Expandable intervertebral implant

[0001] The present application is a divisional of U.S. patent application Ser. No. 12/072,912, filed Feb. 28, 2008, the disclosure of which is incorporated herein by reference.

[0002] Surgeons are performing more and more spinal surgeries to correct different spinal defects in the hopes of reducing pain and restoring normal or close to normal movement. One area of particular interest lies in the restoration of normal spacing between adjacent vertebral bodies. Whether due to the degeneration of the intervertebral disc over time or because of an injury, a decrease in spacing between vertebral bodies can cause a myriad of problems for a patient, the least of which is pain resulting from the pinching of nerves between the bodies. Correcting this problem is often very important to returning a patient to his or her normal level of activity and/or managing the pain associated with a degenerative spinal problem.

[0003] Over the years, there have been many different techniques employed in restoring the normal disc space. For instance, solid fusion devices have been implanted in many patients in the hopes of both restoring normal disc spacing and preventing further degeneration of the space by fusing the vertebral bodies to one another. Recently, there has been a trend to both restore the disc spacing and allow natural movement of the adjacent vertebral bodies with respect to one another. Nonetheless, there exist certain extreme cases of degradation of the disc space which require extreme measures in order to restore the natural spacing.

[0004] Often, the decrease in spacing will be so drastic that some amount of distraction of the adjacent vertebral bodies will be required. Although this distraction is sometimes achieved through the use of various tools, the desire for faster and more efficient surgical techniques favors the elimination of superfluous surgical steps. Thus, there exists a need for an intervertebral implant which is implantable in an unexpanded state and easily expandable to restore the disc space, thereby negating the need for additional tools and the additional surgical steps of using them.

[0005] A first aspect of the present invention is an expandable implant for implantation between two vertebral bodies. In a first embodiment of this first aspect, the implant includes a first member, the first member including a first vertebral contact surface and a first interior surface, a second member, the second member including a second vertebral contact surface and a second interior surface, the first and second interior surfaces facing towards one another, a strut attached to both the first and second members, and a wedge disposed between the first and second interior surfaces and attached to at least one of the first or second members. Preferably, in this embodiment, movement of the wedge in a first direction causes movement of at least one of the first or second members in a second direction.

[0006] In other embodiments of the first aspect, the wedge may be attached to at least one of the first or second members by a deformable tether. The implant may include first and second wedges, where movement of the first and second wedges towards one another causes an increase in a distance between the first and second interior surfaces. The first and second wedges may each be attached to both of the first and second members by a deformable tether. Additionally, one of the first or second wedges may include a bulleted or rounded surface for aiding in insertion of the expandable implant between the two vertebral bodies. Further, the first wedge may include first and second angled wedge surfaces for cooperating with first and second angled interior surfaces of the first and second members respectively, the second wedge may include third and fourth angled wedge surfaces for cooperating with third and fourth angled interior surfaces of the first and second members respectively, and movement of the first and second wedges towards one another may be permitted, while movement of the first and second wedges away from one another is prevented. This may be the case because the first, second, third, and fourth wedge surfaces and the first, second, third, and fourth interior surfaces may each include teeth. The first and second members and the first and second wedges may also cooperate to define at least one aperture through the implant adapted for bone growth therethrough.

[0007] A second aspect the present invention may be another expandable implant for implantation between two vertebral bodies. In one embodiment according to this second aspect, the implant may include a first member, the first member including a first vertebral contact surface and a first interior surface, a second member, the second member including a second vertebral contact surface and a second interior surface, the first and second interior surfaces facing towards one another, a strut attached to both the first and second members, and first and second wedges disposed between the first and second interior surfaces, one of the first or second wedges including a bulleted or rounded surface for aiding in insertion of the expandable implant between the two vertebral bodies. Preferably, in this embodiment, movement of the first wedge towards the second wedge causes an increase in a distance between the first and second interior surfaces.

