing member engaging the cranial adjustable body, wherein the second cranial biasing member biases motion of the cranial adjustable body in a direction along the cranial lateral axis relative to the cranial base body; and a second caudal track wherein a long axis of the second caudal track is parallel to a caudal lateral axis; and a second caudal biasing member engaging the caudal adjustable body, wherein the second caudal biasing member biases motion of the caudal adjustable body in a direction along the caudal lateral axis relative to the caudal base body. 
     Disclosed is a method of surgically implanting a total intervertebral disc replacement device, comprising the steps of excising an intervertebral disc joint; coupling an intervertebral total disc replacement device to a vertebral body; and articulating a cranial articular surface with a caudal articular surface of a total intervertebral disc replacement device. 
     In some embodiments, the method further comprises a step radiographing the position of the total intervertebral disc replacement device. In some embodiments, the method further comprises a step intraoperatively fluoroscoping the position of the total intervertebral disc replacement device. In some embodiments, the method further comprises a step adjusting the position of an articular surface of the coupled total intervertebral disc replacement device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1(A)  is a perspective view of a total intervertebral disc replacement device; 
         FIG. 1(B)  is a perspective view of a cranial member and a caudal member of a total intervertebral disc replacement device; 
         FIG. 1(C)  is a perspective view of a total intervertebral disc replacement device implanted in a cervical spine, with a cranial articular surface and a caudal articular surface partially separated; 
         FIG. 1(D)  is a front view of a total intervertebral disc replacement device implanted in a cervical spine, with cranial articular surface  129  contacting caudal articular surface  149 ; 
         FIG. 2  is a left side view of a total intervertebral disc replacement device; 
         FIG. 3  is a right side view of a total intervertebral disc replacement device; 
         FIG. 4  is a front (anterior) view of a total intervertebral disc replacement device, 
         FIG. 5  is a back (posterior) view of a total intervertebral disc replacement device; 
         FIG. 6  is a top view of a total intervertebral disc replacement device, 
         FIG. 7  is a bottom view of a total intervertebral disc replacement device; 
         FIG. 8  is an exploded perspective view of a caudal member of a total intervertebral disc replacement device, 
         FIG. 9  is a bottom exploded view of a cranial member of a total intervertebral disc replacement device; 
         FIG. 10  is an exploded perspective view of a caudal member of a total intervertebral disc replacement device; 
         FIG. 11  is a flowchart of a method of inserting a total intervertebral disc replacement device in a patient; 
         FIG. 12  is a flowchart of an alternative embodiment of a method of inserting a total intervertebral disc replacement device in a patient; 
         FIG. 13  is a flowchart of an additional alternative embodiment of a method of inserting a total intervertebral disc replacement device in a patient; and 
         FIG. 14  is a flowchart of an additional alternative embodiment of a method of inserting a total intervertebral disc replacement device in a patient. 
     
    
    
     DETAILED DESCRIPTION 
     As discussed above, the disclosed invention relates to artificial IVD joints. In particular, the invention relates to artificial implantable IVD joints with a “floating” COR, including artificial IVD joints with controls for adjusting the COR position. 
     Total disc replacement (“TDR”) devices are available for treatment of patients with a wide variety of severe inflammatory and degenerative conditions of the cervical IVD, including but not limited to spondylolisthesis, degenerative disc disease, spinal cord nerve compression, and trauma. Motion-preserving TDR procedures for cervical IVD are available for patients. The spine surgeon may choose and favor a TDR implant device based on the patient&#39;s anticipated postoperative activity level and to minimize adjacent segment disease (“ASD”). Commonly employed TDR implant devices use a ball-and-socket or similar design with a fixed COR and rotation-coupled translation. With constrained motion about a fixed COR, the positioning of the TDR implant device intraoperatively may, therefore, affect resulting postoperative kinematics. 
     In vivo, the intervertebral axis of rotation is affected by physiologic conditions. With reference to mechanics, the instantaneous COR of a rigid plane moving within a plane is a centrode. Fixed-position TDR devices are typically implanted intraoperatively by centering the TDR endplates in the midline of the vertebral bodies, creating a fixed COR. The patient&#39;s natural COR, however, is not fixed, but changes with spinal motion. The axis of rotation of two vertebral bodies separated by an IVD is dynamic, describing a centrode. This dynamic axis of rotation, however, is not duplicated by currently available TDR devices. In current TDR devices, the axis of rotation is fixed and translation is allowed only when coupled with rotation. 
     Ideally, vertebral endplate positioning of a TDR device should not necessarily be centered over the COR of the vertebral bodies, which is not fixed, but rather be determined based upon the biomechanical consequences of anterior-posterior (“A/P”) and lateral variations of the vertebral endplate positioning of the TDR device. The biomechanics may be defined and consequences of various TDR endplate positions predicted by measuring changes in facet loading and the instantaneous axis of rotation (“IAR”) with flexion and extension, lateral bending, and rotation at various levels following TDR. One way to obtain these measurements is by performing TDR in fresh human cadaver spines and then taking the measurements directly in various states of A/P flexion/extension, lateral bending, and axial rotation. 
