Tool for implanting expandable intervertebral implant

An expandable intervertebral implant and tool for use in implanting same are disclosed. The tool is useful in retaining the implant in a non-expanded state throughout insert of the implant between adjacent vertebral bodies. Among other elements, the tool includes a rod, a sleeve placed over the rod, and a locking knob attached to the rod and the sleeve to fix them with respect to each other. This construct preferably aids in preventing movement of the various components of the implant, including first and second members and first and second wedges. A method of attaching inserting the implant through the use of the tool and attaching the tool to the implant are also disclosed.

BACKGROUND OF THE INVENTION

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.

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.

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.

SUMMARY OF THE INVENTION

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

DETAILED DESCRIPTION

Referring to the drawings, wherein like reference numerals refer to like elements,FIGS. 1-6depict a first embodiment expandable intervertebral implant, designated generally by reference numeral10. As is shown in the drawings, implant10includes, among other elements that will be discussed below, a first member12, a second member14, a first wedge16, a second wedge18, and a plurality of struts20a-d. Implant10is designed so that is capable of expanding from a generally unexpanded state (shown inFIGS. 1-5) to a fully expanded state (shown inFIG. 6), as well as several different partial expended states therebetween. The specific details of the structure and the operation of implant10will be discussed further below.

As is shown inFIGS. 1-6, first and second members12and14are generally planar plate-like elements capable of contacting and supporting a portion of vertebral bodies implant10is inserted between. First member12includes a first vertebral body contacting surface22and a first interior surface24having two first angled interior surfaces26aand26b. Likewise, second member includes a second vertebral body contacting surface28and a second interior surface30having two second angled interior surfaces32aand32b. First and second vertebral body contacting surfaces22and28may include bone engaging elements. For example, as is shown inFIGS. 1-6, first vertebral body contacting surface22includes projections23and second vertebral body contacting surface28includes projections29. Preferably, these projections are capable of biting into a portion of the bone of the adjacent vertebral bodies implant10is inserted between. Furthermore, first angled interior surfaces26aand26bmay include teeth27aand27b, respectively, while second angled interior surfaces32aand32bmay include teeth33aand33b, respectively. Finally, first member12may define a first aperture34and second member14may define a second aperture35(only partially shown).

As is also shown inFIGS. 1-6, first and second wedges16and18are somewhat triangular and include surfaces capable of cooperating with the above-discussed first and second angled interior surfaces. Specifically, first wedge16includes first and second angled wedge surfaces36aand36bfor cooperation with first angled interior surface26aand second angled interior surface32a, and second wedge18includes third and fourth angled wedge surfaces38aand38bfor cooperation with first angled interior surface26band second angled interior surface32b. 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 inFIGS. 5, first and second angled wedge surfaces36aand36binclude teeth37aand37b, respectively, and third and fourth angled wedges surfaces38aand38binclude teeth39aand39b, respectively. The different cooperating teeth (i.e.,27aand37a,27band39a,33aand37b, and33band39b) preferably allow for movement of first and second wedges16and18with respect to first and second members12and14in 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 implant10.

First wedge16may further include an angled, bulleted, or rounded exterior surface for aiding in insertion of implant10between adjacent vertebrae. In the embodiment shown inFIGS. 1-6, first wedge16includes rounded exterior surfaces40a-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 wedge16also preferably includes a first wedge aperture42(best shown inFIG. 1) formed therethrough and second wedge18preferably includes a second wedge aperture44(best shown inFIG. 2) formed therethrough. Both of these additional elements are preferably provided for use during expansion of implant10, as will be discussed further below.

Struts20a-dare preferably deformable so as to allow for the expansion of implant10upon the movement of first and second members12and14away from one another. There are many different designs for such deformable struts that may be employed. For example, as is shown inFIGS. 1-6, struts20a-dare of an s-curve shape which facilitate easy compression and expansion. In addition, struts20a-dare preferably designed so that they apply tension to first and second members12and14during and after expansion of implant10. This encourages even deployment of the device. More particularly, each of struts20a-20dincorporates a specific structure designed to aid in the movement in first and second members12and14away from one another. As is shown inFIG. 5, each of the struts (of which only struts20aand20bare shown inFIG. 5) includes at least one curved section102, which is designed to be thicker than at least one middle section104, such that the curved section102will deform subsequent to the deformation of middle section104. Furthermore, each strut preferably includes at least one end section106that is joined to one of end plates12and14. This end section106is 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 struts20a-dfacilitates the even deployment of implant10by specifically providing a structure that allows for a predetermined and consistent expansion sequence.