[0008] In other embodiments of the second aspect, each of the first and second wedges is attached to each of the first and second members by deformable tethers. The first wedge may include first and second angled wedge surfaces for cooperating with first and second angled interior surfaces of the first and second members respectively, the second wedge may include third and fourth angled wedge surfaces for cooperating with third and fourth angled interior surfaces of the first and second members respectively, and movement of the first and second wedges towards one another may be permitted, while movement of the first and second wedges away from one another is prevented. This may be the case because the first, second, third, and fourth wedge surfaces and the first, second, third, and fourth interior surfaces each include teeth. Furthermore, the first and second members and the first and second wedges may cooperate to define at least one aperture through the implant adapted for bone growth therethrough.

[0009] A third aspect of the present invention may be another expandable implant for implantation between two vertebral bodies. According to one embodiment of this third aspect, the implant may include a first member, the first member including a first vertebral contact surface and a first interior surface, a second member, the second member including a second vertebral contact surface and a second interior surface, the first and second interior surfaces facing towards one another, a strut attached to both the first and second members, and first and second wedges disposed between the first and second interior surfaces. Preferably, in this embodiment, movement of the first wedge towards the second wedge causes an increase in a distance between the first and second interior surfaces, and at least one of the first and second wedges is prevented from torsionally moving with respect to the first and second members.

[0010] In other embodiments of the third aspect, each of the first and second wedges may be attached to each of the first and second members by deformable tethers. The first wedge may include first and second angled wedge surfaces for cooperating with first and second angled interior surfaces of the first and second members respectively, the second wedge may include third and fourth angled wedge surfaces for cooperating with third and fourth angled interior surfaces of the first and second members respectively, and movement of the first and second wedges towards one another may be permitted, while movement of the first and second wedges away from one another is prevented. This may be the case because the first, second, third, and fourth wedge surfaces and the first, second, third, and fourth interior surfaces may each include teeth. Further, the first and second members and the first and second wedges may cooperate to define at least one aperture through the implant adapted for bone growth therethrough. Still further, the first and second members may include either a depression or a protuberance, and the first and second wedges may include the other of a depression or a protuberance. The first and second members may include a tongue, a pin, or an elongate projection, and the first and second wedges may include either a groove or a channel.

[0011] A fourth aspect of the present invention is another expandable implant for implantation between two vertebral bodies. One embodiment of this fourth aspect includes a first member, the first member including a first vertebral contact surface and a first interior surface having a first and third angled interior surfaces, a second member, the second member including a second vertebral contact surface and a second interior surface having second and fourth angled interior surfaces, the first and second interior surfaces facing towards one another, a strut attached to both the first and second members, a first wedge disposed between the first and second interior surfaces, the first wedge including first and second angled wedge surfaces for cooperating with the first and second angled interior surfaces of the first and second members respectively, and a second wedge disposed between the first and second interior surfaces, the second wedge including third and fourth angled wedge surfaces for cooperating with the third and fourth angled interior surface of the first and second members respectively. Preferably, in this embodiment, movement of the first wedge towards the second wedge causes an increase in a distance between the first and second interior surfaces, and movement of the first and second wedges towards one another may be permitted, while movement of the first and second wedges away from one another is prevented.

[0012] In other embodiments of the fourth aspect, the first, second, third, and fourth wedge surfaces and the first, second, third, and fourth interior surfaces may each include teeth. Furthermore, the first and second members and the first and second wedges may cooperate to define at least one aperture through the implant adapted for bone growth therethrough.

[0013] A fifth aspect of the present invention is yet another expandable implant for implantation between two vertebral bodies. In one embodiment of this fifth aspect, the implant includes a first member, the first member including a first vertebral contact surface and a first interior surface having a first and third angled interior surfaces, a second member, the second member including a second vertebral contact surface and a second interior surface having second and fourth angled interior surfaces, the first and second interior surfaces facing towards one another, a plurality of struts attached to both the first and second members, a first wedge disposed between the first and second interior surfaces, the first wedge including first and second angled wedge surfaces for cooperating with the first and second angled interior surfaces of the first and second members respectively, a first tether connecting the first wedge to one of the first or second members, a second wedge disposed between the first and second interior surfaces, the second wedge including third and fourth angled wedge surfaces for cooperating with the third and fourth angled interior surface of the first and second members respectively, and a first tether connecting the first wedge to one of the first or second members. Preferably, in this embodiment, movement of the first wedge towards the second wedge causes an increase in a distance between the first and second interior surfaces, and the first, second, third, and fourth wedge surfaces and the first, second, third, and fourth interior surfaces each include teeth. In another embodiment, one of the first or second wedges may include a bulleted or rounded surface for aiding in insertion of the expandable implant between the two vertebral bodies.