     Because of the fixed nature of currently available TDR devices, the endplate placement position on the vertebral body affects the IAR, the overall range of motion (“ROM”), the facet joint load distribution, and vertebral coupling—combination of lateral bending with axial rotation depending upon the anatomic characteristics of the intervertebral and facet joints at a given level of the spine. To replicate the moving non-fixed nature of the COR in the centrode, a biasing member may be used, a non-limiting example being a spring, to control the travel of an adjustable body coupled to an articular surface. For example, a stiff spring would allow less movement of the adjustable body (small centrode envelope) compared to a relatively less-stiff spring (large centrode envelope). 
     Embodiments of the invention address this and other limitations by providing a TDR device which allows for adjusting the COR by partially replicating the natural “floating” COR. A total IVD replacement device may be adjusted based upon force distribution across the intervertebral and facet joint surfaces during rotation and IAR characteristics with flexion/extension, lateral bending, and axial rotation. Adjustable positioning allows the spine surgeon to optimize load distribution and stability, providing optimal performance based upon the physical parameters, age, and activity requirements of the individual patient. Embodiments of the invention selectively position prosthetic IVD joint articular surfaces between opposing vertebral end plates to account for the non-fixed nature of the COR, or centrode, of the natural IVD joint. 
       FIG. 1(A)  shows an total IVD replacement total IVD replacement device  100 . Total IVD replacement device  100 , in some embodiments, is surgically implanted in the operating room under general anesthesia to replace a diseased or damaged IVD.  FIG. 1(C)  and  FIG. 1(D)  show a front perspective and front view respectively of an example embodiment of total IVD replacement device  100  implanted between the fifth cervical vertebra and the sixth cervical vertebra of a human cervical spine. The various embodiments of total IVD replacement device  100  may be sized and otherwise configured appropriately for implantation at cervical spinal levels in some embodiments, at thoracic spinal levels in some embodiments, and at lumbar spinal levels in some embodiment. In some embodiments, implantation requires substantial removal of the IVD, including some or all of the annulus and some or all of the nucleus pulposis. In some embodiments, a portion of the vertebral body above and below the disc space is also removed as necessary to create a space for insertion of total IVD replacement device  100  without substantially altering the length of and/or transmitting a compressing or distracting force to other levels of the spinal column. This may be somewhat appreciated by the embodiment shown in  FIG. 1(D) . An anterior surgical approach for implantation of total IVD replacement device  100  is preferable, in some embodiments. In some embodiments, a lateral surgical approach may be used to expose the adjoining vertebral bodies for IVD replacement. In some embodiments, still other surgical approaches may be used. 
     As shown in the embodiment illustrated in  FIG. 1(A)  and  FIG. 1(B) , total IVD replacement device  100  comprises two primary components: a cranial member  120  and a caudal member  140 . Cranial member  120  and caudal member  140  are each an assembly of components (see exploded views in  FIG. 8 - FIG. 10 .) In the example embodiment shown in the drawing figures, and in some other embodiments, cranial member  120  and caudal member  140  are the same, wherein caudal member  140  is merely an upside-down cranial member  120 . In no way, however, is this intended to be limiting. Some embodiments of the invention employ, for example, different shapes, articular surfaces, actuator means, adjustable body-base body coupling means, and other aspects distinguishing cranial member  120  and caudal member  140  from one another. 
     Cranial member  120  and caudal member  140  each, in some embodiments, comprise a base body and an adjustable body coupled to an articular surface, wherein the adjustable body is moveable in relation to the base body. In some embodiments, the adjustable body is moveable along an anteroposterior axis AP, as shown in  FIG. 1(A) . In some embodiments, the adjustable body is movable along a lateral axis L, as shown in  FIG. 1(A) . In some embodiments, the adjustable body is movable along both anteroposterior axis AP and lateral axis L. In some embodiments, the adjustable body position is controlled by a biasing member acting along anteroposterior axis AP. In some embodiments, the adjustable body is controlled by a biasing member acting along lateral axis L. In some embodiments, the adjustable body is positioned by an actuator, wherein a spine surgeon or other healthcare provider may adjust the position of the adjustable body with respect to its respective base body. These example embodiments are discussed in detail herein below. 
       FIG. 1  also shows a cranial base body  122  that, when implanted in a patient, attaches to the caudal aspect of the vertebral body immediately cranial to the IVD replacement level. For example, in an IVD replacement at C5-C6, cranial base body  122  attaches to the caudal aspect of the fifth cervical vertebral body. Also in this example, and as suggested by  FIG. 1(D) , a caudal base body  142  attaches to the cranial aspect of the sixth cervical vertebral body. 
