Method and apparatus for spinal facet fusion

A spinal facet fusion implant includes an elongated main body having a distal end, a proximal end and a longitudinal axis extending between the distal end and the proximal end. The main body has a cross-sectional profile characterized by a primary axis and a secondary axis. At least one stabilizer extends radially outwardly from the main body in the secondary axis. The main body has a length along the primary axis that is less than the combined width of the spinal facets making up a facet joint. The stabilizer has a width that is sized to make a press fit into the gap between the spinal facets making up a facet joint.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to surgical methods and apparatus in general, and more particularly to surgical methods and apparatus for fusing spinal facets.

2. Description of the Related Art

Disc herniation is a condition where a spinal disc bulges from between two vertebral bodies and impinges on adjacent nerves, thereby causing pain. The current standard of care for surgically treating disc herniation in patients who have chronic pain and who have (or are likely to develop) associated spinal instability is spinal fixation. Spinal fixation procedures are intended to relieve the impingement on the nerves by removing the portion of the disc and/or bone responsible for compressing the neural structures and destabilizing the spine. The excised disc or bone is replaced with one or more intervertebral implants, or spacers, placed between the adjacent vertebral bodies.

In some cases, the spinal fixation leaves the affected spinal segment unstable. In this case, the spinal facets (i.e., the bony fins extending upwardly and downwardly from the rear of each vertebral body) can disengage with one another. The disengagement of the spinal facets can cause substantial pain to the patient. Furthermore, when left untreated, such disengagement of the spinal facets can result in the degeneration of the cartilage located between opposing facet surfaces, ultimately resulting in osteoarthritis, which can in turn lead to worsening pain for the patient.

Thus, where the patient suffers from spinal instability, it can be helpful to stabilize the facet joints as well as the vertebral bodies. The facet joints are frequently stabilized by fusing the spinal facets in position relative to one another.

In addition to providing stability, fusing the spinal facets can also be beneficial in other situations as well. By way of example but not limitation, osteoarthritis (a condition involving the degeneration, or wearing away, of the cartilage at the end of bones) frequently occurs in the facet joints. The prescribed treatment for osteoarthritis disorders depends on the location, severity and duration of the disorder. In some cases, non-operative procedures (including bed rest, medication, lifestyle modifications, exercise, physical therapy, chiropractic care and steroid injections) may be satisfactory treatment. However, in other cases, surgical intervention may be necessary. In cases where surgical intervention is prescribed, spinal facet fusion may be desirable.

A minimally-invasive, percutaneous approach for fusing spinal facets was proposed by Stein et al. (“Stein”) in 1993. The Stein approach involved using a conical plug, made from cortical bone and disposed in a hole formed intermediate the spinal facet joint, to facilitate the fusing of opposing facet surfaces. However, the clinical success of this approach was limited. This is believed to be because the Stein approach did not adequately restrict facet motion. In particular, it is believed that movement of Stein's conical plug within its hole permitted unwanted facet movement to occur, thereby undermining facet fusion. Furthermore, the Stein approach also suffered from plug failure and plug migration.

Thus there is a need for a new and improved approach for effecting spinal facet fusion.

However, in view of the art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the field of this invention how the shortcomings of the prior art could be overcome.

SUMMARY OF THE INVENTION

The long-standing but heretofore unfulfilled need for improved devices and methods for effecting spinal facet fusion is now met by a new, useful, and nonobvious invention.

The novel method and apparatus for effecting spinal facet fusion includes a novel spinal facet fusion implant for disposition between opposing articular surfaces of a facet joint to immobilize the facet joint and facilitate fusion between the opposing facets.

More particularly, in one form of the present invention, there is provided a spinal facet fusion implant that includes an elongated body having a distal end, a proximal end and a longitudinal axis extending between the distal end and the proximal end. The elongated body has a cross-sectional profile characterized by a primary axis and a secondary axis; and at least one stabilizer extends radially outwardly from the elongated body in the secondary axis.

The elongated body has a length along the primary axis that is less than the combined width of the spinal facets making up a facet joint.

The at least one stabilizer has a width which is sized to make a press fit into the gap between the spinal facets making up a facet joint.

