BACKGROUND 1. Technical Field [0002] The present disclosure relates to bone fastener assemblies and, more specifically to a rivet assembly for use in stabilizing facets of adjacent vertebrae to one another. The present disclosure also relates to a fastening tool and, more particularly, to a rivet crimping device for crimping a rivet assembly according to the present disclosure.

In addition, the present disclosure relates to a bone stabilization method and, more particularly to a method for stabilization of adjacent vertebrae to one another using the rivet assembly and rivet crimper according to the present disclosure : 2. Background of Related Art [00031 It is often necessary to fix the facet joints of adjacent vertebrae to one another or to attach objects (e. g. , bone plates, bone grafts, etc. ) to a bone itself. For example, in repairing a fractured or damaged vertebra, it is often necessary to stabilize individual vertebrae in order to promote proper healing. Stabilization is often accomplished by fixing one vertebra to adjacent vertebrae or by using a bone plate, or pedicle screw and rod system, to interconnect adjacent or a series of vertebrae to one another.

10004] Prior art techniques often utilize screws to secure vertebrae or bone to one another or to secure a plate and/or rods between individual vertebrae or between individual bones. In order to more securely anchor a screw into the vertebrae, bicortical placement of the screw into the bone is recommended. In other words, the screw is to penetrate through the cortex layer that is adjacent to the bone plate which is to be attached, then penetrate through the cancellous tissue in the interior of the bone and finally, penetrate into the opposite cortex layer on the opposite side of the bone.

[0005] Entering a bone is an invasive procedure that sometimes, based on the severity of problem which is encountered by an operating surgeon, requires that a screw penetrate through the opposite cortex layers. Accordingly, known screws have an elongated structure capable of bicortical purchase, otherwise the screws may loosen and fail to securely couple the plate to the bone or vertebrae.

[0006] Another known method is the use of pedicle screws for stabilizing adjacent vertebrae as well as for monosegmental or multisegmental fixation of a spinal column.

Such screws typically do not obtain bicortical purchase and are therefore more susceptible to loosening. To help reduce this risk, the longest and largest size screw that can be safely inserted into the dense cancellous bone of the pedicle is used to maximize bone purchase. A typical pedicle screw includes a threaded portion and a receiver portion rigidly connected thereto at the head end of the screw. In use, several pairs of such screws are threaded into the vertebral bodies of the adjacent vertebra on either side of the spinal column through the pedicles. The respective receiver portions comprise receiving slits wherein a respective rod is passed through these receiving slits in the right and left hand group of pedicle screws. Thereafter, the rod is fixed to the respective receiver portion by means of fastening devices.

[0007] It is a drawback of this solution that it is difficult to rigidly insert screws through the pedicles on into the vertebral bodies and at the same time position the pedicle screws in two planes in exactly such a manner that the axes of the receiving slits in the receiver parts in the vertical columns align such that the rod may be passed through the receiving slits without distortion of the screws. Even with the advent of polyaxial screws, alignment of the receiving slits and contouring the rods to fit these slits remain a time consuming process. A further drawback is the difficulty in properly positioning the screws within the pedicles. This takes much skill on the part of the surgeon.

Compromising the integrity of the cortical walls of the pedicle as well as further penetration into the vertebral body of the vertebra could lead to neurological complications and eventual implant loosening. Additionally, the implantation of a pedicle screw system is a very invasive procedure, whereby a large incision is made to expose multiple vertebral levels. This is largely due to the fact that the pedicles of adjacent vertebrae are not themselves directly adjacent, thus the need for the rod to interconnect the pedicle screws inserted into the vertebrae.

[0008] Still another drawback is that the holding power of pedicle screws greatly depends on the length and size of screw used. Increasing the length and size of a screw improves its holding power. However, as discussed above, using such screws that extend through the pedicle on into the vertebral bodies results in a more invasive and time- consuming procedure.

