Patent Publication Number: US-2022211516-A1

Title: Expanding intervertebral implants

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/902,921 filed on Jun. 16, 2020, which is incorporated in its entirety herein. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to stabilizing adjacent vertebrae of the spine by inserting an intervertebral spacer, and more particularly an intervertebral spacer that is adjustable in height. 
     BACKGROUND OF THE INVENTION 
     The vertebral or spinal column (spine, backbone) is a flexible assembly of vertebrae stacked on top of each other extending from the skull to the pelvic bone which acts to support the axial skeleton and to protect the spinal cord and nerves. The vertebrae are anatomically organized into four generalized body regions identified as cervical, thoracic, lumbar, and sacral; the cervical region including the top of the spine beginning in the skull, the thoracic region spanning the torso, the lumbar region spanning the lower back, and the sacral region including the base of the spine ending with connection to the pelvic bone. With the exception of the first two cervical vertebrae, cushion-like discs separate adjacent vertebrae, i.e. intervertebral discs. 
     The stability of the vertebral column during compression and movement is maintained by the intervertebral discs. Each disc includes a gel-like center surrounded by a fibrous ring. The gel-like center, i.e. nucleus pulposus, provides strength such that the disc can absorb and distribute external loads and contains a mixture of type II-collagen dispersed in a proteoglycan matrix. The fibrous ring, or annulus fibrosus, provides stability during motion and contains laminated rings of type-I collagen. Thus, the annulus fibrosis and the nucleus pulposus are interdependent, as the annulus fibrosis contains the nucleus pulposus in place and the nucleus pulposus aligns the annulus fibrosus to accept and distribute external loads. The integrity of the composition and structure of the intervertebral disc is necessary to maintain normal functioning of the intervertebral disc. 
     Many factors can adversely alter the composition and structure of the intervertebral disc, such as normal physiological aging, mechanical injury/trauma, and/or disease, resulting in impairment or loss of disc function. For example, the content of proteoglycan in the nucleus pulposus declines with age, thus, it follows that the ability of the nucleus pulposus to absorb water concurrently declines. Therefore, in normal aging the disc progressively dehydrates, resulting in a decrease in disc height and possible de-lamination of the annulus fibrosus. Mechanical injury can tear the annulus fibrosis allowing the gel-like material of the nucleus pulposus to extrude into the spinal canal and compress neural elements. Growth of a spinal tumor can impinge upon the vertebrae and/or disc potentially compressing nerves. 
     Bones of the spine, and bony structures, generally, are susceptible to a variety of weaknesses that can affect their ability to provide support and structure. Weaknesses in bony structures have numerous potential causes, including degenerative diseases, tumors, fractures, and dislocations. Advances in medicine and engineering have provided doctors with a plurality of devices and techniques for alleviating or curing these weaknesses. 
     In some cases, the spinal column, in particular, requires additional support in order to address such weaknesses. One technique for providing support is to insert a spacer between adjacent vertebrae. 
     SUMMARY OF THE INVENTION 
     A device of the disclosure for separating bones of a joint using a driver tool having a threaded shaft, comprises a superior endplate having a bone engaging surface and a surface opposite the bone engaging surface having ramps including at least two inferior facing ramps; an inferior endplate having a bone engaging surface and a surface opposite the bone engaging surface having ramps including at least two superior facing ramps; first and second bearings disposed between the first and second endplates, each having ramps including at least one superior facing ramp mateably engaged with an inferior facing ramp of the superior endplate, and at least one inferior facing ramp mateably engaged with a superior facing ramp of the inferior endplate, the first bearing including a threaded aperture, the second bearing including a thrust surface; the threaded aperture threadably engageable with the threaded shaft of the driver tool, the thrust surface aligned with the threaded shaft to be pushable by the threaded shaft when the threaded shaft is threaded through the threaded aperture to thereby cause the first and second bearings to be driven apart, whereby the ramps of the first and second bearings bear against the ramps of the superior endplate and the ramps of the inferior endplate to thereby push the superior endplate away from the inferior endplate. 
     In variations thereof, the threaded aperture disposed at a non-orthogonal angle with respect to a longitudinal axis of the device; at least one of the bone engaging surface of the superior endplate and the bone engaging surface of the inferior endplate having an opening through which bone can grow; the ramps of the first and second bearings and the at least two ramps of the superior endplate and the at least two ramps of the inferior endplate are oriented at a non-orthogonal angle with respect to a longitudinal axis of the device; and/or the first and second bearings are displaced relative to each other along the longitudinal axis of the device when the first and second bearings are pushed apart by the driver. 