A method for fusing a spinal facet joint includes the steps of providing a spinal facet fusion implant having an elongated body having a distal end, a proximal end and a longitudinal axis extending between the distal end and the proximal end. The method further includes the steps of providing the elongated body with a cross-sectional profile characterized by a primary axis and a secondary axis and providing at least one stabilizer that extends radially outwardly from the elongated body in the secondary axis.

The method steps further include the steps of forming the elongated body so that it has a length along the primary axis which is less than the combined width of the spinal facets making up a facet joint and forming the at least one stabilizer so that it has a width which is sized to make a press fit into the gap between the spinal facets making up a facet joint.

Further method steps include the steps of deploying the spinal facet fusion implant in the facet joint so that the elongated body is simultaneously positioned within both of the facets of the facet joint and so that the at least one stabilizer is positioned within the gap between the spinal facets and maintaining the spinal facet fusion implant in such position while fusion occurs.

In another embodiment, a spinal facet fusion implant includes an elongated body having a distal end, a proximal end and a longitudinal axis extending between the distal end and the proximal end, the elongated body having a cross-sectional profile which is characterized by a primary axis and a secondary axis.

The elongated body has a length along the primary axis which is less than the combined width of the spinal facets making up a facet joint and the cross-sectional profile is non-circular.

In yet another embodiment, a method for fusing a spinal facet joint includes the steps of providing a spinal facet fusion implant having an elongated body having a distal end, a proximal end and a longitudinal axis extending between the distal end and the proximal end, the elongated body having a cross-sectional profile which is characterized by a primary axis and a secondary axis and forming the elongated body so that it has a length along the primary axis which is less than the combined width of the spinal facets making up a facet joint and further providing a non-circular cross-sectional profile.

Further steps include deploying the spinal facet fusion implant in the facet joint so that the elongated body is simultaneously positioned within both of the facets of the facet joint and maintaining the spinal facet fusion implant in such position while fusion occurs.

In still another embodiment, a joint fusion implant includes an elongated body having a distal end, a proximal end and a longitudinal axis extending between the distal end and the proximal end, the elongated body having a cross-sectional profile characterized by a primary axis and a secondary axis and at least one stabilizer extending radially outwardly from the elongated body in the secondary axis.

The elongated body has a length along the primary axis which is less than the combined width of the bones making up the joint and the at least one stabilizer has a width which is sized to make a press fit into the gap between the bones making up the joint.

In another embodiment, a method for fusing a joint includes the steps of providing a fusion implant that includes an elongated body having a distal end, a proximal end and a longitudinal axis extending between the distal end and the proximal end, the elongated body having a cross-sectional profile characterized by a primary axis and a secondary axis and at least one stabilizer extending radially outwardly from the elongated body in the secondary axis.

Further steps include forming the elongated body so that it has a length along the primary axis which is less than the combined width of the bones making up the joint and forming the at least one stabilizer so that it has a width which is sized to make a press fit into the gap between the bones making up the joint.

Still further steps include deploying the fusion implant in the joint so that the elongated body is simultaneously positioned within both of the bones of the joint and the at least one stabilizer is positioned within the gap between the bones and maintaining the fusion implant in such position while fusion occurs.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now toFIGS. 1A-C, the novel spinal facet fusion implant is denoted10as a whole. Fusion implant10includes main body12and at least one stabilizer fin14. The illustrated embodiment includes first stabilizer fin14aand second stabilizer fin14b.

Body10is an elongated element having structural integrity. The distal end of main body12and the distal end of stabilizers14a,14bare chamfered as at16to facilitate insertion of fusion implant10into the facet joint as disclosed hereinafter. Body12preferably has a rounded rectangular cross-section, an ovoid cross-section, a laterally-extended cross-section, or some other non-round cross-section to inhibit rotation of main body12about a longitudinal center axis.

Fusion implant10is intended to be inserted into a facet joint using a posterior approach. The posterior approach is familiar to spine surgeons, thereby providing an increased level of comfort for the surgeon, and also minimizing the possibility of damage to the spinal cord during fusion implant insertion.

Stabilizer fins14a,14bare received in a gap located between opposing facet surfaces to prevent rotation of fusion implant10within the facet joint. Stabilizers14ais formed in and extends along the upper surface of main body12and stabilizer14bis formed in and extends along the lower surface of main body12. Stabilizers14a,14bpreferably have a width just slightly larger than the gap between the opposing articular surfaces of a facet joint so that the stabilizers fit snugly therebetween.

