Abstract:
A dynamic spine prosthesis (such as a facet joint prosthesis having an articulation surface configured to articulate with a corresponding facet joint element) that has a fixation element with an elongated bone entry portion defining a longitudinal axis and a dynamic spine prosthesis component connected to the fixation element at a connection location by an adjustable connection. The adjustable connection has first and second washers each rotatably supported by the fixation element and each having an angled contact surface in a plane not perpendicular to the longitudinal axis of the fixation element, with the connection location being between the bone entry portion and the first and second washers.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit under 35 U.S.C. § 119 of U.S. Provisional Application No. 60/837,458 filed Aug. 11, 2006, which application is incorporated by reference as if fully set forth herein. 
    
    
     INCORPORATION BY REFERENCE 
     All publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     The invention relates generally to dynamic spine prostheses. In particular, the invention relates to dynamic spine prostheses with components whose position with respect to a spine fixation element may be adjusted. 
     There are multiple types of spine modification devices that may be implanted by attachment to one or more vertebrae to treat a variety of disorders. For example, spinal fusion systems fix the spatial relationships between two or more vertebrae. One such system is described in U.S. Pat. No. 6,080,156. Fusion systems, such as the one shown in the &#39;156 patent, are typically attached to the vertebrae by screws placed in the pedicle. Because all components of such fusion systems are essentially immobile with respect to each other, each component must continually bear and transmit to adjacent components all forces exerted on the device anywhere in the device until the treated vertebral bodies have fused, at which point the bony fusion generally absorbs the majority of the intervertebral loads. Because such fusion devices are typically utilized in conjunction with other fusion-promoting techniques and tools, such as disc evacuation and packing with bone graft, the use of interbody fusion cages and bone graft, gutter grafting and/or the use of BMP or other arthrodesis promoting tools and techniques, it is generally only necessary for such fusion devices to function for a limited amount of time before the arthrodesis assumes the majority of the vertebral loading. 
     Unlike fusion systems, however, dynamic spine prostheses attach to two or more vertebrae and have components that move with respect to each other as the vertebrae to which they are attached move. Moreover, dynamic spine prostheses should be designed to assume normal physiological loading (as well as transient excessive loading conditions) for the lifetime of the patient, which could easily exceed 10,000,000 cycles or more. Dynamic spine prostheses can include artificial facet joint prostheses (such as, e.g., the Total Facet Arthroplasty System® available from Archus Orthopedics, Inc., the AFRS system available from Facet Solutions, and the TOPS system available from Impliant, Ltd.) as well as dynamic stabilization systems (such as, e.g., the Stabilimax NZ system available from Applied Spine Technologies, the Axient system available from Innovative Spinal Technologies, the N-Flex system available from N-Spine, and the Accuflex system available from Globus Medical.) and dynamic interspinous-spacer systems (such as, e.g., the X-Stop system available from Kyphon/St. Francis Medical Technologies, the Coflex system available from Paradigm Spine, the Extensure system available from Nuvasive, and the Wallis system available from Abbott Spine.). 
     SUMMARY OF THE INVENTION 
     Due to patient to patient differences in spinal anatomy as well as to anatomical changes caused by a particular patient&#39;s disease state, the relationship between the fixation elements (such as screws, posts, etc.) of a dynamic spine prosthesis to the remaining components of the prosthesis may vary from patient to patient and from disease state to disease state. However, unlike spinal fusion prosthesis, the connections between the fixation elements and the dynamic (or motion-allowing) elements of a dynamic spine prosthesis must be capable of withstanding repetitive loading (both normal physiological loading as well as transient excessive loading) for the remaining lifetime of the patient. The invention therefore provides an adjustable connection between a dynamic spine prosthesis fixation element and other components of the prosthesis which is capable of withstanding such loading for an extended period of time, up to, and including, the lifetime of the patient and/or the implant. Moreover, because physicians will also often desire the fixation elements to be placed in a desired location and/or orientation relative to the surrounding anatomical structures (such as to increase the strength of the of the fixation by maximizing cortical bone purchase and/or to accommodate unusual or size-constrained anatomical features), and such positioning is often non-optimal for the placement of the dynamic elements of the device, the present invention allows the physician to place the fixation elements in virtually any orientation or position, and then securely fix the properly-functioning implant relative to the location and/or orientation of the fixation members. 