     Cranial base body  122 , caudal base body  124 , and other components of total IVD replacement device  100  are constructed from non-toxic, biocompatible substances, such as those known in the art and currently used in other prosthetic devices. Examples include polyethylene for articular surfaces. Cobalt-chromium alloys, titanium, titanium allows, tantalum, zirconium and its alloys, and polyethylene may be used for the base bodies, adjustable bodies, and other components of total IVD replacement device  100 . There materials are listed by way of example only. Other non-toxic, corrosion-resistant, biocompatible materials are be used, in some embodiments. 
     In some embodiments, a cranial attachment apparatus  110  couples cranial base body  122  to a caudal aspect of a cranial vertebral body and a caudal attachment apparatus couples caudal base body  142  to the cranial aspect of a caudal vertebral body. In some embodiments, such as the embodiment shown in  FIG. 1(D) , cranial attachment apparatus  110  comprises a cranial screw strut  111  and a cranial bone screw  112 . Two cranial bone screws  112  engaging cranial base body  122  through a pair of cranial screw struts  111  and two caudal bone screws  162  engaging caudal base body  142  through a pair of caudal screw struts  161  are shown in the embodiment illustrated in  FIG. 1(D) . This is not meant to be limiting, other suitable mechanical attachment apparatuses can be employed. Another apparatus attaching a base body to an adjacent vertebral body is a biocompatible bone cement coupled to a cranial adhesive surface  113  or a caudal adhesive surface  163 . Examples of bone cement include, but are not limited to, synthetic self-curing compounds such as polymethyl methacrylate (“PMMA”) and methyl methacrylate (“MMA.”) The mechanical attachment apparatuses may comprise bone screw(s) biocompatible adhesive, or a combination of bone screw(s)  102  and biocompatible adhesive. Other fasteners, cements, or alternative attachment or coupling apparatuses are employed in some embodiments to maintain total IVD replacement device  100  coupled to adjacent vertebral bodies, including natural in-vivo anatomic structures and forces, in some embodiments. 
     As shown by the various exploded, views in the drawing figures referenced above and further discussed below, cranial member  120  and caudal member  140  also comprise an example of a total IVD replacement device  100  wherein the respective adjustable bodies are movably coupled to the respective base bodies, in some embodiments. Cranial member  120  and caudal member  140  each comprise an articular surface; cranial adjustable body  127  of cranial member  120  comprises a cranial articular surface  129  and caudal adjustable body  147  of caudal member  140  comprises a caudal articular surface  149 . 
     Cranial articular surface  129  and caudal articular surface  149  moveably engage one another to form an artificial joint interface of total IVD replacement device  100  and reconstruct the motion, load-bearing, and force distribution characteristics of the replaced IVD. Cranial articular surface  120  and caudal articular surface  140  are shown in  FIG. 2 - FIG. 10  as flat, planar surfaces. This is not meant to be limiting, but rather to offer a simple example for clarity. Cranial articular surface  129  and caudal articular surface  140  may be fashioned into any manner of complimentary shapes that moveably engage one-another to allow for motion across the total IVD replacement device  100 . One example of such complimentary shapes is a partial ball-and-socket configuration, as in the embodiment of total IVD replacement device  100  shown in  FIG. 1(C)  and  FIG. 1(D) . These two figures show an embodiment of total BID replacement device  100  wherein caudal articular surface  149  is a partial convexity, as shown by  FIG. 1(C) , and cranial articular surface  129  is a corresponding partial concavity (incompletely shown by the figure.) In alternative embodiments, the convexity may be on cranial articular surface  120  and the concavity on caudal articular surface  149 . Other shapes and examples are possible for cranial articular surface  120  and caudal articular surface  149 . In some embodiments, the artificial joint interface is a surface allowing only flexion-extension. 
     In the example embodiment shown in  FIG. 1(B) , caudal articular surface  149  is coupled to a caudal adjustable body  147  of caudal member  140 . In the embodiment shown in  FIG. 1(A)  and  FIG. 1(B) , caudal base body  147  comprises a second recess  157  defining an inner volume having a perimeter. Second adjustable body  147  is coupled within second recess  157  and moveable within the perimeter of second recess  157 . Caudal adjustable body  147  extends from the inner volume of second recess  157 . In some embodiments, a first caudal actuator  144  engages caudal adjustable body  147 . In some embodiments, a second caudal actuator  145  (not shown) engages caudal adjustable body  147 . In the embodiments shown, caudal adjustable body  147  moves parallel to anteroposterior line AP (shown in  FIG. 1(A) ). In some embodiments (not shown), caudal adjustable body  147  moves parallel to lateral line L, perpendicular to anteroposterior line AP. In some embodiments, caudal adjustable body  147  moves two-dimensionally in a plane wherein anteroposterior line AP and lateral line L are coplanar, defining a plane wherein the instantaneous COR of caudal adjustable body  147  is located within the plane. In some embodiments, first caudal actuator  144  engages caudal adjustable body  147  and controls movement of caudal adjustable body  147  in a direction parallel with anteroposterior line AP. In some embodiments, second caudal actuator  145  engages caudal adjustable body  147  and controls movement of caudal adjustable body  147  in a direction parallel with lateral line L. In some embodiments, caudal adjustable body  147  remains in a non-fixed position, moving in the plane defined by the coplanar lines line AP and line L. 