[0009] Furthermore, under normal circumstances, intervertebral discs support approximately 70-80% of axial loads imposed upon the lumbar spine, whereas the rest of such axial loads fall on spinal structures including, among others, the facet joints. As a rule, natural distribution of axial loads is, however, disturbed as a result of implantation surgery. Typically, the pedicle screws carry axial loads in excess of 20-30%. One of the reasons for such a deviation from the natural distribution is the concern that unless the vertebral motion segment to be fused is not adequately immobilized, fusion will not occur. As a result, rigid stabilization systems are necessary for the initial healing. Hence, the pedicle screws, viewed as a structure, which is capable of supporting greater axial loads, are characterized by intentionally massive configurations capable of extending through the vertebral bodies of the adjacent vertebrae. Once fusion has occurred, the extensive pedicle screw hardware is usually left in the patient. There is concern that leaving so much'foreign'material behind could be detrimental to the patient. Finally, there is also a concern that existing pedicle screw systems may in fact be more rigid than necessary for a fusion to occur, and that a less rigid system that allows more'normal' load sharing conditions may be preferable.

[0010] It is, therefore, desirable to provide a simpler, less invasive method of posteriorily stabilizing adjacent vertebra to be fused, as well as an instrumentation system configured to carry out such a method.

SUMMARY OF THE INVENTION [0011] Consonant with the objectives of the present invention, an instrumentation system is configured to fuse the facet joints bridging adjacent superior and inferior vertebrae.

[0012] The function of the facet joint is to guide vertebral motion and to resist compression, rotation and shear forces. Unless traumatized or degenerated, the facet joints offer a strategically advantageous location for receiving supporting structures configured to stabilize adjacent vertebrae to be fused. This is because the facets themselves form a joint, which links adjacent vertebrae.

[0013] In accordance with one aspect of the invention, the inventive instrumentation system includes a rivet assembly shaped and dimensioned to penetrate through a facet joint and thus connect the superior and inferior vertebrae to be fused. The rivet assembly advantageously is configured so as to have its distal end terminate within the base of the superior articular process of the inferior vertebra without further penetration on into the vertebral body thereof.

[0014] Thus, one of the advantages of the inventive rivet assembly is that its structure is more compact and less massive than many of the known structures of bone fasteners in general and, particularly, pedicle screws. Accordingly, the rivet assembly configured in accordance with the invention is less rigid, allowing a more'normal'load sharing condition that may be favorable for fusion.

[0015] In a particular advantageous embodiment of the instrumentation system, the rivet assembly is dimensioned so that when its recessed distal end expands, multiple separate leafs, constituting the distal end, engage the cancellous bone at the base of the superior articular process, and not even its opposite cortex layer, let alone the vertebral body. Thus, the inventive instrumentation system is calibrated to minimally invade a vertebral structure without, however, compromising the stability needed for fusion to occur. Without the need for the device to go all the way through the pedicle, the difficulties associated with the placement of pedicle screws is avoided. Compactness of the inventive rivet assembly allows the vertebral body of the inferior vertebra to remain intact.

[0016] In accordance with another aspect of the invention, the instrumentation system further includes a mandrel driving the distal end of the rivet assembly into engagement with the bone and configured to partially remain within the rivet assembly after its engagement with the bone.

[0017] Configuration of the mandrel includes a weakening portion allowing the body of the rivet to separate into multiple portions, the distal one of which remains rigidly attached within the rivet assembly. To simplify the manufacturing process, the mandrel is advantageously provided with an annular cross-section.

[0018] A further aspect of the invention relates to a rivet crimper specifically configured to engage the mandrel and to apply a pulling force thereto sufficient to pull it apart in a controlled manner, but not before the distal end of the rivet assembly has been driven into the engagement with the inferior vertebra.

[0019] In accordance with another aspect of the invention, a method of stabilizing adjacent vertebrae provides for engagement of the inventive rivet assembly with the inferior vertebrae. One particularly advantageous embodiment of the inventive method includes engagement of the rivet assembly with the cancellous bone at the base of the superior articular process of the inferior vertebrae. Limiting the penetration of the rivet assembly by anchoring its distal end to the base of the superior articular process, represents a considerably less invasive approach than the known methods using pedicle screws which are designed to continue on through the entire length of the pedicle and purchase the structure of the vertebral body. In contrast with pedicle screw systems, which require four screws per fusion level, only two rivet assemblies through the facet joints are needed. The incision required to access this joint is considerably less than that required to access multiple pedicles for placement of a pedicle screw system.