     In further variations thereof, the device further includes the threaded driver; the driver includes a threaded end and a handle, the threaded end separable from the handle, whereby the threaded end can remain with the device within the body; a leading end of at least one of the superior endplate and the inferior endplate provided with an angular profile, whereby a leading end of the device has a tapering leading end profile; the threaded aperture forming an acute angle with respect to a longitudinal axis of the device which opens in a direction away from the leading end; and/or the device includes no more than 5 parts, limited to the superior and inferior endplates, the first and second bearings, and the threaded shaft. 
     In yet further variations thereof, the device further includes a radiopaque material; the superior and inferior endplates, and the first and second bearings all mutually nest when the device is in a collapsed configuration to thereby present a reduced radial profile to facilitate insertion of the device into a patient; and/or ramps of the bearings being at least one of recessed relative to a surrounding surface and projecting relative to a surrounding surface, wherein when a mating ramp of the superior endplate and a mating ramp of the inferior endplate are mated to a recessed bearing ramp, the mating ramp is projecting relative to a surrounding surface, and when a mating ramp of the superior endplate and a mating ramp of the inferior endplate are mated to a projecting bearing ramp, the mating ramp is recessed relative to a surrounding surface. 
     In a method of the disclosure, separating bones of a joint comprises inserting a spacer through an opening in Kambin&#39;s triangle, the spacer having: a superior endplate having a bone engaging surface and a surface opposite the bone engaging surface having ramps including at least two inferior facing ramps; an inferior endplate having a bone engaging surface and a surface opposite the bone engaging surface having ramps including at least two superior facing ramps; first and second bearings disposed between the first and second endplates, each having ramps including at least one superior facing ramp mateably engaged with an inferior facing ramp of the superior endplate, and at least one inferior facing ramp mateably engaged with a superior facing ramp of the inferior endplate, the first bearing including a threaded aperture, the second bearing including a thrust surface; the threaded aperture threadably engageable with the threaded shaft of the driver tool, the thrust surface aligned with the threaded shaft to be pushable by the threaded shaft when the threaded shaft is threaded through the threaded aperture to thereby cause the first and second bearings to be driven apart, whereby the ramps of the first and second bearings bear against the ramps of the superior endplate and the ramps of the inferior endplate to thereby push the superior endplate away from the inferior endplate; rotating the driver tool to cause pushing of the inferior endplate away from the superior endplate to restore a therapeutic alignment of the bones of the joint; removing the driver tool to leave the threaded shaft within the device. 
     In variations thereof, the spacer has a tapered leading end, the threaded aperture disposed at an acute angle opening in a direction away from the tapered leading end, the method further including pushing the device into the body using a tool engaged with the threaded aperture; the ramps of the first and second bearings and the at least two ramps of the superior endplate and the at least two ramps of the inferior endplate are oriented at a non-orthogonal angle with respect to a longitudinal axis of the device, the method further including rotating the driver tool to cause displacement of the first and second bearings relative to each other along the longitudinal axis of the device; and/or the driver tool having a handle coupled to the threaded shaft, the method further including uncoupling the handle from the threaded shaft. 
     In other variations thereof, the method further includes selecting an endplate from among a plurality of endplates each having a relatively different lordotic profiles; the spacer including opening to an interior of the spacer, the method further including inserting a bone growth material into the opening; and/or the bone growth material selected from at least one of an autograft, allograft, xenograft, and bone substitute. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the disclosure, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a front perspective view of a spacer device of the disclosure; 
         FIG. 2  is a lower perspective view of the device of  FIG. 1 ; 
         FIG. 3  is a rear perspective view of the device of  FIG. 1 ; 
         FIG. 4  is a front perspective view of an opposite side of the device of  FIG. 1 , in an expanded configuration; 
         FIG. 5  is a front perspective view of the device of  FIG. 1 , radially rotated, and in an expanded configuration; 
         FIG. 6  is a rear perspective view of the device of  FIG. 1 , in an expanded configuration; 
         FIG. 7  is a perspective view of the device of  FIG. 1 , in an expanded configuration, including a driver tool threaded into the device; 
         FIG. 8  is an alternative perspective of the device of  FIG. 7 ; 
         FIG. 9  is an exploded perspective view of the device of  FIG. 7 ; 
         FIGS. 10-11  are perspective views of a bearing of the device of  FIG. 1 , which includes a threaded through-bore engageable with the driver tool; 
         FIGS. 12-13  are perspective views of another bearing of the device of  FIG. 1 , which includes a thrust surface aligned with the through-bore of the bearing of  FIGS. 10-11 ; 
         FIGS. 14-15  are perspective views of a superior endplate of the device of  FIG. 1 ; 
         FIGS. 16-17  are perspective views of an inferior endplate of the device of  FIG. 1 ; 
         FIG. 18  is a diagrammatic view of the device of  FIG. 1  in position upon a bone surface, the device having been inserted into the body using a cannula tool; 
         FIG. 19-20  are alternative perspective view of the device and bone of  FIG. 18 ; and 
         FIG. 21  is a perspective view of the device and bone of  FIG. 18 , with an expansion driver tool mounted within the device and extending outside of the body. 