     The invention relates generally to implantable devices, apparatus or mechanisms that are suitable for implantation within a human body to restore, augment, and/or replace hard tissue, soft tissue and/or connective tissue, including bone and cartilage, and systems for treating the anatomic or functional manifestation of injury or diseases, such as spinal pathologies. In some instances, the implantable devices can include devices designed to replace missing, removed, or resected body parts or structure. The implantable devices, apparatus or mechanisms are configured such that the devices can be formed from parts, elements or components which alone or in combination comprise the device. The implantable devices can also be configured such that one or more elements or components are formed integrally to achieve a desired physiological, operational or functional result such that the components complete the device. Functional results can include the surgical restoration and functional power of a joint, controlling, limiting or altering the functional power of a joint, and/or eliminating the functional power of a joint by preventing joint motion. Portions of the device can be configured to replace or augment existing anatomy and/or implanted devices, and/or be used in combination with resection or removal of existing anatomical structure. 
     One aspect of the invention provides a dynamic spine prosthesis (such as, for example, a facet joint prosthesis having an articulation surface configured to articulate with a corresponding facet joint element) that has a fixation element with an elongated bone entry portion defining a longitudinal axis and a dynamic spine prosthesis component connected to the fixation element at a connection location by an adjustable connection. The adjustable connection has first and second washers each rotatably supported by the fixation element and each having an angled contact surface in a plane not perpendicular to the longitudinal axis of the fixation element, with the connection location being between the bone entry portion and the first and second washers. 
     In some embodiments, the angled contact surfaces of the first and second washers are in contact with each other. There also may be a third washer between the dynamic spine prosthesis connection location and the bone entry portion, with the third washer comprising a partial spherical surface. 
     In some embodiments, the dynamic spine prosthesis also has a tightening element (such as, e.g., a compression nut) having a first position enabling movement between the first and second washers and the fixation element and a second position preventing movement between the washers and the fixation element. 
     In some embodiments, the adjustable connection also has a structural attachment element supporting the dynamic spine prosthesis component, with the structural attachment element having a first position in which the dynamic spine prosthesis component is movable with respect to the structural element and a second position in which the dynamic spine prosthesis component is fixed with respect to the structural element. 
     Another aspect of the invention provides a method of adjusting a position of a component of a dynamic spine prosthesis (such as a facet joint prosthesis having an articulation surface configured to articulate with a corresponding facet joint element) with respect to a bone fixation element supporting the dynamic spine prosthesis. The method includes the steps of inserting a bone entry portion of the fixation element into a vertebra; moving the dynamic spine prosthesis component to a desired position with respect to a connection location between the dynamic spine prosthesis component and the fixation element, the connection location being between the bone entry portion and first and second washers, the first and second washers each having an angled contact surface in a plane not perpendicular to a longitudinal axis of the fixation element and being supported by the fixation element; rotating the first washer with respect to the second washer; and immobilizing the washers and the dynamic spine prosthesis component with respect to the fixation element. 
     In some embodiments, the method includes the step of rotating the second washer with respect to the fixation element. 
     In some embodiments, the step of moving the dynamic spine prosthesis component includes the step of moving the dynamic spine prosthesis component with respect to a support disposed at the connection location. In some embodiments, the immobilizing step may include the step of immobilizing the dynamic spine prosthesis component with respect to the support, such as by tightening a compression nut threadably mounted on an extension of the fixation element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features of the invention are set forth with particularity in the claims that follow. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which. 
         FIG. 1  is front elevational view of a dynamic spine prosthesis according to one embodiment of the invention. 
         FIG. 2  is a perspective view of the dynamic spine prosthesis of  FIG. 1 . 
         FIG. 3  is a right side elevational view of the dynamic spine prosthesis of  FIG. 1 . 
         FIG. 4  is a left side elevational view of the dynamic spine prosthesis of  FIG. 1 . 