BRIEF DESCRIPTION OF THE DRAWINGS [0020] By way of example only, preferred embodiments of the disclosure will be described with reference to the accompanying drawings, in which: [0021] FIG. 1 is a perspective view of a rivet assembly according to the present disclosure; [0022] FIG. 2 is a side elevational view of the rivet assembly shown in FIG. 1; [0023] FIG. 3 is a perspective view of a rivet body according to the present disclosure; [0024] FIG. 3A is a perspective view of an alternative embodiment of the rivet body; [0025] FIG. 3B is a view of another alternative embodiment of the rivet body; [0026] FIG. 4 is a cross-sectional side elevational view of the rivet body shown in FIG. 3A taken along the longitudinal axis of the rivet assembly; [0027] FIG. 5is an enlarged cross-sectional side elevational view of a distal end of the rivet body shown in FIG. 3 A ; [0028] FIG. 6 is a perspective view of a mandrel according to the present disclosure; [0029] FIG. 7 is an enlarged side elevational view of the mandrel shown in FIG. 6; [0030] FIG. 7A is a sectional view of the rivet assembly in accordance with one of the inventive embodiments of the invention, after having been deformed; [0031] FIG. 8 is a perspective view of the rivet assembly shown in FIG. 1, after having been deformed, according to the present disclosure; [0032] FIG. 9 is a side elevational view of the rivet assembly shown in FIG. 8; [0033] FIG. 10 is a perspective view of the rivet assembly shown in FIG. 1, after having been deformed, with the proximal end of the mandrel removed; [0034] FIG. 11 is a side elevational view of the rivet assembly shown in FIG. 10; [0035] FIG. 1 lA is a sectional view of the rivet assembly configured with an alternative embodiment; [0036] FIG. 11B is a perspective view of still another embodiment of the inventive rivet assembly; (0037] FIG. 12 is a perspective view of a rivet crimper configured in accordance with the invention; [0038] FIG. 13 is a side elevational view of the rivet crimper shown in FIG. 12; [0039] FIG. 14 is a cross-sectional view of the rivet crimper shown in FIG. 13; [0040] FIG. 15 is an enlarged view of the nose portion of the rivet crimper shown in FIG. 14 with the rivet assembly inserted within the nose and the handles of the rivet crimper in the open position; [0041] FIG. 16 is an enlarged view of the nose portion of the rivet crimper shown in FIG. 14 with the handles of the rivet crimper squeezed together; [0042] FIG. 17 is an enlarged view of the nose portion of the rivet crimper shown in FIG. 14 after the handles of the rivet crimper have returned to the open position, and the rivet body and distal portion of the shaft of the mandrel have separated from the proximal portion of the shaft of the mandrel; [0043] FIG. 18 is an enlarged view of the nose portion of the rivet crimper shown in FIG. 14 after the nose of the rivet crimper has been twisted inwardly thereby pushing the jaws inwardly in order to release the proximal end of the shaft of the mandrel; [0044] FIG. 19 is an enlarged view of the nose portion of the rivet crimper shown in FIG. 14 with the proximal end of the shaft removed therefrom; DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS [0045] A rivet assembly 100, as shown in FIGS. 1-11, is used in a variety of spinal implantation methods and is configured as a stabilization device primarily directed to connect inferior and superior articular processes of superior and inferior adjacent vertebrae, respectively. The rivet assembly 100 can be used as supplemental posterior stabilization in a circumferential or 360 degree fusion or as a stand-alone device for cases with slight posterior instability. Advantageously, the rivet assembly is shaped and dimensioned for use with a transfacet method of implantation where the distal end 120 of the assembly remains buried inside cancellous bone. In contrast to various types of pedicle screws, the inventive rivet assembly 100 is dimensioned to allow a minimal invasion into the pedicle. Furthermore, because the rivet assembly 100 is less rigid than a pedicle screw system, the distribution of axial forces between an implanted intervertebral body and rivet assembly better approximates the natural distribution of these forces between intervertebral discs and supporting structures. The rivet assembly 100 can also be inserted successfully using other methods. One such method is a transfacet method, where the distal end can penetrate outside the cortical bone. Still another method is a translaminar method, where the distal end 120 of the rivet assembly enters the base of the spinous process, continues through the lamina on the contralateral side, on into the base of the transverse process. Finally, a percutaneous approach can be combined with the aforementioned methods and performed in association with the inventive rivet assembly 100.