         FIGS. 22 and 23  illustrate a handle with a coupling portion; 
         FIGS. 24 and 25  illustrate the coupling portion; 
         FIG. 26  illustrates a castle nut portion according one embodiment of the invention; and 
         FIG. 27  illustrates the device in an expanded configuration. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As required, detailed embodiments are disclosed herein; however, it is to be understood that the disclosed embodiments are merely examples and that the systems and methods described below can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present subject matter in virtually any appropriately detailed structure and function. Further, the terms and phrases used herein are not intended to be limiting, but rather, to provide an understandable description of the concepts. 
     The terms “a” or “an”, as used herein, are defined as one or more than one. The term plurality, as used herein, is defined as two or more than two. The term another, as used herein, is defined as at least a second or more. The terms “including” and “having,” as used herein, are defined as comprising (i.e., open language). 
     With reference to the figures, the disclosure provides an expandable spacer/implant or device  100  having an adjustable height. Device  100  is inserted between two adjacent bony surfaces to facilitate separation of the bones, and if desired, to promote the fusion of bony surfaces. Although intended to be useful with any adjacent bony surface in which fusion is desired, device  100  is advantageously applied to insertion between two adjacent vertebral bodies in any section of the spine, including the cervical, thoracic, lumbar, and sacral vertebral sections. More than one device  100  may be implanted within the body, for example between successive or separated vertebrae, or positioned between the same adjacent vertebrae. The use of multiple devices  100  is particularly advantageous for patients whose back pain is not limited to a localized area, or for patients whose localized damage has progressed to other areas of the spine. 
     Device  100  and methods for its insertion can be used in a treatment protocol for any of a wide variety of conditions in a patient involving diseased or damaged bony structures. The patient can be a human being. Additionally, it is contemplated that device  100  may be useful in veterinary science for any animal having adjacent bony structures to be fused. Devices  100  can expand to roughly twice its fully reduced insertion height. When in this collapsed configuration, device  100  can be inserted into a space through a small incision and narrow pathways, using appropriate minimally-invasive techniques, and can be positioned within the space between adjacent bones, and there expanded to a desired therapeutic height. The incision may be short, for example about one centimeter in length, which is smaller than device  100  in an expanded configuration. If the desired position and/or expansion are not achieved, device  100  can be collapsed, repositioned, and re-expanded in situ. 
     Although device  100  is exemplified herein for use in the spine, device  100  is contemplated for fusion of any bony structures. While devices  100  are described herein using several varying embodiments, devices  100  are not limited to these embodiments. An element of one embodiment may be used in another embodiment, or an embodiment may not include all described elements. 
     Interbody devices have been used to provide support and stability in the anterior column of the spinal vertebrae when treating a variety of spinal conditions, including degenerative disc disease and spinal stenosis with spondylolisthesis. Clinical treatment of spinal pathologies with anterior vertebral body interbody devices relies on precise placement of interbodies to restore normal anterior column alignment. Iatrogenic pathologies may result from both the surgical access window to the disc space, failure to precisely place the interbody on hard cortical bone often found on the apophyseal ring of the vertebral body, or failure to precisely control and restore normal anatomical spinal alignment. Device  100  provides for the precise placement of interbody support that both increases interbody contact with hard cortical bone and provides precise control of anterior column alignment while reducing the profile of the access window to the disc space. 
     More particularly, in order to improve the access profile of the interbody while maximizing cortical bone contact surface area, device  100  enters the disc space with a narrow profile and can be positioned upon the anterior apophyseal ring. The orientation and position of the interbody in its final implanted position may be optimized by pre-/intra-op scans or normal population statistics that determine bone mineral density maps of the vertebral body. Robotic and navigation guidance may be used to correctly orient the interbody. 
     In an embodiment, device  100  can be implanted as follows: 
     1. A determination is made on final optimal implant location to optimize bone mineral density of the contacted bone/implant interface. 