The distal end12aof main body12ahas a greater thickness than proximal end12bof said main body, there being transversely disposed step12ctherebetween. The greater thickness of said distal end supports the load for a long period of time. If said distal end12aof main body12is eventually crushed, it becomes flush with proximal end12band fusion implant10continues to perform its function.

The embodiment ofFIGS. 2A-Chas an inverse taper formed in main body12and in stabilizer fins14a,14bto prevent migration of implant10. As perhaps best understood in connection withFIG. 2B, fin14ais wider at its distal end than at its proximal end; fin14bhas the same structure. This wedge shape prevents distal-to-proximal travel of implant10. This eliminates the need for teeth that perform the same function.

The embodiment ofFIG. 3Adiffers from the embodiment ofFIGS. 2A-Cin that main body12is bulbous on its left and right sides as depicted. It is sometimes referred to as a figure eight main body in view of said bulbosities. The bulbosities are denoted12cand12d. They serve the same function as raised area12ain the embodiment ofFIGS. 1A-Cin that if they are crushed over time until they are flush with the non-bulbous central region of main body12, said main body will still remain firmly and functionally positioned in the facet joint. Without the raised area or the bulbosities, crushing of main body12over time would loosen it relative to its facet joint.

FIGS. 4A-Ddepict an embodiment characterized by main body12that is hexagonal in transverse section as depicted. Stabilizer fins14,14bmay also be shorter in radial extent in this embodiment. This shape helps prevent rotation of implant10.

The embodiment ofFIGS. 5A-Cdiffers from the embodiment ofFIGS. 4A-Din that the embodiment ofFIGS. 5A-Cis not provided with stabilizer fins14a,14b.

The embodiment ofFIGS. 7A-Bhas main body12of polygonal configuration and no stabilizer fins.

Referring now toFIGS. 8A-D, an instrument is first used to determine the vertical plane18of the facet joint. Identifying the vertical plane of the facet joint is important because said plane is used to identify the proper position for cavity20which is to be formed in the facet joint to receive fusion implant10. The superior facet is denoted22ainFIGS. 8-Dand the inferior facet is denoted22b. The inverted tapered cavity depicted inFIGS. 8A-Dis intended for use with the inverted tapered implant ofFIGS. 2A-C.

A disclosure of the novel tools used with implant10follows.

Implant holder26is depicted inFIG. 10. Leading end28includes a plurality of flexible arms28that engage an implant10to lift it from bore24aor24bof implant loading block24. Implant holder26does not have alignment pins. It has flats that align inside directional cannula30. Drill guide36, disclosed hereinafter, also has such flats.

Directional cannula30having diametrically opposed arms30a,30bat its leading or distal end is depicted inFIG. 11. Arms30a,30bmaintain the direction of the joint to guide the other instruments, and also maintain the distraction of the joint.

FIG. 12depicts facet distractor32having leading end32aadapted to engage into the facet joint to find the direction of the plane of the facet joint.

Guide pin34is depicted inFIG. 13. Its use is optional.

FIGS. 14A-Ddepict drill guide36having blade36a, positive stop36b, and alignment flats36c.FIG. 14Ais a first perspective view,FIG. 14Bprovides a side elevational view,FIG. 14Cprovides a top plan view andFIG. 14Dprovides a second perspective view. Drill guide36stabilizes the drill bit during the drilling procedure.

FIGS. 15A-Crespectively depict tapping cap38in perspective, perspective with dotted lines to indicate hidden structure, and in longitudinal section to also reveal hidden structure. Distal bore38aof tapping cap38is used to tap directional cannula30into its functional position and proximal bore38cis used to tap facet distractor32into its functional positional. The diameter of distal bore38areduces down to medial bore38band proximal bore38chas the same diameter as distal bore38a. Medial bore38ballows guide pin34to slide through.

FIGS. 16A and 16Bdepict one step facet distractor32when it is received within the lumen of implant holder40which is a second embodiment of implant holder26.FIG. 16Bdepicts the tip of facet distractor32and implant holder40in enlarged detail. Implant Holder40does not need alignment pins40abecause the orientation is fixed relative to facet distractor32.