     In some embodiments, caudal adjustable body  147  is adjusted to a non-fixed position or partially fixed position with an instantaneous COR located on a plane defined by the A/P axis and the lateral axis. In these and some other embodiments, second actuator activates caudal adjustable body  147  so as to control motion along the A/P axis, the lateral axis, or a combination of both the A/P and the lateral axes. 
     Similar to caudal member  140 , cranial member  120 , in some embodiments, comprises a cranial adjustable body  127  comprising a cranial articular surface  129 . Cranial base body  122  comprises a first recess  137  defining an inner volume having a perimeter. Cranial adjustable body  127  is coupled within first recess  137  and moveable within the perimeter of first recess  137 . Cranial adjustable body  127  extends from the inner volume of first recess  137 . In some embodiments, a first cranial actuator  124  engages cranial adjustable body  127 . In some embodiments, first cranial actuator  124  or second cranial actuator  125  control movement of cranial adjustable body  127  in scope and manner similar to the activation and control of caudal adjustable body  147  by first caudal actuator  144  and second caudal actuator  145  of caudal member  140 , discussed above. In some embodiments, the motion of first adjustable body  127  is controlled by first cranial actuator  124  or second cranial actuator  125  in scope and manner substantially different than the control of second adjustable body  147  by first caudal actuator  144  or second caudal actuator  145 . In some embodiments, the manner of activation employed by first cranial actuator  124 , second cranial actuator  125 , first caudal actuator  144 , and second caudal actuator  145  is substantially the same. In some embodiments, first cranial actuator  124  or first caudal actuator  144  is a unitary actuator, wherein either first cranial actuator  124  or first caudal actuator  144  positions both cranial adjustable body  127  and caudal adjustable body  147  simultaneously along line AP. In some embodiments, second cranial actuator  125  or second caudal actuator  145  is a unitary actuator, wherein either second cranial actuator  125  or second caudal actuator  144  positions both cranial adjustable body  127  and caudal adjustable body  147  simultaneously along line L. 
     In some embodiments, adjustments are performed non-surgically by remotely adjusting any one or more of first cranial actuator  124 , second cranial actuator  125 , first caudal actuator  144 , or second caudal actuator  145  in any combination based upon data generated from an internal cranial stress monitoring device (not shown in the Figures), an internal caudal stress monitoring device (not shown in the Figures), or data generated from both the internal cranial stress monitoring device and the internal caudal stress monitoring device. In some embodiments, either or both the internal cranial stress monitoring device and the internal caudal stress monitoring device are coupled to IVD replacement device  100 . In some embodiments, either or both the internal cranial stress monitoring device and the internal caudal stress monitoring device are not coupled to IVD replacement device. Either or both of the internal cranial stress monitoring device and the internal caudal stress monitoring device may be mechanically coupled to an intervertebral disc, a vertebral body, an intervertebral facet joint, a vertebral lamina, a vertebral pedicle, or any other vertebral or intervertebral anatomic structure adjacent to or remote from the spinal level of total IVD replacement device  100  insertion, without limitation. This use of stress monitoring devices for internal stress monitoring, in some embodiments, directs and allows for non-surgical adjustments of cranial adjustable body  127  or caudal adjustable body  147  to be performed at any time, according to changes in force distribution along the anterior or posterior spinal columnar elements to create and maintain a favorable distribution of forces within the spinal column. 
       FIG. 2  is a left side view of total IVD replacement device  100 . As shown in  FIG. 2 , cranial member  120  contacts caudal member  140  at the interface between cranial articular surface  129  and caudal articular surface  149 . Also shown in  FIG. 2  is a cranial screw strut  123  of cranial base member  122  and a caudal screw strut  143  of caudal base member  142 . Cranial screw strut  123  and caudal screw strut  143  in the embodiment shown direct a bone screw into a vertebral body at an angle suitable to create a force component tending to secure each base member upward or downward (i.e. cranially or caudally) against its corresponding vertebral body. 