[0014] A sixth aspect of the present invention is a method of implanting an expandable implant between two vertebral bodies. In a first embodiment of this sixth aspect, the method includes the steps of inserting the expandable implant between two vertebral bodies, the implant having a first member, a second member, and a wedge disposed between the first and second members and attached to at least one of the first or second members. The method also includes the step of moving the wedge in a first direction so as to cause movement of the first and second members in a second direction. Preferably, the moving step causes expansion of the first and second members which in turn causes movement of the vertebral bodies away from one another.

[0015] In other embodiments of the sixth aspect, the moving step may be performed through the use of a deployment tool. The inserting step may also be performed through the use of the deployment tool. In certain embodiments, the implant may further include at least one deformable strut and more than one wedge. Each wedge may be attached to at least one of the first or second members by a deformable tether, or in some cases, the wedges may be attached to both members by deformable tethers. Additionally, the implant may further include structure which allows for the movement of the at least one wedge in a first direction, but prevents movement of the wedge in an opposition direction. Furthermore, the wedge may be prevented from torsionally rotating with respect to the first and second members.

[0037] Referring to the drawings, wherein like reference numerals refer to like elements, FIGS. 1-6 depict a first embodiment expandable intervertebral implant, designated generally by reference numeral 10. As is shown in the drawings, implant 10 includes, among other elements that will be discussed below, a first member 12, a second member 14, a first wedge 16, a second wedge 18, and a plurality of struts 20a-d. Implant 10 is designed so that is capable of expanding from a generally unexpanded state (shown in FIGS. 1-5) to a fully expanded state (shown in FIG. 6), as well as several different partial expended states therebetween. The specific details of the structure and the operation of implant 10 will be discussed further below.

[0038] As is shown in FIGS. 1-6, first and second members 12 and 14 are generally planar plate-like elements capable of contacting and supporting a portion of vertebral bodies implant 10 is inserted between. First member 12 includes a first vertebral body contacting surface 22 and a first interior surface 24 having two first angled interior surfaces 26a and 26b. Likewise, second member includes a second vertebral body contacting surface 28 and a second interior surface 30 having two second angled interior surfaces 32a and 32b. First and second vertebral body contacting surfaces 22 and 28 may include bone engaging elements. For example, as is shown in FIGS. 1-6, first vertebral body contacting surface 22 includes projections 23 and second vertebral body contacting surface 28 includes projections 29. Preferably, these projections are capable of biting into a portion of the bone of the adjacent vertebral bodies implant 10 is inserted between. Furthermore, first angled interior surfaces 26a and 26b may include teeth 27a and 27b, respectively, while second angled interior surfaces 32a and 32b may include teeth 33a and 33b, respectively. Finally, first member 12 may define a first aperture 34 and second member 14 may define a second aperture 35 (only partially shown).

[0039] As is also shown in FIGS. 1-6, first and second wedges 16 and 18 are somewhat triangular and include surfaces capable of cooperating with the above-discussed first and second angled interior surfaces. Specifically, first wedge 16 includes first and second angled wedge surfaces 36a and 36b for cooperation with first angled interior surface 26a and second angled interior surface 32a, and second wedge 18 includes third and fourth angled wedge surfaces 38a and 38b for cooperation with first angled interior surface 26b and second angled interior surface 32b. The various wedge surfaces may include similar teeth to those discussed above in connection with first and second angled interior surfaces. For instance, as is best shown in FIG. 5, first and second angled wedge surfaces 36a and 36b include teeth 37a and 37b, respectively, and third and fourth angled wedges surfaces 38a and 38b include teeth 39a and 39b, respectively. The different cooperating teeth (i.e., 27a and 37a, 27b and 39a, 33a and 37b, and 33b and 39b) preferably allow for movement of first and second wedges 16 and 18 with respect to first and second members 12 and 14 in one direction, but prevent it in an opposite direction. This will be discussed further below. It is to be understood that the wedges may exhibit any shape suitable for use in expansion of implant 10.