     2. Robotic/navigation is used to determine the potential trajectories that will allow for this optimal implant location to be achieved. 
     3. A cannula is docked on the disc space through Kambin&#39;s triangle, or the anatomical area that is bordered by the disc space, exiting nerve root, and traversing nerve root. 
     4. The expandable interbody is inserted in the non-expanded orientation ( FIGS. 1-3 ) into contact with, for example, the anterior apophyseal ring of the vertebral body ( FIGS. 7-8, 21, and 27 ). 
     5. The expandable interbody is expanded to precisely achieve a therapeutic spinal alignment. 
     With reference to the drawings, device  100  is expanded using a slide system which causes the separation of endplates  120  and  122 , which are each positioned within the body to contact a separate side of a bone joint relative to the other endplate. When positioned within the spine, one endplate will be a superior endplate contacting a more superior vertebra, and the other endplate will be an inferior endplate, contacting a more inferior vertebra. An orientation of device  100  may be determined by the side of the body from which implantation is approached. For convenience, herein, endplate  120  will be designated as superior, although it should be understood that endplate  122  could be designated as superior. 
     In particular, and with reference to  FIGS. 4-6 , device  100  includes first and second internal bearings  102 ,  104  each having one or more superior facing ramps  106 A, and one or more inferior facing ramps  106 B (collectively ramps  106 ). In the figures, ramps  106  are illustrated as being recessed relative to surrounding surfaces, however one or all of ramps  106  can alternatively project from surrounding surfaces. Ramps  106 A extend transverse to the central longitudinal axis of device  100  and are angled from an inferior position distal to the central longitudinal axis to a superior position proximal to the central longitudinal axis. Ramps  106 B likewise extend transverse to the central longitudinal axis of device  100  but are angled from a superior position distal to the central longitudinal axis to an inferior position proximal to the central longitudinal axis. 
     Bearing  104  includes a threaded through-bore  108  disposed at an angle relative to the central longitudinal axis of device  100 . Bearing  102  includes a thrust surface  110 , in the embodiment shown having the form of a blind-hole or capture bore that is axially aligned with through-bore  108 . A driver  112  including a handle  136  and a separable set screw  138  can be threaded into through-bore  108  to then pass into thrust surface  110  and can rotate within thrust surface  110  as driver  112  is rotated to thereby cause bearings  102  and  104  to be forced apart to expand device  100 , as described further below. After expansion, handle  136  can be separated from set screw  138  at coupling  140 . As bearing  104  is contacted by driver  112 , it would typically be considered the proximal bearing, and bearing  102  the distal bearing. 
     By forming thrust surface as a bore, driver  112  is captured by both bearings  102 ,  104 , to thereby maintain a predetermined orientation and alignment of bearings  102 ,  104  as they move relative to each other. Thrust surface  110  can alternatively have the form of a flat surface, and another form of guide for bearings  102 ,  104  can be provided, such as one or more rails (not shown) extending between or through bearings  102 ,  104 . 
     Endplates  120 ,  122  each include a bone facing outer side  114  and a mutually facing inner side  116 . Each inner side  116  of endplate  120  includes one or more inferior facing ramps  126 B, and each inner side  116  of endplate  122  includes one or more superior facing ramps  126 A. In the figures, ramps  126  are illustrated as projecting relative to surrounding surfaces, however one or all of ramps  126  can alternatively be recessed from surrounding surfaces. However, where ramps  106  project, ramps  126  advantageously are recessed, whereby this inverse relationship helps to maintain an axial alignment between ramps  106  and  126  when mutually engaged. Ramps  126 A extend transverse to the central longitudinal axis of device  100  and are angled from an inferior position distal to the central longitudinal axis to a superior position proximal to the central longitudinal axis. Ramps  126 B likewise extend transverse to the central longitudinal axis of device  100  but are angled from a superior position distal to the central longitudinal axis to an inferior position proximal to the central longitudinal axis. 
     Endplates  120 ,  122  and bearings  102 ,  104  are collectively engaged to form an assembled device  100  by mating endplate ramps  126 A with bearing ramps  106 A, and mating endplate ramps  126 B with bearing ramps  106 B. In a collapsed configuration of device  100 , ramps  106 A and ramps  126 A are engaged over a greater mutual surface than when device  100  is in an expanded configuration. To cause expansion, driver  112  is threaded into through-bore  108  to bear against thrust surface  110 , and to thereby cause separation of bearings  102 ,  104  as driver  112  is further rotated. As bearings  102 ,  104  separate, ramps  126 A are driven superiorly against ramps  106 A, and ramps  126 B are driven inferiorly against ramps  106 B. As a result, endplates  120  and  122  are mutually separated, increasing a height of device  100 . 