[0046] Referring initially to FIGS. 1 and 2, a rivet assembly according to the present disclosure is generally depicted as 100. The rivet assembly 100 includes a cylindrical rivet body 102 and an elongate mandrel 104 slidably disposed within and extending through rivet body 102.

[0047] As seen in FIGS. 1-5, rivet body 102 includes a shank 106 having a head 108 formed at a proximal end thereof, a deformable tip 110 formed at a distal end thereof and a through bore 112 extending the entire length thereof. Head 108 includes a body portion 114 having a larger diameter than shank 106 and a tapered forward portion 116 configured to create a smooth interface between head 108 and shank 106. As seen in further detail in FIG. 5, deformable tip 110 includes a plurality of radially spaced and longitudinally extending throughslits 118 thereby defining a plurality of deformable semi-circular webs or leaf portions 120, wherein each leaf portion 120 includes a rounded frontal lip 122. Slits 118 may or may not be evenly spaced from one another. The leafs or webs 120 are configured to engage the bone, preferably the cancellous bone, at the base of the superior articular process of the inferior vertebra, as will be explained herein below.

[0048] Alternatively, as illustrate in FIG. 3A, the shank 106 may have a textured 119 outer surface to better engage the bone. As shown in FIG. 3A, the proximal end of each slit 118 may also have additional relief slits 121 of varying shape and sizes.

[0049] In accordance with yet another configuration, as illustrated in FIG. 3B, the shank 106 may have a weakened portion spaced at a distance from both distal and proximal ends of the rivet body. The portion is provided with a plurality of radially spaced slits 121 defining therebetween a plurality of webs 123. Similarly to the leafs 120, the webs 123 are configured to expand radially outwards to engage the bone, as will be better discussed in reference to FIG. 11A.

[0050] As seen in FIGS. 6 and 7, mandrel 104 includes an elongate shaft 124 having an enlarged head 126 formed at a distal end thereof. The diameter of shaft head 126 approximately corresponds to an outer diameter of shank 106 of rivet body 102 and is provided with an annular rounded proximal surface 128 for providing a smooth transition between the enlarged head 126 and the shaft 124. Elongate shaft 124 of mandrel 104 is further provided with an annular break-off groove 130 formed therearound. Annular break-off groove 130 defines a zone of weakening whereby when shaft 124 of mandrel 104 is pulled through rivet body 102, a proximal end of shaft 124 will separate from a distal end of shaft 124 at the location of break-off groove 130. Between enlarged head 126 and groove 130, shaft 124 is provided with a roughened surface 132 (e. g. , knurling,<BR> longitudinal grooves, annular rings, helical ridges etc. ) completely encircling shaft 124.

Roughened surface 132 functions to provide a frictional fit with the interior surface of shank 106 of rivet body 102 along through bore 112 and act as a vibration-resistant mechanism to insure that the distal end of mandrel 104 does not come out of or become disengaged from rivet body 102 once rivet assembly 100 has been secured into place.

[0051] Alternatively, as shown in FIG. 7A, the shaft 124 of mandrel 104 could have an additional step 119 located on the distal end of the mandrel 104 and cooperating with a shoulder 117 formed on the inner surface of the rivet body 102. The shoulder 117 provides a physical stop for the step 119 of the mandrel 104 limiting the extent of its travel.

[0052] As shown in FIGS. 1,2, 4, and 6, shaft 124 of mandrel 104 is positioned within through bore 112 of rivet body 102 such that the enlarged head 126 of mandrel 104 is adjacent to the deformable tip 110 of rivet body 102. Turning now to FIGS. 4-6 and 8-9, in operation, on pulling mandrel 104 in direction"A", through bore 112 of rivet body 102, rounded surface 128 of shaft 124 interacts with rounded lip 122 of deformable tip 110 such that leafs 120 spread outwardly away from mandrel 104 along radial slits 118 and cause leafs 120 to curl back towards rivet body 102. Finally, as seen in FIGS. 4,6, 10 and 11, once a pulling force exceeding the tensile strength of the mandrel has been reached, the proximal end of shaft 124 will separate or break-off along groove 130 and distal end of shaft 124 will remain frictionally engaged within shank 106 of rivet body 102 due to the frictional coupling of the roughened surface 132 of mandrel 104 with the inner surface of rivet body 102. The distal end of the rivet body 102 can have the shoulder 117 configured to abut the step 119 (FIG. 4) of the mandrel to prevent its displacement through the rivet body.