First and second wedges16and18are each respectively attached to both first and second members12and14. As is shown inFIGS. 1-6, first wedge16is attached to first member12through the use of tethers46aand46b, and to second member14through the use of tethers46cand46d. Likewise, second wedge18is attached to first member12through the use of tethers48aand48b, and to second member14through the use of tethers48cand48d. Of course, any number of tethers may be utilized in connecting the wedges to the first and second members. Tethers46a-dand48a-dare preferably deformable so as to allow the movement of first and second wedges16and18with respect to first and second members12and14. 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 wedges16and18with respect to first and second members12and14. Like struts20a-d, tethers46a-dand48a-dincorporate a structure specifically designed to allow for an even and consistent deployment of implant10. Specifically, each tether includes an end section110(best shown in connection with the illustration of tethers46a,46c,48a, and48cinFIG. 5) at the connection between the tether and one of first or second members12or14, which is thicker than other areas of the tether to limit deformation. In addition, this section110is shaped in the manner shown in order to force a thinner curved tether section112to deform toward either the first or second member during the initial expansion of implant10. This specific geometry results in the tether's initial movement to be a collapsing motion at section110. Furthermore, each of tethers46a-dand48a-dinclude a connection section114at the connection between the tether and one of first or second wedges16or18. This section, like section110, is thicker than section112to limit the amount of deformation at the coupling of the tether and the wedge. The final expanded state of implant10is best shown inFIG. 6, which illustrates the final position of the tethers.

In order to be suitable for implantation into the human body, all of the elements of implant10are preferably biocompatible. For example, in a preferred embodiment, each of the components of implant10is 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, struts20a-d, in certain embodiments, may be formed integral with first and second members12and14. Of course, in other embodiments, struts20a-dand first and second members12and14may be formed separately and constructed together in accordance with normal practices. For instance, these portions could be welded or otherwise fused together.

Implant10also preferably includes certain elements which cooperate to substantially prevent torsional movement of the first and second wedges16and18with respect to first and second members12and14. Of course, such elements are not required for proper operation of the device. As is shown inFIGS. 1-6, first and second members12and14are provided with elongate protuberances (50a-dand52a-d, respectively). These protuberances preferably extend somewhat below the angled interior surfaces of first and second members12and14, respectively. First and second wedges16and18, on the other hand, each include four channels for cooperation with the protuberances. Specifically, first wedge includes channels54a-dand second wedge includes channels56a-d.

The cooperation between the above-discussed protuberances and channels is such that movement of wedges16and18with respect to each other and first and second members12and14is not inhibited (i.e., the wedges can move in similar directions as depicted by arrows A and B ofFIG. 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 wedges16and18are prevented from going off track. This is an important feature in ensuring a consistent operation of implant10.

In operation, movement of first wedge16in the direction of arrow A (FIG. 5) and movement of second wedge18in the direction of arrow B (alsoFIG. 5), causes first and second members12and14to move away from one another. In other words, movement of first and second wedges16and18towards one another causes the expansion of implant10. Movement of first and second wedges16and18can be achieved through the use of a deployment tool (discussed below). At least a portion of such a tool preferably passes through second wedge aperture44of second wedge18, through an interior of implant10defined by first and second members12and14and struts20a-d, and into engagement with first wedge aperture42. In certain embodiments, first wedge aperture42is 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 wedge18while at the same time applying a pulling force to first wedge16. This causes the necessary movement of the first and second wedges16and18towards one another.

The deformable nature of tethers46a-dand48a-dallows them to follow along with first and second wedges16and18during their movement towards one another. So, at all times the wedges are connected to first and second members12and14, thereby preventing them from becoming dislodged from implant10. 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 wedges16and18in the direction of arrows A and B, respectively, but prevents opposite movement of the components. In other words, the different cooperating teeth (i.e.,27aand37a,27band39a,33aand37b, and33band39b) 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.

FIGS. 13-19depict an impaction instrument310. 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 implant10may be slightly larger than the space between adjacent vertebral bodies. Thus, an impaction instrument, like instrument310, often must be utilized in initially placing implant10in position. As is shown inFIGS. 13-19, instrument310includes three separate components, a tapered rod312, a sleeve314, and a locking knob316. Tapered rod312is preferably threaded at its distal end318in order to couple with a portion of implant10. In other embodiments, different coupling mechanisms may be employed. Sleeve314preferably includes a pair of deformable fingers320aand320b, which are capable of expanding outwardly upon insertion of sleeve314over the tapered portion322of tapered rod312. This expanded state is best shown inFIGS. 13-15.