[0040] First wedge 16 may further include an angled, bulleted, or rounded exterior surface for aiding in insertion of implant 10 between adjacent vertebrae. In the embodiment shown in FIGS. 1-6, first wedge 16 includes rounded exterior surfaces 40a-d, which provides the bulleted nature of the exterior to the element. However, it is to be understood that angled surfaces may also be employed to achieve essentially the same functionality. First wedge 16 also preferably includes a first wedge aperture 42 (best shown in FIG. 1) formed therethrough and second wedge 18 preferably includes a second wedge aperture 44 (best shown in FIG. 2) formed therethrough. Both of these additional elements are preferably provided for use during expansion of implant 10, as will be discussed further below.

[0041] Struts 20a-d are preferably deformable so as to allow for the expansion of implant 10 upon the movement of first and second members 12 and 14 away from one another. There are many different designs for such deformable struts that may be employed. For example, as is shown in FIGS. 1-6, struts 20a-d are of an s-curve shape which facilitate easy compression and expansion. In addition, struts 20a-d are preferably designed so that they apply tension to first and second members 12 and 14 during and after expansion of implant 10. This encourages even deployment of the device. More particularly, each of struts 20a-20d incorporates a specific structure designed to aid in the movement in first and second members 12 and 14 away from one another. As is shown in FIG. 5, each of the struts (of which only struts 20a and 20b are shown in FIG. 5) includes at least one curved section 102, which is designed to be thicker than at least one middle section 104, such that the curved section 102 will deform subsequent to the deformation of middle section 104. Furthermore, each strut preferably includes at least one end section 106 that is joined to one of end plates 12 and 14. This end section 106 is preferably designed in a thicker fashion, such that there is no deformation at this point at anytime during the entire expansion sequence. Thus, the specific configuration of struts 20a-d facilitates the even deployment of implant 10 by specifically providing a structure that allows for a predetermined and consistent expansion sequence.

[0042] First and second wedges 16 and 18 are each respectively attached to both first and second members 12 and 14. As is shown in FIGS. 1-6, first wedge 16 is attached to first member 12 through the use of tethers 46a and 46b, and to second member 14 through the use of tethers 46c and 46d. Likewise, second wedge 18 is attached to first member 12 through the use of tethers 48a and 48b, and to second member 14 through the use of tethers 48c and 48d. Of course, any number of tethers may be utilized in connecting the wedges to the first and second members. Tethers 46a-d and 48a-d are preferably deformable so as to allow the movement of first and second wedges 16 and 18 with respect to first and second members 12 and 14. As is shown in the figures, the tethers may employ a shape that allows them to deform in a proper fashion upon movement of first and second wedges 16 and 18 with respect to first and second members 12 and 14. Like struts 20a-d, tethers 46a-d and 48a-d incorporate a structure specifically designed to allow for an even and consistent deployment of implant 10. Specifically, each tether includes an end section 110 (best shown in connection with the illustration of tethers 46a, 46c, 48a, and 48c in FIG. 5) at the connection between the tether and one of first or second members 12 or 14, which is thicker than other areas of the tether to limit deformation. In addition, this section 110 is shaped in the manner shown in order to force a thinner curved tether section 112 to deform toward either the first or second member during the initial expansion of implant 10. This specific geometry results in the tether's initial movement to be a collapsing motion at section 110. Furthermore, each of tethers 46a-d and 48a-d include a connection section 114 at the connection between the tether and one of first or second wedges 16 or 18. This section, like section 110, is thicker than section 112 to limit the amount of deformation at the coupling of the tether and the wedge. The final expanded state of implant 10 is best shown in FIG. 6, which illustrates the final position of the tethers.