(0053] FIG. 11A illustrates the rivet assembly having the rivet body 102 configured in accordance with the alternative embodiment shown in FIG. 3B. Multiple webs 123 constitute the weakened region of the rivet body 102. In addition, the distal end 125 of the rivet body 102 is threaded to threadingly engage a distal threaded end of the mandrel 100. As the mandrel 100 advances through the proximal end of the rivet body 102, the webs 123, defined between slits 121, deform to engage the bone, as shown in phantom lines in FIG. 1 lA. While the principle of the engagement is similar to the previously disclosed embodiment having the deformable distal end, instead of a tensile force, a sufficient external torque should be applied to the mandrel 100, which is configured similar to the above disclosed structure, to couple the components of the rivet assembly.

[0054] While the rivet assembly, as discussed above, has substantially the straight rivet body and mandrel, the components of the assembly may have a curved shape, as shown in FIG I I B.

[00551 Referring now to FIGS. 12 to 19, a rivet crimper according to the present disclosure is generally depicted as 200. Rivet crimper 200 includes a handle assembly 202 operatively coupled to a rivet crimping assembly 204. Handle assembly 202 includes a first handle 206 integrally formed with crimping assembly 204, a second handle 208 pivotally coupled to crimping assembly 204 and biasing means 210 disposed between the first and second handles 206 and 208 for maintaining handles 206 and 208 spaced from one another.

[0056] Crimping assembly 204 includes a nose 212 threaded on to the forward end of the crimping assembly 204 via threading means 214. Nose 212 includes a hollow rearward portion 216 and a mandrel shaft-receiving portion 218 which is co-axial with hollow rearward portion 216. Mandrel shaft receiving portion 218 has a diameter which is smaller than the diameter of the hollow rearward portion 216 thereby defining a shoulder 220.

[0057] Crimping assembly 204 further includes a cylinder body 222 slidably disposed within the hollow rearward portion 216, which cylinder body 222 includes frusto- conically shaped forward portion 224 having a smaller diameter opening proximate the shoulder 220 of the hollow rearward portion 216 and a larger diameter opening spaced a distance rearward therefrom. The frusto-conical forward portion 224 defines a first camming surface 226 against which the outer surfaces of jaws 228 contact and slide. The pair of jaws 228 include a pair of substantially parallel row of teeth 230, a forward portion 232 projecting from the forward portion 224 of cylinder body 222 and a chamfered rearward portion 234 defining a second camming surface 236.

[0058] Crimping assembly 204 further includes a plunger 238 having a forward portion 240 configured and adapted to be threaded into or connected to a rearward portion of the cylinder body 222, a central body portion 242 and a rearward portion 244 pivotally connected to linkage 246 pivotally connected to the second handle 208.

[0059] The crimping assembly 204 also includes a piston 248 slidably disposed within the cylinder body 222 and biased via biasing means 250 toward the forward portion 224 of cylinder body 222. Piston 248 includes an angled forward surface 252 configured and adapted to engage the chamfered surface 236 of the pair of jaws 228. In this way, the angled forward surface 252 of the biased piston 248 presses against the camming surface 236 of the pair of jaws 228 to first keep the pair of jaws 228 aligned with each other and to second keep the outer surface of the first pair of jaws 228 pressed against the frusto-conical camming surface 226 of forward portion 224 of cylinder body 222 thereby squeezing the pair of jaws 228 together.

[0060] Use of rivet crimper 200 is as follows. Prior to loading rivet crimper 200 with a rivet assembly 100, handle assembly 202 is maintained in a spaced apart open position whereby the cylinder body 222 is maintained in a forward portion via plunger 238 and linkage 246 and by second keeping the nose 212 in a fully forward disposed position.

Shoulder 220 of nose 212 keeps the pair of jaws 228 partially open (despite the biasing force of 250) to facilitate insertion of the rivet assembly.