FIG. 17depicts implant tamp44that is used to drive a hollow implant10into its functional position. Slots44aallow implant tamp44to slide a predetermined distance as disclosed hereinafter

FIG. 18depicts one step holder46having openings collectively denoted46athat holds the complete instrument assembly while implant10is being tapped into its functional position

The four pins, collectively denoted41inFIG. 16A, are used in the assembly of implant tamp44and handle46. The instrument as assembled includes facet distractor32which is ensleeved within the lumen of implant holder26, which is in turn ensleeved within the lumen of implant tamp44, which is in turn ensleeved within the lumen of handle46. More particularly, pins26aextend sequentially through their associated slots44aand into their associated opening46aformed in handle46.

FIG. 20Ais similar toFIG. 19but it depicts implant10engaged to the distal end of implant holder26.

FIG. 20Bis a longitudinal sectional view of the structure depicted inFIG. 20A.

FIG. 20Dis a longitudinal sectional view of the structure depicted inFIG. 20E;

FIGS. 21A-Cdepict an alternative embodiment of drill guide36depicted inFIGS. 14A-D. This embodiment is denoted48and has blade48a. Two opposed alignment pins50a,50bare formed in drill guide48near handle50. The alignment pins allow insertion into directional cannula30at zero degrees (0°) or one hundred eighty degrees) (180°).

FIG. 22Adepicts a second embodiment, denoted52, of implant tamp44. The shaft of implant tamp52shaft conforms to main body12and said shaft is cannulated as at52ato enable injection of growth stimulation product. The handle of implant tamp52is denoted54.

FIG. 22Bprovides an end view of the structure depicted inFIG. 22A.

A second embodiment of directional cannula30is depicted inFIG. 23and is denoted54. Transversely opposed distraction blades54a,54bare formed in its distal end and handle56is mounted thereto at its proximal end. The transverse cross-sectional shape of directional cannula30matches the transverse cross-sectional shape of implant10.

A second embodiment of facet distractor32is depicted inFIG. 24and is denoted56. It includes blade56aand positive stop56b.

At least one of the instruments includes a directional feature that is used to maintain the alignment of the instrumentation with vertical plane18of the facet joint. By way of example but not limitation, directional cannula30may include a flat portion and the remaining instruments may include a flat portion on an opposite portion of the instrument so that the instruments may only be inserted through said directional cannula at zero degrees (0°) or one hundred eighty degrees)(180°).

After the proper position for cavity20has been identified, a drill (or reamer, punch, dremel, router, burr, etc.) is used to form cavity20in the facet joint. Cavity20is formed across vertical plane18so that substantially one-half of cavity20is formed in a first facet22a, and substantially one-half is formed in opposing facet22b.

After cavity20has been formed in (or, perhaps more literally, across) the facet joint, fusion implant10is inserted into cavity20as perhaps best understood in connection withFIG. 8D. More particularly, fusion implant10is inserted into cavity20so that main body12spans the gap between opposing facets22a,22b, and so that stabilizers14a,14bextend between the opposing facet surfaces. Preferably, fusion implant10is slightly oversized relative to cavity20to create a press fit.

Fusion implant10provides the stability and strength needed to immobilize the facet joint while fusion occurs. Due to the positioning of stabilizers14a,14bbetween the opposing facet surfaces, and due to the non-circular cross-section of main body12, fusion implant10will be held against rotation within cavity20, which will in turn hold facets22a,22bstable relative to one another.

When a hollow fusion implant is used, and where the implant is formed of a sufficiently strong and rigid material, cavity20need not be pre-formed in the opposing facets. The hollow fusion implant can be simply tapped into place, in much the same manner that a punch is used.

The novel structure provides a new and improved fusion implant for facilitating facet fusion. This novel fusion implant withstands greater forces, prohibits motion in all directions and substantially reduces the risk of implant failure. The new fusion implant also eliminates the possibility of slippage during spinal motion, greatly improves facet stability and promotes better facet fusion.

It should be appreciated that the new fusion implant combines two unique “shapes” in one implant (i.e., the shape of main body12and the shape of stabilizers14a,14b) in order to limit motion in a multidirectional joint. More particularly, the shape of main body12limits motion (e.g., in flexion/extension for the lumbar facets and in axial rotation for the cervical facets), while the shape of stabilizers14a,14b(i.e., the “keel”) rests between two bony structures (i.e., in the gap of the facet joint) and limits lateral bending. This novel construction eliminates the possibility of eccentric forces inducing motion in the facet joint.