[0043] In order to be suitable for implantation into the human body, all of the elements of implant 10 are preferably biocompatible. For example, in a preferred embodiment, each of the components of implant 10 is constructed of a metal, such as titanium (commercially pure grade 2). However, other biocompatible materials may be utilized, like other titaniums, PEEK, titanium/PEEK composites, nitonol, bioresorbables, and the like. Depending upon the material utilized, certain of the components may be formed integral with or separately from one another. For example, struts 20a-d, in certain embodiments, may be formed integral with first and second members 12 and 14. Of course, in other embodiments, struts 20a-d and first and second members 12 and 14 may be formed separately and constructed together in accordance with normal practices. For instance, these portions could be welded or otherwise fused together.

[0044] Implant 10 also preferably includes certain elements which cooperate to substantially prevent torsional movement of the first and second wedges 16 and 18 with respect to first and second members 12 and 14. Of course, such elements are not required for proper operation of the device. As is shown in FIGS. 1-6, first and second members 12 and 14 are provided with elongate protuberances (50a-d and 52a-d, respectively). These protuberances preferably extend somewhat below the angled interior surfaces of first and second members 12 and 14, respectively. First and second wedges 16 and 18, on the other hand, each include four channels for cooperation with the protuberances. Specifically, first wedge includes channels 54a-d and second wedge includes channels 56a-d.

[0045] The cooperation between the above-discussed protuberances and channels is such that movement of wedges 16 and 18 with respect to each other and first and second members 12 and 14 is not inhibited (i.e., the wedges can move in similar directions as depicted by arrows A and B of FIG. 5). However, any torsional or rotational movement of the wedges with respect to the first and second members is prevented. In other words, first and second wedges 16 and 18 are prevented from going off track. This is an important feature in ensuring a consistent operation of implant 10.

[0046] In operation, movement of first wedge 16 in the direction of arrow A (FIG. 5) and movement of second wedge 18 in the direction of arrow B (also FIG. 5), causes first and second members 12 and 14 to move away from one another. In other words, movement of first and second wedges 16 and 18 towards one another causes the expansion of implant 10. Movement of first and second wedges 16 and 18 can be achieved through the use of a deployment tool (discussed below). At least a portion of such a tool preferably passes through second wedge aperture 44 of second wedge 18, through an interior of implant 10 defined by first and second members 12 and 14 and struts 20a-d, and into engagement with first wedge aperture 42. In certain embodiments, first wedge aperture 42 is threaded so as to allow for threadable engagement of the tool to the first wedge. However, other connections may also be utilized. As is discussed more fully below, deployment tool preferably acts so as to apply a pushing force to second wedge 18 while at the same time applying a pulling force to first wedge 16. This causes the necessary movement of the first and second wedges 16 and 18 towards one another.

[0047] The deformable nature of tethers 46a-d and 48a-d allows them to follow along with first and second wedges 16 and 18 during their movement towards one another. So, at all times the wedges are connected to first and second members 12 and 14, thereby preventing them from becoming dislodged from implant 10. This is an important safety feature of the implant. Furthermore, the above-discussed teeth located on the first and second angled interior surfaces and the angled wedge surfaces allows for the movement of first and second wedges 16 and 18 in the direction of arrows A and B, respectively, but prevents opposite movement of the components. In other words, the different cooperating teeth (i.e., 27a and 37a, 27b and 39a, 33a and 37b, and 33b and 39b) are designed so as to allow the first movement, but prevent the second, opposite movement. Many different teeth designs can be employed in order to achieve this functionality.