       FIG. 2  shows the small portion of cranial adjustable body  127  and caudal adjustable body  147  extending from a cranial base body  122  and caudal base body  142  respectively. In the embodiment shown in the figures, this exposed portion of each adjustable body comprises a flange which contacts a sliding surface of the corresponding base body. Cranial adjustable body  127  comprises a cranial flange  128  and second adjustable body  147  comprises a caudal flange  148 . The full shape of cranial adjustable body  127  and caudal adjustable body  147 , including cranial flange  128  and caudal flange  148 , is shown in the exploded drawing figures ( FIG. 8 - FIG. 10 ) discussed herein below. 
       FIG. 2  also shows first cranial actuator  124  and first caudal actuator  144  partially engaged within cranial base member  122  and caudal base member  142  respectively. First actuator  124  and second actuator  144  are shown fully engaged within the corresponding base members  122  and  142  by  FIG. 1(D) . In this and some other embodiments, first cranial actuator  124  and first caudal actuator  144  are bolts which are accessed from an anterior (front-side) position. This facilitates activating the corresponding adjustable body in the A/P axis. Some embodiments may employ first actuator  124 , second actuator  144 , or both accessed from a lateral position to facilitate activating the corresponding adjustable body on the lateral axis. Other actuator apparatuses may be used, such as, for example, cams, levers, cantilevered members, an apparatus comprising a solenoid, other electronic apparatus, or a hydraulic apparatus. Any suitable apparatus for causing movement of an adjustable body, controlling movement of an adjustable body, or simultaneously both causing and controlling movement of cranial adjustable body  127  or caudal adjustable body  147  within a base body  122  or a base body  142  respectively are used in some embodiments of the invention. 
       FIG. 3  is a right side view of total IVD replacement device  100 , corresponding to the left side view shown in  FIG. 2  and described above. In the embodiments shown by the figures, there is left-right symmetry. This is not meant to be limiting. in some embodiments, asymmetry between the left side and the right side of total IVD replacement device  100  may be present. Additionally,  FIG. 3  shows anteroposterior axis line AP. 
       FIG. 4  is a front (anterior) view of total IVD replacement device  100 . A corresponding view of an implanted total IVD replacement device  100  mentioned above is shown by  FIG. 1(D) . In the embodiment shown by  FIG. 4 , total IVD replacement device  100  projects backward (posteriorly) into the intervertebral space, replacing the excised IVD, at the level where total IVD replacement device  100  is implanted in the spinal column. First cranial actuator  124  and first caudal actuator  144  are shown, along with the midline positioning of each actuator in the illustrated embodiment. Also shown in  FIG. 4  are caudal screw struts  161  oriented at an angle for engaging cranial bone screws  112 . First flange  128  of cranial adjustable body  127  and second flange  148  of caudal adjustable body  147  are also shown. 
       FIG. 5  shows a back (posterior) view of total IVD replacement device  100 . In the embodiment shown in  FIG. 5 , with the exception of cranial screw struts  123  and caudal screw struts  161 , all visible surfaces of the device in the figure are contained within the intervertebral space, cranial vertebral body, and caudal vertebral body when total IVD replacement device  100  is implanted in a spinal column. Additionally,  FIG. 5  shows lateral axis line L. 
       FIG. 6  shows a top view of total IVD replacement device  100 . Cranial base body  122 , cranial screw struts  123  and first cranial actuator  124  are the only designated structures seen in this view. Of note, cranial base member  122  comprises cranial adhesive surface  113 . Cranial adhesive surface  113  and caudal adhesive surface  163  shown in  FIG. 7 , each present a broad, flat surface for contacting the caudal aspect or cranial aspect respectively of a vertebral body when implanted into the resected IVD space. In some embodiments, cranial base body  122 , caudal base body  142 , or both elements are formed from a sufficiently porous material, such as tantalum or tantalum-ceramic, for example, to enhance penetration of bone cement and/or ingrowth of bone. In some embodiments, the combination of porous material and a relatively large surface area contributes to stable and durable fixation of cranial base body  122  and caudal base body  142  to the corresponding vertebral bodies. 
       FIG. 7  shows a bottom view of total IVD replacement device  100 . As shown by  FIG. 6  and  FIG. 7 , some embodiments of total IVD replacement device  100  present a similar profile from the top or the bottom. 
     Exploded views of  FIG. 8 - FIG. 10  demonstrate elements of one non-limiting example embodiment for positioning (moving and/or fixing in position) an adjustable body of total IVD replacement device  100  wherein the components shown have been discussed with regard to  FIGS. 1-7 . The listed elements comprising caudal member  140 , or cranial member  120 , comprise a system wherein a dynamic COR is created. The joint interface between cranial articular surface  129  and caudal articular surface  149  is movable such that the natural distribution of forces during antero-posterior flexion, lateral bending, and axial rotation of the vertebral bodies along the spinal axis on either side of the implanted total IVD replacement device  100  is preserved. 