     Ramps  106  can be of equal shape and size, and ramps  126  can be of equal shape and size, and bone facing outer side  114  of bearings  120  and  122  can be parallel when collapsed, whereby the bone facing sides  114  of endplates  120  and  122  will remain parallel as device  100  is expanded. Alternatively, ramps  106  and  126  can have alternative shapes which cause unequal expansion which can be used to adjust for lordosis. The unequal expansion can be caused, by the ramp  106 ,  126  shapes and sizes, to occur along the long axis of device  100 , or along an axis transverse to the long axis of device  100 . Alternatively, bone facing sides  114  of endplates  120 ,  122  can be non-parallel when collapsed, and this non-parallel relationship can be maintained during expansion by equal ramp  106 ,  126  shapes and sizes, or the non-parallel relationship can be changed during expansion by unequal ramp  106 ,  126  shapes and sizes. 
     As can best be seen in  FIGS. 1-3 , ramps  106  and  126  are sized and dimensioned to nest, for example along line  132 , as completely as possible, so that a collapsed profile of device  100  is as small as possible. When collapsed, device  100  is provided with a tapered leading end  124  which facilitates insertion of device  100  into the body. Tapering leading end  124  is formed from a leading portion  128  of endplate  120  and a leading portion  130  of endplate  122 , which are mutually adjacent when device  100  is collapsed, as would be the case during implantation. 
     Advantages of the disclosure include, at least: 
     1. A small insertion profile: The disclosure enables, for example, an 8.5 mm insertion profile into the disc space, reducing the required skin, fascia, muscle, and ligamentous disruption. Smaller profiles can be achieved, including profiles as small as 6 mm, for example, or profiles substantially larger than 8.5 mm, in each case limited only by the needs dictated by a particular patient&#39;s anatomy. 
     2. Controlled lordosis: The disclosure enables controlled lordosis through placement of device  100  in a collapsed position on the anterior apophyseal ring within the disc space. With the spacer placed horizontally across the disc space, and due to the fact that the spacer has a relatively small depth, the spacer can be used in one application as a fulcrum to increase lordosis as it is expanded, if therapeutically beneficial. It is generally accepted that placing the spacer on the anterior apophyseal ring provides the most leverage for continuously increasing lordosis as it is expanded in height. However, more posterior placement can also be utilized as this can allow for increased anterior height when leveraging using the same height spacer. Alternatively, two devices  100  can be placed between the same vertebrae, one in the anterior aspect of the vertebral body and one in the posterior aspect of the vertebral body, to further control and adjust sagittal balance by then allowing independent expansion of the anterior and posterior aspects of the vertebral body. 
     3. Reduced endplate disruption: Due to the ability of device  100  to expand a correct, therapeutic extent in situ, the disclosure reduces the need for traditional trialing through the insertion of interbody implants of various sizes, the latter potentially causing or contributing to vertebral endplate disruption and further trauma to the body. 
     With reference to  FIGS. 18-21 , an implantation tool  400  forms a cannula. Indicia  402  indicate an insertion depth of tool  400  into the body. Positioning is carried out using imaging, and can further be carried out using a robotics system. The bore  404  of tool  400  enables the insertion of surgical instruments in order to cut, excise, or cauterize body tissue, and to otherwise facilitate a surgical procedure to implant device  100 . Bore  404  is further sized to enable passage of device  100 . To minimize the required size of bore  404 , device  100  is configured in the collapsed configuration, which is the smallest height profile, with driver  112  disengaged. 
     After device  100  exits tool  400  within the body, it may be manipulated into a position upon the vertebral endplate  300 , for example upon the apophyseal ring  302 , using surgical tools passed through tool  400 . After device  100  is positioned, driver  112  is passed through tool  400  and engaged with through-bore  108 . Alternatively, tool  400  is removed prior to insertion of driver  112 . Tool  400  can be removed after engagement between driver  112  and through-bore  108 , as determined by the practitioner and the applicable protocol. 