[0048] FIGS. 13-19 depict an impaction instrument 310. This instrument is preferably utilized by a surgeon or other medical professional in order to initially place the implant between two adjacent vertebral bodies. Because of the nature of a damaged intervertebral disc space (i.e., in a collapsed position), even the nonexpanded state of implant 10 may be slightly larger than the space between adjacent vertebral bodies. Thus, an impaction instrument, like instrument 310, often must be utilized in initially placing implant 10 in position. As is shown in FIGS. 13-19, instrument 310 includes three separate components, a tapered rod 312, a sleeve 314, and a locking knob 316. Tapered rod 312 is preferably threaded at its distal end 318 in order to couple with a portion of implant 10. In other embodiments, different coupling mechanisms may be employed. Sleeve 314 preferably includes a pair of deformable fingers 320a and 320b, which are capable of expanding outwardly upon insertion of sleeve 314 over the tapered portion 322 of tapered rod 312. This expanded state is best shown in FIGS. 13-15.

[0049] In use of instrument 310, a surgeon would first couple tapered rod 312 with implant 10, by passing distal end 318 of the rod through aperture 44 in the wedge 18 and into contact with aperture 42 of first wedge 16. At this time, the threadable connection can be made by simply threading distal portion into aperture 42. The general coupling of rod 312 with implant 10 is best shown in FIG. 16, while FIG. 18 depicts the threadable coupling of the distal end of rod 312 with aperture 42 of first wedge 16. Once the position shown in FIG. 16 is achieved, a surgeon or other medical professional then preferably slides sleeve 314 over tapered rod 12, thereby expanding fingers 320a and 320b. This state is best shown in FIG. 17. As is shown in the cross sectional view of FIG. 18, fingers 320a and 320b contact a portion of each of first and second members 12 and 14. In addition, as sleeve rod 314 is inserted over tapered rod 312, a shoulder portion 324 of such is engaged with an exterior portion of second wedge 18. At the same time, distal end 318 of rod 312 is engaged with aperture 42 of wedge 16 and a shoulder portion 325 of rod 312 is in contact with a surface of wedge 16. In this position, locking knob 316 is then tightened down on the proximal end 326 of instrument 310, thereby locking rod 312 and sleeve 314 in position. Implant 10 is now protected for insertion through impaction, as first and second members 12 and 14, and wedges 16 and 18 are locked in position and cannot move with respect to each other or any other component of this assembly. A hammer or other impaction instrument can be utilized to apply a force to a back portion 328 (best shown in FIG. 19) of locking knob 316 in order to push implant 10 into the intervertebral disc space. In this regard, it is to be understood that portion 328 may be provided with a coating or other material suitable to accept the shock provided by the force from a hammer or the like.

[0050] FIG. 20 shows a sample deployment tool 350. As is mentioned above, such tool includes a distal portion 352 (shown being disposed within implant 10) capable of passing through aperture 44 of second wedge 18 and into engagement with aperture 42 of first wedge 16. In addition, tool 350 also includes a portion 354 capable of engagement with second wedge 18. Upon actuation of a trigger 356, first portion 352 and second portion 354 move toward one another, thereby pushing wedges 16 and 18 toward one another. This movement of first and second portion 352 and 354 towards one another is facilitated by an actuation mechanism 358 associated with trigger 356. As is more fully discussed above, this movement leads to the expansion of implant 10. Although the embodiment shown includes a first portion, which is designed to threadably connect with aperture 42, other connections are clearly contemplated.

[0051] During a surgical procedure, a surgeon would preferably insert an unexpanded implant 10 into the space between two adjacent vertebra, utilizing the above-discussed impaction instrument 310. This space would preferably first be cleared so as to provide the space necessary to receive the implant. The angled, bulleted, or rounded exterior surface of first wedge 16 is preferably first inserted thereby aiding in the complete insertion of implant 10. These surfaces essentially make insertion easier, and may facilitate a slight distraction of the adjacent vertebra in order to allow for acceptance of implant 10 into the space. Impaction instrument 310 preferably holds the various components of implant 10 in a locked position throughout the insertion. Once fully inserted between the adjacent vertebrae, deployment tool 350 may be engaged with implant 10. It is to be understood that while insertion and deployments of the implant can be achieved through the use of two different tools, it is also possible to utilize a single tool for both steps. For example, a combination impaction and deployment tool (not shown) could be provided and engaged with implant 10 prior to insertion and left attached throughout deployment.