In use of instrument310, a surgeon would first couple tapered rod312with implant10, by passing distal end318of the rod through aperture44in the wedge18and into contact with aperture42of first wedge16. At this time, the threadable connection can be made by simply threading distal portion into aperture42. The general coupling of rod312with implant10is best shown inFIG. 16, whileFIG. 18depicts the threadable coupling of the distal end of rod312with aperture42of first wedge16. Once the position shown inFIG. 16is achieved, a surgeon or other medical professional then preferably slides sleeve314over tapered rod12, thereby expanding fingers320aand320b. This state is best shown inFIG. 17. As is shown in the cross sectional view ofFIG. 18, fingers320aand320bcontact a portion of each of first and second members12and14. In addition, as sleeve rod314is inserted over tapered rod312, a shoulder portion324of such is engaged with an exterior portion of second wedge18. At the same time, distal end318of rod312is engaged with aperture42of wedge16and a shoulder portion325of rod312is in contact with a surface of wedge16. In this position, locking knob316is then tightened down on the proximal end326of instrument310, thereby locking rod312and sleeve314in position. Implant10is now protected for insertion through impaction, as first and second members12and14, and wedges16and18are 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 portion328(best shown inFIG. 19) of locking knob316in order to push implant10into the intervertebral disc space. In this regard, it is to be understood that portion328may be provided with a coating or other material suitable to accept the shock provided by the force from a hammer or the like.

FIG. 20shows a sample deployment tool350. As is mentioned above, such tool includes a distal portion352(shown being disposed within implant10) capable of passing through aperture44of second wedge18and into engagement with aperture42of first wedge16. In addition, tool350also includes a portion354capable of engagement with second wedge18. Upon actuation of a trigger356, first portion352and second portion354move toward one another, thereby pushing wedges16and18toward one another. This movement of first and second portion352and354towards one another is facilitated by an actuation mechanism358associated with trigger356. As is more fully discussed above, this movement leads to the expansion of implant10. Although the embodiment shown includes a first portion, which is designed to threadably connect with aperture42, other connections are clearly contemplated.

During a surgical procedure, a surgeon would preferably insert an unexpanded implant10into the space between two adjacent vertebra, utilizing the above-discussed impaction instrument310. 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 wedge16is preferably first inserted thereby aiding in the complete insertion of implant10. These surfaces essentially make insertion easier, and may facilitate a slight distraction of the adjacent vertebra in order to allow for acceptance of implant10into the space. Impaction instrument310preferably holds the various components of implant10in a locked position throughout the insertion. Once fully inserted between the adjacent vertebrae, deployment tool350may be engaged with implant10. 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 implant10prior to insertion and left attached throughout deployment.

Upon movement of first and second wedges16and18towards one another, first and second members12and14expand, which preferably acts to both distract the vertebral space and also dig projections23and29of the vertebral contact surfaces22and28into the vertebral end plates of the vertebra they are in contact with. As is mentioned above, the different cooperating teeth (i.e.,27aand37a,27band39a,33aand37b, and33band39b) allow for the expansion of implant10, but prevent its contraction. Thus, once expanded, implant10remains in such a state without the addition of any further components. Nonetheless, one or more locking components could be utilized to ensure that implant10remains in the expanded state.

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 implant10may 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 apertures34and36of the first and second members12and14, respectively. It is noted that first and second wedges12and14may include similar apertures or voids which ensure an open passage through implant10upon full expansion. In the expanded state, the interior of implant10can 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.

FIGS. 7-9depict a second embodiment implant110. Essentially, implant110is substantially similar to implant10save for the inclusion of different torsion inhibiting elements. Because of the similarity of implant110with implant10, similar or identical elements will be referred to with like reference numerals within the 100-series of numbers. For example, implant110includes first and second members112and114which are expandable upon movement of first and second wedges114and116towards one another. However, in the embodiment shown inFIGS. 7-9, first and second members112and114are provided with apertures (150a-dand152a-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 members112and114, respectively. First and second wedges116and118, on the other hand, each include four channels for cooperation with the protuberances. Specifically, first wedge includes channels154a-dand second wedge includes channels156a-d.

The cooperation between the protuberances and channels is like that that similar elements of implant10such that movement of wedges116and118with respect to each other and first and second members112and114is 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 wedges116and118are prevented from going off track.

FIGS. 10-12depict yet another embodiment implant210. Like, implant110, implant210is similar to implant10, save for the inclusion of different torsion inhibiting elements. Once again, like elements in implant210will be referred to within the 200-series of numbers. Instead of including a series of channels and protuberances, the torsion inhibiting elements of implant210include a tongue and groove cooperation between its first and second members212and214and its first and second wedges216and218. Specifically, first wedge216is provided with a first tongue250afor cooperation with a first groove252aof the first member, and a second tongue250bfor cooperation with a second groove252bof the first member. Likewise, second wedge218is provided with a first tongue250cfor cooperation with a first groove252cof the first member, and a second tongue250dfor cooperation with a second groove252dof 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 implant110. 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, implant210may include wedges employing grooves and first and second members employing tongues.