Moreover, although the novel structure effectively stabilizes the joint, it still allows the “micro motion” which is required for the fusion process to begin.

It should be appreciated that the novel fusion implant may be manufactured in a wide range of different sizes in order to accommodate any size of facet joint. Furthermore, the scale and aspect ratio of main body12, stabilizers14a,14b, may be varied without departing from the scope of the present invention. Additionally, the novel fusion implant may be constructed out of any substantially biocompatible material which has properties consistent with the present invention including, but not limited to, allograft, autograft, synthetic bone, simulated bone material, biocomposites, ceramics, PEEK, stainless steel and titanium. Thus, the novel structure permits a surgeon to select a fusion implant having the appropriate size and composition for a given facet fusion.

Detailed Surgical Technique (Solid Fusion Implant)

A preferred surgical technique for using a solid fusion implant10will now be disclosed. The preferred surgical technique preferably uses guide pin34(FIG. 13) facet distractor32(FIG. 12), directional cannula30(FIG. 11), drill guide36(FIGS. 14A-D), implant loading block24(FIG. 9), implant holder26(FIG. 10) implant tamp44(FIG. 17), and tapping cap38(FIGS. 15A-C).

First, the facet joint is localized indirectly by fluoroscopy, or directly by visualization during an open procedure. Next, guide pin34(FIG. 13) is inserted into the gap between the opposing facet surfaces. The position of guide pin34is verified by viewing the coronal and sagittal planes. Then guide pin34is lightly tapped to insert the guide pin approximately five millimeters (5 mm) into the facet joint, along vertical plane18. The inferior facet is curved medially and helps prevent guide pin34from damaging nerve structures.

Cannulated facet distractor32is then slid over guide pin34so that it is aligned with the vertical plane of the facet joint. Then facet distractor32is lightly tapped into the facet joint, along vertical plane18.

Next, directional cannula30is placed over facet distractor32(FIG. ?) and the tip of directional cannula30is pushed into the facet joint (FIG. ?). Once the tip of directional cannula30has entered the facet joint, the directional cannula is lightly tapped so as to seat the cannula in the facet joint. This aligns directional cannula30with the vertical plane of the facet joint. After verifying that directional cannula30has been inserted all the way into the facet joint and is stabilized in the joint, facet distractor32is removed.

Drill guide36is then inserted into directional cannula30. Drill guide36is advanced within directional cannula30until a drill guide stop is resting on directional cannula30. Then, with drill guide36in place, irrigation (e.g., a few drops of saline) is placed into drill guide. Next, drill bit58is used to drill a cavity20. This is done by drilling until drill bit58reaches the mechanical stop on drill guide36(FIGS. 21A-B). Drill guide36and drill bit58are then pulled out of directional cannula30, drill guide36is rotated 180 degrees, and drill guide36is reinserted into directional cannula30in order to drill the superior facet. With drill guide36in place, irrigation (e.g., a few drops of saline) is placed into said drill guide, and drill bit58is used to drill cavity20in the superior facet. Again, drilling occurs until drill bit58reaches the mechanical stop on drill guide36. Drill bit58is then removed.

Cavity cutter60, depicted inFIG. 26, may replace drill guide36and drill bit58to make an opening having the perfect shape for fusion implant10.

Using implant loading block24depicted inFIG. 9, fusion implant10is then inserted into implant holder26. Implant holder26, with fusion implant10in place, is then placed into directional cannula30. Next, implant holder26is lightly tapped so as to insert fusion implant10into cavity20created in the facet joint. Once the implant has been positioned in cavity20, implant tamp44is inserted into implant holder26. Next, implant tamp44is lightly tapped so as to drive the implant into cavity20. The implant is preferably countersunk 1-2 mm into the facet joint.

Implant tamp44, implant holder26and directional cannula30are removed from the surgical site and the incision is closed to conclude the procedure.

Detailed Surgical Technique (Hollow Fusion Implant)

A preferred surgical technique for using a hollow fusion implant10will now be disclosed. The preferred surgical technique preferably uses guide pin34(optional) (FIG. 13), one step facet distractor and implant holder40(FIG. 16A), implant tamp44(FIG. 17), and handle46(FIG. 17).