         FIG. 5  is a bottom elevational view of the dynamic spine prosthesis of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1-5  show one embodiment of a dynamic spine prosthesis according to this invention. In this embodiment, the dynamic spine prosthesis is an artificial facet joint prosthesis  100  providing left and right cephalad facet joint bearing elements  102  and  104  and left and right caudal facet joint bearing elements  106  and  108 , respectively. When the cephalad facet joint bearing elements are attached to a superior vertebra and the caudal facet joint bearing elements are attached to an inferior vertebra, the corresponding left and right bearing elements move with respect to each other and bear against each other as the patient moves his or her back, which is often a combination of one of more of the following motions: flexion, extension, rotation and/or lateral bending. 
     The cephalad facet joint bearing elements attach to a superior vertebra via fixation elements, such as screws  110  and  112  having threaded bone entry portions. A left arm  114  extends generally downward from fixation element  110  to a support bar  116  to which left cephalad bearing element  102  is attached. Likewise, a right arm  118  extends generally downward from fixation element  112  to a support bar  120  to which right cephalad bearing element  104  is attached. A crossbar  122  extends between the right and left cephalad bearing elements. 
     Because of differences in patient anatomy, the cephalad portion of the dynamic spine prosthesis has adjustment mechanisms for adjusting the spatial relationship between the fixation elements and the other prosthesis components. First, the angle between the left cephalad fixation element  110  and the left support arm  114  may be adjusted and fixed in the adjusted position by rotating two angled washers  124  and  126  mounted on a proximal extension of fixation element  110  between the proximal face  127  of a fixation region  128  on the top end of arm  114  and a compression nut  130  or other tightening element. Because each washer  124  and  126  has a contact surface not perpendicular to the axis of fixation element  110 , each washer  124  and  126  may be rotated about fixation element  110  to change the angle between arm  114  (and, therefore, cephalad bearing element  102 ) and fixation element  110 . When the proper orientation has been set, tightening element  130  is tightened along a threaded proximal extension of fixation element  110  to keep the components in place. 
     In this embodiment, a partially spherical washer  132  is disposed between the distal face  129  of the left cephalad support arm&#39;s fixation region  128  rests in an annular channel  134  on fixation element  110  to provide firm contact between the distal face of the arm fixation region and the fixation element. Alternatively, a second pair of angled washers may be used in place of the partially spherical washer. 
     Similarly, the angle between the right cephalad fixation element  112  and the right support arm  118  may be adjusted and fixed in the adjusted position by rotating two angled washers  136  and  138  mounted on a proximal extension of fixation element  112  between the proximal face  140  of a fixation region  142  on the top end of arm  114  and a compression nut  144  or other tightening element. As on the left side, because each washer  136  and  138  has a contact surface not perpendicular to the axis of fixation element  112 , each washer  136  and  138  may be rotated about fixation element  112  to change the angle between arm  118  (and, therefore, cephalad bearing element  104 ) and fixation element  112 . When the proper orientation has been set, tightening element  144  is tightened along a threaded proximal extension of fixation element  112  to keep the components in place. 
     As on the left side, in this embodiment a partially spherical washer  146  disposed between the distal face  148  of the right cephalad support arm&#39;s fixation region  142  rests in an annular channel  150  on fixation element  112  to provide firm contact between the distal face of the arm fixation region and the fixation element. Once again, a second pair of angled washers may be used in place of the partially spherical washer. 
     An additional adjustment mechanism is provided by the oval shaped openings  152  and  154  of the fixation regions  128  and  142  of left and right cephalad support arms  114  and  118 , respectively. The support arms  114  and  118  may be moved up or down with respect to fixation elements  110  and  112 , respectively, before tightening compression screws  130  or  144  to further adjust the spatial relationships between cephalad facet bearing elements  102  and  104  and fixation elements  110  and  112 . The cephalad support arms  114  and  118  may also be rotated about their respective fixation elements  110  and  112  before tightening. 
     The caudal facet joint prosthesis components may be adjusted with respect to their fixation elements as well. The caudal facet prosthesis bearing elements attach via screws or other fixation elements  160  and  162  to a vertebra inferior to the vertebra to which the cephalad components have been attached. Looking first on the left side, a clamp  164  mounted on fixation element  160  holds a left caudal support bar  166  extending from left caudal bearing surface  106 . Likewise, a clamp  168  mounted on fixation element  162  holds a right caudal support bar  170  extending from right caudal bearing surface  108 . A crossbar  172  extends between the left and right caudal bearing surfaces. 