     Engaged driver  112  can be rotated to cause expansion of device  100  as described above. At a later date, if needed, tool  400  can be reinserted into the body to reposition device  100 , change a height of device  100  using driver  112 , and/or device  100  can be removed from the body if therapeutically beneficial. With reference to  FIGS. 22-26 , a coupling  140  enables separation of driver handle portion  136  and set screw  138 . In  FIGS. 22-23 , handle  136  includes a coupling portion  142  which includes an internal thread mateable with set screw  138 , whereby after set screw  138  is fully engaged, further rotation of handle  136  causes rotation of set screw  138 . Rotating handle  136  in an opposite direction disengages handle  136  from set screw  138 . Set screw  138  includes a tool engagement  144  which can be used to reverse rotation of set screw  138 , for example to collapse device  100 , or to prevent rotation of set screw  138  as handle  136  is unthreaded from set screw  138 . To engage set screw  138 , a tool is inserted through a central bore  150  through handle  112  and coupling  140 . A hex engagement is illustrated, although any other suitable type of engagement can be used. 
     Device can be passed into the body with tapering leading end  124  inserted first. The chamfered or tapering profile of leading end  124 , which can be different than the profile illustrated, reduces disruption and potential trauma to the body by having smooth rounded edges, and by gradually separating tissue due to the tapered profile. Accordingly, device  100  is advantageously passed into the body in a leading end  124  first orientation. 
     In place of implantation tool  400 , driver  112  can be threaded into through-bore  108 , after which driver  112  can be used to manipulate device  100  into a desired position within the body. In the illustrations, through-bore  108  and thrust surface  110  are angularly disposed within bearings  102 ,  104  to enable driver  112  to be inserted through a, typically, separate pathway to device  100  within the body. As can be seen best in  FIGS. 1 and 7 , driver  112  must be threaded into through-bore  108  by approaching from a direction passing towards leading end  124 . As such, the angular disposition of the through-bore forms an acute angle with the longest longitudinal axis of the device, which opens in a direction towards leading end  124 . 
     However, with reference to  FIG. 27 , it may be seen that through-bore  108  and thrust surface  110  can be positioned anywhere along bearings  102 ,  104 , and can be disposed at other angular orientations. As shown in  FIG. 27 , through-bore  108  and thrust surface  110  are now positioned further from leading end  124 , and are angled in an opposite direction, with respect to depictions in other figures herein. As such, the angular disposition of the through-bore forms an acute angle with the longest longitudinal axis of the device, which opens in a direction away from leading end  124 . This positions and angles driver  112 , when threaded into through-bore  108 , to approach through the same pathway into the body as device  100 . Moreover, driver  112  can function as an implantation tool which can be used to manipulate device  110  into a therapeutic position within the body. After implantation in this manner, and without a requirement of removing driver  112  or changing tools, driver  112  can further function to be rotated to increase a height of device  100  to address skeletal stability. After adjusting a height of device  100 , handle  136  is removed as described with respect to  FIGS. 22-26 , or in some other manner. 
       FIG. 27  further depicts device  100  in an expanded configuration, wherein it may be seen that bearings  102  and  104  have become relatively displaced along the longitudinal axis of device  100 , as a result of being driven apart. Accordingly, ramps  106 ,  126  must be relatively sized and/or angularly disposed to enable this longitudinal displacement of bearings  102 ,  104 . As can best be seen, for example, in  FIG. 12 , bearing ramps  106 A,  106 B are disposed at a non-orthogonal angle with respect to a longitudinal axis of device  100 , the longitudinal axis being the longest axis of device  100 , which extends from leading end  124  to trailing end  152  ( FIG. 1 ). Ramps  126  of the superior and inferior endplates are angled to mate with the angle of ramps  106 , to thereby enable relative movement of the bearings along the longitudinal axis when bearings  102 ,  104  are separated by being driven apart by driver  112 . 
     As can additionally be seen in  FIGS. 10-13 , sidewalls  154  of ramps  106 A,  106 B can optionally be provided with dovetail surfaces which mate with dovetailed surfaces of ramps  126 A,  126 B (not shown in dovetail form). This can help to ensure that endplates  120 ,  122  remain in engagement with bearings  102 ,  104 . 
     In  FIGS. 24-25 , coupling  140 A includes a castle nut end portion  146  on set screw  138 , and a mating castle nut end portion  148  on handle  136 .  FIG. 26  depicts a castle nut portion  146 A which can be removed from set screw  138 . 
     Different devices  100  may include ramps  106 ,  126  of differing height and length relative to other devices  100 , to enable expansion at different rates or extents, as indicated for therapeutic treatment. Fewer or a greater number of ramps  106 ,  126  can be provided. Endplates  120 ,  122  may additionally, or alternatively, be resilient, so that they may conform to bony surfaces, forming a more stable support platform. Accordingly, endplates  120 ,  122  can be fabricated from a polymeric material, a naturally resilient material, or a resilient metal, for example a shape memory alloy, or any other resilient biocompatible material of sufficient strength and durability for separating bones within the body. 