     Different embodiments of total IVD replacement device  100  create a dynamic COR in slightly different ways, according to the movement characteristics and forces present at the IVD joint replacement level in the spinal column. For example, in some embodiments, the position of caudal adjustable body  147  relative to caudal base body  142  adjusts by moving along a first caudal track  150  in the caudal axis AP. In some embodiments, the position of caudal adjustable body  147  relative to caudal base body  142  additionally adjusts by moving along a second caudal track in the caudal axis L, wherein caudal adjustable body  147  “floats” in a plane formed by the two coplanar lines caudal axis AP and caudal axis L. First caudal track  150  may be any track, such as a pin-track as shown in  FIG. 7  and  FIG. 8 . Alternatively, first caudal track may be a groove in caudal base body  142  that engages with a shape corresponding to a tongue on caudal adjustable body  147 . In some embodiments, the groove is located on caudal adjustable body  147  and the shape comprises caudal base body  142 . In some embodiments, other pin-and-groove track mechanisms are used. 
     A similar arrangement of elements comprises cranial member  120 , such cranial adjustable body  127  moves in relation to cranial base body  122  causing the position of cranial articular surface  129  of cranial adjustable body  127  to correspond with caudal articular surface  140  of caudal adjustable body  147 . In some embodiments, cranial member  120  comprises a first cranial actuator  124  that adjusts a position of cranial adjustable body  127  along cranial axis AP by controlling movement along cranial axis AP or fixing the position of cranial adjustable body  127  along cranial axis AP. In some embodiments, cranial member  120  comprises a second cranial actuator  125  that adjusts a position of cranial adjustable body  127  along cranial axis L by controlling movement along cranial axis L or fixing the position of cranial adjustable body  127  along cranial axis L. In some embodiments, a first cranial biasing member  131  biases cranial adjustable body  127  against first cranial actuator  124 . First cranial biasing member  131  may be a compression spring, in some embodiments. In some embodiments, first cranial biasing member  131 may be a mechanical biasing member other than a compression spring. In some embodiments, first cranial biasing member  131  may be a solenoid or similar electrically-activated magnetic biasing device. 
     In some embodiments, a first caudal actuator  144  controls movement of caudal adjustable body  147  in one direction along caudal axis AP. In some embodiments, first caudal actuator  144  fixes caudal adjustable body  147  in a fixed position, wherein adjustment of first caudal actuator  144  determines the position of fixation of caudal adjustable body  147  along caudal axis AP. In some embodiments, a first caudal biasing member  151  biases caudal adjustable body  147  against first caudal actuator  144 . First caudal biasing member  151  may be a compression spring, in some embodiments and in the embodiment shown in  FIG. 8  and  FIG. 9 . In some embodiments, first caudal biasing member  151 may be a mechanical biasing member other than a compression spring. In some embodiments, first caudal biasing member  151  may be a solenoid or similar electrically-activated magnetic biasing device. 
     Such elements may comprise caudal member  140 , cranial member  120 , both, or neither in embodiments of the invention. In some embodiments, a positioning/fixing, apparatus other than shown in the drawing figures may be used. Different or similar elements may comprise caudal member  140  and cranial member  120  in some embodiment of the invention. In some embodiments, adjustment of any one actuator, such as first cranial actuator  124 , second cranial actuator  125 , first caudal actuator  144 , or second caudal actuator  145  simultaneously and correspondingly adjusts, limits, or fixes the position of both cranial articular surface  129  of cranial adjustable body  127  and caudal articular surface  149  of caudal adjustable body  147 . In some embodiments, adjustment of any two actuators correspondingly adjusts, limits, or fixes the position of both cranial articular surface  129  of cranial adjustable body  127  and caudal articular surface  149  of caudal adjustable body  147 . 