First, the facet joint is localized indirectly by fluoroscopy or directly by visualization during an open procedure. The following step involving use of guide pin34is entirely optional. If used, guide pin34is inserted in the gap between the opposing facet surfaces. The position of guide pin34is verified by viewing the coronal and sagittal planes. Guide pin34is then lightly tapped so as to insert said guide pin approximately five millimeters (5 mm) into the facet joint, along the vertical plane of the facet joint. The inferior facet curves medially and helps prevent the guide pin from damaging nerve structures.

One step facet distractor with implant holder40, which may be cannulated or not cannulated, is then slid over guide pin34, if used, so that it is aligned with the vertical plane of the facet joint. Facet distractor32is lightly tapped into the facet joint, along the vertical plane of the facet joint. This step may be accomplished without use of guide pin34.

Next, facet distractor with implant holder40, implant tamp44, handle46assembly, with hollow fusion implant10mounted thereto (FIG. 20A) is pushed, hammered, or otherwise advanced downwards to drive hollow fusion implant10into the facet joint.

Finally, the facet distractor/implant tamp assembly is removed, leaving hollow fusion implant10in the facet joint, and the incision is closed.

The following procedure applies to both solid or hollow implants.

Performing posterior facet fusion with the novel tools is a nine step procedure.

In the first step, the facet joint is localized either indirectly using fluoroscopy or directly by visualization during an open procedure. Facet distractor56is then inserted into the plane of the facet joint. Placement is verified by viewing in the coronal and sagittal plane. The inferior facet curves medially and should prevent guide pin34from being advanced into nerve structures. Tapping cap38is then tapped lightly so that blade56aof facet distractor56aenters into the plane of the facet joint. If necessary, the shallow end38cof the tapping cap can be used to seat the facet distractor. Positive stop56bis formed in facet distractor56to prevent it from being advanced into the nerve structures.

In step three, directional cannula54is placed over facet distractor56. Tip56aof facet distractor56is aligned with tips54a,54bof directional cannula54and is lightly pushed into the facet joint. After tips54a,54bhave entered into the facet joint, directional cannula54is lightly tapped to fully seat it. If necessary, the deep end38aof tapping cap38acan be used to seat the directional cannula.

The insertion of directional cannula54all the way into the facet joint is then verified. Facet distractor56is removed after such positioning is verified.

In step four, drill guide36is inserted into the lumen of directional cannula54, aligning pins50a,50binto slots54a,54bformed in directional cannula54. The insertion continues until drill guide positive stop36babuts directional cannula54and blade48ais in the facet joint.

Step five is the drilling of the inferior facet. With drill guide36in place upon the completion of step four. Cavity20is then drilled by drill bit58into the inferior facet. Drilling continues until drill bit58abuts positive stop58a. Drill guide36is held down when drill bit58is removed and said drill bit is not removed until it has stopped rotating.

Drill guide36and drill bit58are pulled from directional cannula54in step six and it is cleaned to remove tissue. It is then rotated one hundred eighty degrees (180°) and re-inserted into directional cannula30.

Cavity20is drilled into the superior facet in step seven. A few drops of irrigation (saline) are placed into the drill guide. Said cavity is then drilled by drill bit58into the superior facet. Drilling continues until drill bit58abuts positive stop58a. Drill guide36is held down when drill bit58is removed and said drill bit is not removed until it has stopped rotating.

In step eight, an implant is loaded into directional cannula54with the chamfer16pointed downward. Implant tamp52is inserted into the lumen of directional cannula54. Implant tamp52is lightly tapped until it reaches positive stop52bto fully seat implant10in cavity20. Implant tamp52and directional cannula54are then removed.

Numerous advantages are achieved by the present invention. Among other things, the present invention provides a fast, simple, minimally-invasive and easily reproduced approach for effecting facet fusion.

While fusion implant10has been disclosed in the context of fusing a facet joint, it should also be appreciated that fusion implant10may be used to stabilize and fuse any joint having anatomy similar to the facet joint, i.e., a pair of opposing bony surfaces defining a gap therebetween, with the stabilizer of the fusion implant being sized to be positioned within the gap. By way of example but not limitation, the fusion implant may be used in small joints such as the fingers, toes, etc.

Many additional changes in the details, materials, steps and arrangements of parts, which have been herein disclosed in order to explain the nature of the present invention, may be made by those skilled in the art while still remaining within the principles and scope of the invention.