     Device  100  can be inserted at a contracted height transforaminally, for example, and is capable of being positioned into anterior placement. Once placement is achieved, device  100  is capable of expanding for disc height restoration. Additionally, device  100  can be positioned anteriorly, and can be expanded through a continuous range to provide axial balance and greater endplate contact area. Additionally, device  100  enables superior sagittal correction, through the use of a relatively smaller insertion window, decreasing the need for bone damage. Thus, device  100  provides the benefits of an ALIF device through a familiar posterior approach, decreasing surgery time and associated blood loss, as well as eliminating the need for an access surgeon. 
     In accordance with the disclosure, during implantation of intervertebral spacers from a posterior approach, there is a need to avoid damaging nerve roots. A prior art spacer dimensioned to separate bones can block a view of nerve roots as it is inserted, and due to its large size, poses a greater risk of contacting nerve roots during insertion into the body. As a result, the medical practitioner must more often retract nerve roots, with attendant danger of tissue damage. Devices  100  of the disclosure form a smaller dimension during implantation, relative to a final dimension for spacing bones. Accordingly, nerve roots can be visualized and avoided during insertion, and nerve root manipulation can be avoided or minimized. 
     As devices  100  of the disclosure have a much smaller collapsed profile, they can be inserted between bones by being passed through a minimally invasive entry, for example through an incision approximating the smallest collapsed dimension, for example transverse to the longitudinal dimension. This enables exceptional anterior placement without impaction, as well as facilitating implantation from other approaches. Devices  100  of the disclosure further develop a good bone contact area, as an implant with a larger footprint may be inserted through a reduced size incision, due to the overall dimensions of device  100  being reduced during insertion. 
     Devices  100  of the disclosure enable a continuous expansion and distraction over a range of displacements according to predetermined dimensions of a specific spacer design. This provides the ability to distract vertebral bodies or other bones to a desired height or separation. Endplates  120 ,  122  can be shaped to form planes or surfaces which converge relative to each, to provide for proper lordosis, and can be provided with openings  134  through which bone ingrowth may grow, and into which bone graft material may be placed. Devices  100  of the disclosure may be used to distract, or force bones of a joint apart, or may be used to maintain a separation of bones created by other means, for example by a retractor. Endplates may additionally be curved to conform to the surface of body tissue, for example the surface of cortical bone, of the vertebra to be contacted, for improved fixation and load bearing. 
     Devices  100  of the disclosure may be further secured in connection with the body by passage of elongated fasteners through an endplate  120 ,  122 . A blocking mechanism can be used to prevent backing out of an elongated fastener. 
     Devices  100  of the disclosure may be fabricated using any biocompatible materials known or hereinafter discovered, having sufficient strength, flexibility, resiliency, and durability for the patient, and for the term during which the device is to be implanted. Examples include but are not limited to metal, such as, for example titanium and chromium alloys; polymers, including for example, PEEK or ultra high molecular weight polyethylene (UHMWPE); and ceramics. There are many other biocompatible materials which may be used, including other plastics and metals, as well as fabrication using living or preserved tissue, including autograft, allograft, and xenograft material. 
     Portions or all of device  100  may be radiopaque or radiolucent, or materials having such properties may be added or incorporated into device  100  to improve imaging of the device during and after implantation. 
     Devices  100  may be formed using titanium, or a cobalt-chrome-molybdenum alloy, Co—Cr—Mo, for example as specified in ASTM F1537 (and ISO 5832-12). The smooth surfaces may be plasma sprayed with commercially pure titanium, as specified in ASTM F1580, F1978, F1147 and C-633 (and ISO 5832-2). Alternatively, part or all of devices  100  may be formed with a polymer, for example ultra-high molecular weight polyethylene, UHMWPE, for example as specified in ASTM F648 (and ISO 5834-2). In one embodiment, PEEK-OPTIMA (a trademark of Invibio Ltd Corp, United Kingdom) may be used for one or more components of devices  100  of the disclosure. For example, polymeric portions can be formed with PEEK-OPTIMA, which is radiolucent, whereby bony ingrowth may be observed. Other polymeric materials with suitable flexibility, durability, and biocompatibility may also be used. 