     In the embodiment shown in  FIG. 8 , and some other embodiments, caudal adjustable body  147  comprises a caudal rib  153  coupled to caudal flange  148  opposite caudal articular surface  149 . When assembled, caudal rib  153  is enveloped within caudal base body  142 . Caudal flange  128  engages a caudal sliding surface  141  of caudal base body  142 ; correspondingly, cranial flange  128  engages a cranial sliding surface  134  of cranial base body  122 . In the embodiments shown in  FIG. 8  and other drawing figures, caudal rib  153  comprises a caudal track guide  152 . In some embodiments, two caudal track guides  152  each engage a corresponding caudal track  150 . Caudal track  150  is coupled to caudal base body  142 . In some embodiments, a first cranial track  130  is similarly coupled to cranial base body  142 . in the embodiment shown in  FIG. 8 , first caudal biasing member  151  also engages first caudal track  150 , although this is not meant to be limiting. When assembled, first caudal track  150  and first caudal biasing member  151  are located within an inner volume of caudal base body  141  such that first caudal biasing member  151  is constrained and partially compressed between first caudal blocking surface  154  and second rib  153 . A similar mechanism for cranial member  120  comprising a first cranial track  130 , a first cranial biasing member  131 , cranial base body  122 , a first cranial blocking surface  134 , and a first cranial rib  133 . First cranial actuator  124  or first caudal actuator  144  engage cranial rib  133  or caudal rib  153  opposite first cranial biasing member  131  or first caudal biasing member  151  respectively such that first cranial actuator  124  or first caudal actuator  144  and first cranial actuator  131  or first caudal actuator  151  exert opposing forces against cranial rib  133  or caudal rib  153  respectively. These opposing forces operate to stabilize cranial adjustable body  127  or caudal adjustable body  147  in a position governed by the position of first cranial actuator  124  or first caudal actuator  144  respectively. The foregoing example of an apparatus for positioning an adjustable body of total IVD replacement device  100  is not meant to be limiting. Any similar or alternative but suitable means for adjusting the position of cranial articular surface  129  or caudal articular surface  149  relative to cranial base body  122  or caudal base body  142  respectively of total IVD replacement device  100  can be used. 
       FIG. 9  is a bottom (caudal) view of elements of a disassembled cranial member of a total IVD replacement device.  FIG. 9  shows cranial base body  122  and cranial adjustable body  127 , two first cranial tracks  130 , first cranial biasing member  131  and first cranial actuator  124 , in a non-limiting example embodiment. 
       FIG. 10  is an additional exploded perspective view of a caudal member of a total IVD replacement device. Similar to  FIG. 8  discussed in detail herein above,  FIG. 10  shows elements comprising caudal member  140 , including first caudal track  150  and first caudal track guide  152 , wherein caudal adjustable body  147  moves along caudal axis AP (not shown). First caudal biasing member  151  is not shown in this figure. 
       FIG. 11  is a flowchart diagram of a method  200  of surgically inserting an total IVD replacement device into a patient. Method  200  comprises an excising step  210 , a coupling step  220 , and an articulating step  230 . Excising step  210  comprises surgically removing the IVD from an intervertebral space, using established surgical techniques known in the art. In some embodiments, excising step additionally comprises excising a portion of each vertebral body bounding the excises IVD intervertebral space cranially and caudally to increase the space available for insertion of the total IVD replacement device. 
     Coupling step  220  comprises coupling a total IVD replacement device to a vertebral body. In some embodiments, coupling step comprises utilizing a commercially available bone screw designed for fixing a hardware device to a vertebral body to fix a cranial base body or a caudal base body of the total IVD replacement device to the corresponding vertebral body. In some embodiments, coupling step  220  comprises the use of a biocompatible adhesive bone cement, such as polymethyl-methacrylate, or the like. In some embodiments, coupling step  220  comprises both the use of a bone screw and an adhesive. In some embodiments, coupling step  220  comprises the use of an alternative orthopedic fixation device other than a bone screw. 
     Articulating step  220  of method  200  comprises articulating a cranial articular surface and a caudal articular surface of a total IVD replacement device. In some embodiments, articulating step  220  is performed prior to coupling step  220 . In some embodiments, articulating step  220  is performed following coupling step  220 , with or without execution of additional intervening steps, in some embodiments. 
       FIG. 12  is a flowchart diagram an alternative embodiment of method  200 .  FIG. 12  shows an additional radiographing step  240 . Radiographing step  240  comprises radiographing the position of the total IVD replacement device following coupling step  220  and articulation step  230 . Radiographing step  240  is performed utilizing established techniques known in the art and is useful to confirm proper positioning of total IVD replacement device  100  in the patient, prior to completing the surgical procedure. 
       FIG. 13  is a flowchart diagram of an additional alternative embodiment of method  200 .  FIG. 13  shows an additional fluoroscoping step  250 . Fluoroscoping step  250  comprises dynamically intraoperatively fluoroscoping the position of the total IVD replacement device. The use of intraoperative fluoroscopy is important, in some embodiments, to evaluate how the position of coupled total IVD replacement device  100  affects movement of intervertebral joints through the spinal column above and below inserted total IVD replacement device  100 . Evidence of asynchronous motion, asymmetrical motion, and unbalanced force distribution caused by an sub-optimally positioned or maladjusted total IVD replacement device is visible upon fluoroscopic evaluation during flexion-extension, lateral bending, and axial rotation, in some embodiments. The surgeon is then able to discover sub-optimal positioning or adjustment of the total IVD replacement device and attempt to correct the position or adjustment while the patient remains under anesthesia in the operating room. 