     In this embodiment, the angle between the left caudal fixation element  160  and the left caudal clamp  164  may be adjusted by rotating a first partially spherical washer  174  (disposed proximal to clamp  464 ) with respect to a cap  179  beneath a compression screw  180  and/or by rotating a second partially spherical washer  176  (disposed distal to clamp  164 ) with respect to an annular channel  178  formed in fixation element  160 . When the proper orientation has been achieved, compression screw  180  or other tightening element is tightened along a threaded proximal extension of fixation element  160  to fix these components in place. Alternatively, a pair of angled washers may be used in place of the partially spherical washers, as in the cephalad component. Likewise on the right side, the angle between the right caudal fixation element  162  and the right caudal clamp  168  may be adjusted by rotating a first partially spherical washer  182  (disposed proximal to clamp  168 ) with respect to a cap  189  beneath a compression screw  188  and/or by rotating a second partially spherical washer  184  (disposed distal to clamp  168 ) with respect to an annular channel  186  formed in fixation element  162 . When the proper orientation has been achieved, compression screw  188  or other tightening element is tightened along a threaded proximal extension of fixation element  162  to fix these components in place. Alternatively, a pair of angled washers may be used in place of the partially spherical washers, as in the cephalad component, as before. 
     Because the various components of the present invention allows for significant adjustment and/or modular variability between the dynamic elements and the fixation elements, the device is particularly well suited for use in virtually all levels of the spine, and for virtually all anatomical variations, including adult males or females or even children. If desired, the fixation elements can incorporate bony in-growth and/or osteo-integration surfaces and/or materials, or the various fixation elements could be utilizes in conjunction with auxiliary fixation materials such as ceramic, crystalline, organic, polymeric or other types of bone cement or adhesives. Where the device fails for some reason, or revision is necessitated (such as, for example, where a young patient “grows out of” the device), a physician could access the device and disassemble those pieces necessary to be replaced, and then reassemble the same or a different size or configuration of the device, or assemble a fusion construct utilizing one or more of the original fixation elements already integrated within and/or attached to the patient&#39;s bones. 
     If desired, the devices of the present invention could be utilized with virtually any dynamic system, including those used in combination with an artificial spinal disc replacement device. Virtually all of the various embodiments disclosed here could be utilized, in various ways, in combination with artificial disc replacement devices, as well as nucleus repair systems and replacement devices, interbody spacers, dynamic stabilization devices, articulating rod and screw systems, posterior ligament or annular repair and/or augmentation devices, interspinous spacers, facet replacement and/or resurfacing devices, and the like. Use of the present devices in a dynamic system, in combination with an artificial disc replacement or repair, provides a solution for the total disc replacement contraindication of facet degeneration. Moreover, implantation of a total disc replacement device after removal of some or all of one or more of the facets and/or other intervening tissues (hard or soft), but prior to implantation of the dynamic device, provides a large, safe and repeatable access to the disc space, as well as aiding in any decompression of the joint that may be necessary. Such access facilitates passage of one or more components of the artificial disc replacement (or nucleus replacement, or annular repair material, and their respective tools) through the removed facet tissues via a lateral, posterior-lateral and/or posterior approach. The functions of the removed tissues can then be replaced by implanting the dynamic device as described herein. Of course, the dynamic devices disclosed herein (and the surgical removal of tissues to create one or more access paths) may be used unilaterally or bilaterally, depending on the nature of and stage of disease, and can be used at multiple levels of the spine of facet and/or other intervening tissues. 
     In various embodiments, a series of artificial dynamic components of differing shapes, sizes and/or orientations and/or lengths can be provided to accommodate different objectives, including alteration of dynamic element height/orientation relative to the fixation element, to accommodate different loading conditions due to other surgical treatments (i.e., artificial disc replacement of the same or other spinal level, annular repair, nucleus replacement, dynamic stabilization, interspinous spacer and/or adjacent level fusion and/or facet replacement devices). Moreover, to accommodate differing designs (i.e., constrained discs versus unconstrained discs) and/or arrangement/positioning of artificial disc replacement devices used on the same or different spinal levels, the dynamic elements could be of differing shapes, sizes, orientations and/or lengths to accommodate the different loading profiles induced or desired by the artificial disc replacement devices. 