[0052] Upon movement of first and second wedges 16 and 18 towards one another, first and second members 12 and 14 expand, which preferably acts to both distract the vertebral space and also dig projections 23 and 29 of the vertebral contact surfaces 22 and 28 into the vertebral end plates of the vertebra they are in contact with. As is mentioned above, the different cooperating teeth (i.e., 27a and 37a, 27b and 39a, 33a and 37b, and 33b and 39b) allow for the expansion of implant 10, but prevent its contraction. Thus, once expanded, implant 10 remains in such a state without the addition of any further components. Nonetheless, one or more locking components could be utilized to ensure that implant 10 remains in the expanded state.

[0053] It is to be understood that the above brief discussion of the surgical procedure associated with the present invention is merely exemplary, and more, less, or different steps may be performed. Moreover, it is to be understood that more than one implant 10 may be inserted and deployed between adjacent vertebrae. Depending upon the overall size of the implant (which may widely vary), more than one implant may be required in order to properly support the disc space. With the implant(s) in place and deployed, the disc space is preferably restored to at or near its original height. Bone growth may preferably occur through apertures 34 and 36 of the first and second members 12 and 14, respectively. It is noted that first and second wedges 12 and 14 may include similar apertures or voids which ensure an open passage through implant 10 upon full expansion. In the expanded state, the interior of implant 10 can be packed with bone morphonogenic proteins or other bone growth inducing substances in order to encourage this bone growth from one adjacent vertebra to the other.

[0054] FIGS. 7-9 depict a second embodiment implant 110. Essentially, implant 110 is substantially similar to implant 10 save for the inclusion of different torsion inhibiting elements. Because of the similarity of implant 110 with implant 10, similar or identical elements will be referred to with like reference numerals within the 100-series of numbers. For example, implant 110 includes first and second members 112 and 114 which are expandable upon movement of first and second wedges 114 and 116 towards one another. However, in the embodiment shown in FIGS. 7-9, first and second members 112 and 114 are provided with apertures (150a-d and 152a-d, respectively) which are capable of receiving protuberances (not shown). For example, these apertures may receive pins, screws, or plugs which extend somewhat below the angled interior surfaces of first and second members 112 and 114, respectively. First and second wedges 116 and 118, on the other hand, each include four channels for cooperation with the protuberances. Specifically, first wedge includes channels 154a-d and second wedge includes channels 156a-d.

[0055] The cooperation between the protuberances and channels is like that that similar elements of implant 10 such that movement of wedges 116 and 118 with respect to each other and first and second members 112 and 114 is not inhibited. However, any torsional or rotational movement of the wedges with respect to the first and second members is prevented. In other words, first and second wedges 116 and 118 are prevented from going off track.

[0056] FIGS. 10-12 depict yet another embodiment implant 210. Like, implant 110, implant 210 is similar to implant 10, save for the inclusion of different torsion inhibiting elements. Once again, like elements in implant 210 will be referred to within the 200-series of numbers. Instead of including a series of channels and protuberances, the torsion inhibiting elements of implant 210 include a tongue and groove cooperation between its first and second members 212 and 214 and its first and second wedges 216 and 218. Specifically, first wedge 216 is provided with a first tongue 250a for cooperation with a first groove 252a of the first member, and a second tongue 250b for cooperation with a second groove 252b of the first member. Likewise, second wedge 218 is provided with a first tongue 250c for cooperation with a first groove 252c of the first member, and a second tongue 250d for cooperation with a second groove 252d of the second member. These elements cooperate in order to provide a nearly identical function to that of the torsion inhibiting elements discussed above in connection with implant 110. It is to be understood that each of the above discussed torsion inhibiting elements may vary. For instance, the specific shapes of the elements can widely vary. Moreover, the inclusion of certain elements on certain components may be swapped. For example, implant 210 may include wedges employing grooves and first and second members employing tongues.

[0057] Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.