       FIG. 14  is a flowchart diagram yet another alternative embodiment of method  200 .  FIG. 14  shows an additional adjusting step  260 . Adjusting step  260  comprises adjusting the position of an articular surface of the coupled total IVD replacement device. In some embodiments, adjusting step  260  comprises adjustment of an actuator to adjust, move, or fix the position of the articular surface. In some embodiments, adjusting step  260  is performed following radiographing step  240  or fluoroscoping step  250 . In some embodiments, adjusting step  260  and fluoroscoping step  215  are alternatively and repeatedly performed until the position of the articular surface is optimized by the operating surgeon. 
     In some embodiments, adjusting step  260  is performed at a time after the patient leaves the operating room. In some embodiments, adjusting step  260  is performed by a healthcare provider other than the operating surgeon, in a remote place and at a remote time from the surgical procedure performed in a hospital to insert total IVD replacement device  100  in the patient. For example, in some embodiments, adjustments are performed non-surgically by remotely adjusting any one or more of first cranial actuator  124 , second cranial actuator  125 , first caudal actuator  144 , or second caudal actuator  145  in any combination based upon data generated from an internal cranial stress monitoring device (not shown in the Figures), an internal caudal stress monitoring device (not shown in the figures), or date generated from both the internal cranial stress monitoring device and the internal caudal stress monitoring device. 
     EXPERIMENTAL EXAMPLE AND RESULTS 
     In the course of developing various embodiments of the invention, experiments were undertaken to determine the biomechanical effects of cervical fixed-COR TDR device position variations on inter-vertebral body motion and vertebral load sharing. To develop and test a working prototype of some embodiments of the invention, an experimental model was used. In this model, TDR was performed in fresh cadaveric human donor spines at the C5-C6 position. A commercially available 5 mm M TDR device coupled to an embodiment of the invention was implanted. Implantation required a full C5-C6 disc In this and other embodiments, the A/P endplate position is adjustably controlled with a center set screw, wherein two full screw rotations translates the endplate position by 1 mm in the A/P plane. 
     In one experimental example, fresh, un-embalmed cadaver spine specimens comprising integrated segments C3-T1 from five human donors (three male and two female, mean age±standard deviation of 49.2±11.2 years) were used. Stain gauges were attached to the right and left lamina of C5 to monitor vertebral load sharing across the C5/C6 facet joints immediately above the TDR index level (C5-C6). The specimens were tested quasi-statically using pure moments (1.5 Newton-meters) in flexion-extension (“FE”), right and left axial rotation (“AR”), and right and left lateral bending (“LB”) in the following confmurations: 1) normal/intact (no TDR); 2) centered TDR; 3) TDR positioned 2 millimeters (“MM”) anteriorly; and 4) TDR positioned 2 mm posteriorly, The testing order in configurations 2, 3, and 4 above was randomized among the specimens. Anteroposterior (“A/P”) device positions were controlled on custom designed and fabricated inferior and superior implant base plates with implant positions verified using X-ray fluoroscopic A/P and lateral views. Collected data included range of motion (“ROM”), lax zone/stiff zone, location of COR, angular coupling, and changes in surface strain indicating changes in load sharing across the anterior (vertebral bodies/IVD joints) and posterior (facet joints) elements of the vertebral column. The effects of TDR position variations were analyzed by comparing the changes from normal and using RM-ANOVA with a p-value of 0.05. 
     Results showed that the A/P TDR position variations had a greater effect on the ROM during FE than during LB and AR, however the changes were not statistically significant in any direction of motion. The effects of TDR position variations on coupled motion, including AR during LB and LB during AR, were not significant. The axis of rotation shifted in the direction of the changed TDR position. 
     There were, however, notable changes in laminar strains, indicating changes in facet loads within the posterior column. These results were interpreted to show that although A/P position variations of greater than 2 mm of a cervical TDR at the C5-C6 level have a fixed COR not significantly affected by the ROM or coupled motion, IAR and laminar strains show significant load-sharing changes between the anterior and posterior spinal columns via the facet joints. 
     An total IVD replacement device has been described. Preliminary testing of a prototype of some embodiments of the invention suggests the total IVD replacement device performs well in the experimental model and provides superior versatility compared to TDR devices currently available and described in the art. The total IVD replacement device is surgically implanted to replace an IVD damaged by disease, trauma, or other degenerative process. Elements of the invention enable adjustment of the relative positions of the joint&#39;s articular surfaces, allowing for optimization of load distribution between the anterior and posterior spinal elements, thus increasing stability and providing optimal performance specific to the age, physical parameters, and activity requirements of an individual patient. 
     The embodiments and examples set forth herein were presented in order to best explain the present invention and its practical application and to thereby enable those of ordinary skill in the art to make and use the invention. However, those of ordinary skill in the art will recognize that the foregoing description and examples have been presented for the purposes of illustration and example only. The description as set forth is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the teachings above without departing from the spirit and scope of the forthcoming claims.