     In one alternate embodiment, once the components of the device have been secured to the targeted vertebral bodies, one or more elastic compression devices or “bands” could be secured about the dynamic elements (or to the vertebral bodies themselves, or between other parts of the device, or any combination thereof). Properly positioned and/or tensioned, these “bands” would tend to keep the dynamic elements in contact and/or close proximity, even under extreme and/or unusual loading conditions, and thus reduce and/or eliminate the opportunity for the device to dislocate. Moreover, in the event that dislocation of the device did occur, the bands could prevent and/or limit motion of the dislocated joint (by holding the dynamic elements together), and thus reduce or eliminate damage to other tissues (such as the spinal cord, various other nerves and/or circulatory/connective tissues) resulting from the dislocation. In fact, the compression of the bands might make it possible to eventually “reduce” the dislocation and/or repair the dislocated device through external manipulation and/or minimally-invasive surgery. If desired, one or more “bands” could be secured between the dynamic elements of the device, or between the various surfaces, arms, cups, stems and/or cross-arms of the device components, with varying results. 
     In another alternative embodiment, the compression device could comprise an elastic or pliable material surrounded by a non-elastic housing, whereby the elastic material allows various movement of the dynamic elements (with resistance commensurate to the flexibility of the material), but the non-elastic housing acts as an ultimate “stop” to movement of the dynamic elements beyond a certain pre-determined limit. Similarly, the “band” could comprise an elastic, non-elastic or rigid material, such as stainless steel cable, which desirably prevents relative motion of the elements of the device beyond a certain pre-defined maximum extension/flexion. 
     Advantageously and in contrast to conventional techniques where fusion and dynamic implants are implanted via an open procedure, a majority of the components of the present dynamic devices can be surgically implanted using minimally-invasive techniques alone or in combination with conventional open techniques. For example, all or most of the components of the device may be delivered through a cannula inserted through a small incision in the skin. To implant the device components, the physician can first create an access path through the skin and soft tissue (with a spinal needle and/or K-wire) to the targeted vertebral body. Desirably, non-invasive visualization, such as fluoroscopic or real-time MRI, is used to monitor the advancement of the needle and avoid damage to tissue structures such as muscles, tendons, ligaments, nerves, veins and/or the spinal cord itself. Once the access path has been created, a suitable cannula can be advanced through the tissues to the targeted bone. If necessary, progressively larger dilation catheters (such as the Access™ Dilation Port commercially available from Spinal Concepts of Austin, Tex.) can be used to introduce a cannula having a lumen large enough to accommodate passage of the components. 
     Depending upon the patient&#39;s condition and the desired surgical outcome, as well as the surgeon&#39;s preference, the present embodiment can facilitate the repair and replacement/augmentation of the facet joints in a minimally-invasive, limited-open (or modified-open) and/or fully-open surgical procedure. For example, where facet joint replacement is deemed necessary, but removal of soft and/or hard tissues in and/or adjacent the spinal canal is not warranted or desired (such as where spinal stenosis and nerve impingement is not a significant concern), the repair and/or replacement of one or more facet joints can be accomplished in a least-invasive fashion, using one or more cannulae to implant the prosthesis and associated distal hardware. Alternatively, where removal of the facet joints and/or lamina is necessitated, such a procedure can be accomplished through a combination of open, semi-open and/or minimally invasive procedures (which will be referred to herein as a modified-open or mini-open procedure) to minimize damage and/or disruption to surrounding soft-tissue structures. In such a procedure, one or more of the facet joint capsules can be exposed through an open incision (to allow easy resection and removal of the facet joint and/or surrounding anatomical structures), and the components of the dynamic device can be delivered through a cannula or other minimally-invasive delivery method. 
     Various alternative embodiments of the present invention could incorporate laminar, spinous process, pedicle-based and/or vertebral body fixation elements, or any combinations thereof, ultimately desirous for replacing and/or augmenting the natural facets and other intervertebral tissues. Of course, the systems disclosed herein may be anchored to the vertebral bodies in various ways, including the use of screw threads or stems, with or without using cement and/or bony ingrowth surfaces to augment fixation. 
     While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that methods and structures within the scope of these claims and their equivalents be covered thereby.