     In accordance with the invention, devices  100  of various sizes may be provided to best fit the anatomy of the patient. Components of matching or divergent sizes may be assembled during the implantation procedure by a medical practitioner as best meets the therapeutic needs of the patient, the assembly inserted within the body using an insertion tool. Devices  100  of the invention may also be provided with an overall angular geometry, for example an angular mating disposition of endplates, to provide for a natural lordosis, or a corrective lordosis, for example of from 0° to 12° for a cervical application, although much different values may be advantageous for other joints. Lordotic angles may also be formed by shaping one or both endplates to have relatively non-coplanar surfaces. 
     A kit can be provided which includes a plurality of either or both of endplates and bearings having differing lordotic profiles of uneven height along their length. The medical practitioner can select among the differing profiles to provide an optimal lordotic adjustment for the patient, the selection taking place during the surgical procedure. 
     Expanded implant heights, for use in the cervical vertebrae for example, may typically range from 7 mm to 12 mm, but may be larger or smaller, including as small as 5 mm, and as large as 16 mm, although the size is dependent on the patient, and the joint into which an implant of the invention is to be implanted. Devices  100  may be implanted within any level of the spine, and may also be implanted in other joints of the body, including joints of the hand, wrist, elbow, shoulder, hip, knee, ankle, or foot. 
     In accordance with the invention, a single device  100  may be used, to provide stabilization for a weakened joint or joint portion. Alternatively, a combination of two, three, or more of any of device  100  may be used, at a single joint level, or in multiple joints. Moreover, implants of the disclosure may be combined with other stabilizing means. 
     Additionally, devices  100  of the disclosure may be fabricated using material that biodegrades in the body during a therapeutically advantageous time interval, for example after sufficient bone ingrowth has taken place. Further, implants of the disclosure are advantageously provided with smooth and or rounded exterior surfaces, which reduce a potential for deleterious mechanical effects on neighboring tissues. 
     Any surface or component of a device  100  of the disclosure may be coated with or impregnated with therapeutic agents, including bone growth, healing, antimicrobial, or drug materials, which may be released at a therapeutic rate, using methods known to those skilled in the art. 
     Devices of the disclosure provide for adjacent vertebrae to be supported during flexion/extension, lateral bending, and axial rotation. In one embodiment, device  100  is indicated for spinal arthroplasty in treating skeletally mature patients with degenerative disc disease, primary or recurrent disc herniation, spinal stenosis, or spondylosis in the lumbosacral spine (LI-ST). Degenerative disc disease is advantageously defined as discogenic back pain with degeneration of the disc confirmed by patient history and radiographic studies, with or without leg (radicular) pain. Patients are advantageously treated, for example, who may have spondylolisthesis up to Grade 1 at the involved level. The surgery position device  100  may be performed through an Anterior, Anterolateral, Posterolateral, Lateral, or any other approach. 
     In a typical embodiment, devices  100  of the disclosure have an uncompressed height, before insertion, of 7 to 13 mm, and may advantageously be provided in cross-sections of 8×22, 8×26, 8×30, 8×34, 10×27 mm, 12×32 mm and 12×37 mm, and can optionally be provided with 4, 8, 12, 15, 20, 25, or 30 degree lordotic angles, although these are only representative sizes, and substantially smaller or larger sizes can be therapeutically beneficial. In one embodiment implants in accordance with the instant disclosure are sized to be inserted using an MIS approach, for example using a reduced incision size, for example less than about 5 cm, and advantageously less than about 1 cm, with fewer and shorter cuts through body tissue. Device  100  may advantageously be used in combination with other known or hereinafter developed forms of stabilization or fixation, including for example rods and plates, or intradiscal fixation, potentially connecting device  100  to one or more of the adjacent vertebrae. 
     Devices  100  of the disclosure can be inserted into the body, advantageously in a contracted or non-expanded configuration, through a transforaminal approach, and can be positioned in attachment to an inserter tool, for example as shown in  FIGS. 18-21 , or by using another tool, for example for anterior placement. Once placement is achieved, device  100  is capable of expanding for disc height restoration. To maintain an engagement device  100  and an insertion tool, a driving end (not shown) of the tool can be engaged with device  100 , for example by a threaded coupling. 
     All references cited herein are expressly incorporated by reference in their entirety. There are many different features of the present disclosure and it is contemplated that these features may be used together or separately. Unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. Thus, the disclosure should not be limited to any particular combination of features or to a particular application of the disclosure. Further, it should be understood that variations and modifications within scope of the disclosure might occur to those skilled in the art to which the disclosure pertains. Accordingly, all expedient modifications readily attainable by one versed in the art from the disclosure set forth herein that are within the scope of the present disclosure are to be included as further embodiments of the present disclosure.