[0061] Next, the proximal end of a mandrel shaft 124 of rivet assembly 100 is inserted into the mandrel shaft receiving portion 218 of nose 212. Rivet assembly 100 is inserted into the nose 212 until head 108 of rivet body 102 abuts against the tip of nose 212. To prevent any possibility of uncontrollable displacement of the tip of the mandrel shaft 124 towards the rear end of the rivet crimper 200 which would necessitate disassembly of the nose 212 after the rivet assembly has been placed in the facets, piston 248 is provided with a stop 215. Once shaft 124 is inserted past the mandrel shaft receiving portion 218, shaft 124 engages the pair of jaws 228. Shaft 124 is then inserted into the forward portion 232 of the pair of jaws 228 with a force sufficient to overcome the biasing force of biasing means 250. In this manner, the pair of jaws 228 slide rearwardly against angled forward surface 252 thereby causing the pair of jaws 228 to become further spaced apart in order to accommodate shaft 124 therebetween. Once the insertion force for rivet assembly 100 is removed, the force created by the biasing means 250 pressing the piston 248 into the pair of jaws 228 forces the pair of jaws 228 forward along the first camming surface 226, pressing the rows of the teeth 230 into shaft 124 thereby gripping shaft 124 and preventing the removal of rivet assembly 100 from nose 212 of rivet crimper 200.

[0062] In order to deform rivet assembly 100, handle assembly 202 of rivet crimper 200 is squeezed together thereby drawing linkage 246 and plunger 238 rearwardly. As plunger 238 draws cylinder body 222 rearwardly through hollow rearward portion 216, the pair of jaws 228 gripping shaft 124 draw shaft 124 rearwardly through shank 106 of rivet body 102. As shaft 124 of mandrel 104 is drawn through shank 106 of rivet body 102, the rounded surface 128 of shaft 124 presses into the rounded lip 122 of deformable tip 110 such that leafs 120 spread outwardly away from mandrel 104 along radial slits 118 causing leafs 120 to curl back towards rivet body 102. Once the pulling force reaches a sufficient degree, the proximal end of shaft 124 of mandrel 104 will separate from the remainder of rivet assembly 100 and break-off along groove 130. The break-off groove 130 is positioned such that the distal portion of shaft 124 of mandrel 104 does not protrude out of head 108 of rivet body 102.

[0063] In order to remove the proximal portion that has broken off of shaft 124 from the pair of jaws 228, handle assembly 202 is first returned to the un-squeezed and open position. Nose 212 is then twisted inwardly about threading means 214 such that the overall length of rivet crimper 200 is shorter. Nose 212 is twisted until shoulder 220 in nose 212 contacts and presses against forward portion 232 of the pair of jaws 228 and then twisted further so as to force the pair of jaws 228 rearwardly against the biasing force created by the biasing means 250 and radially outward as a result of the interaction of the rearward chamfered surface 236 and the angled forward surface 252 of piston 248.

By the pair of jaws 228 moving radially outward, the rows of teeth 230 release their grip from around the shaft 124 and the shaft 124 is able to be removed easily from the mandrel shaft receiving portion 218 of nose 212.

[0064] Referring to FIGS. 1 to 19, the method of the present invention will now be described. In general, the method involves the insertion of the rivet assembly 100 starting from the posterior surface of the inferior articular process of the superior vertebra, crossing the facet joint, and on into the superior articular process of the inferior vertebra.

[0065] To secure the facets of the adjacent vertebrae to one another with rivet assembly 100 using rivet crimper 200 disclosed herein, the intended area of operation must first be exposed by entering a patient in accordance with standard surgical procedures. This typically involves a small midline (along the spine column) incision exposing the facets. After the facets of the vertebrae are exposed, the surgeon places a K- wire in the intended location and uses a cannulated drill to create a blind hole across the facet joint to the desired depth. In a preferred method, the drill goes through the inferior articular process of the superior vertebrae, across the facet joint, into the superior articular process of the inferior vertebrae ending at the base of the superior articular process such that the hole formed in the inferior vertebrae solely penetrates the upper cortical surface of the superior articular process and does not completely pass through the inferior vertebrae.

100661 After removing the K-wire and the drill, the surgeon uses a depth gage to measure the depth of the hole and selects rivet assemblies 100 to be used based on their rivet body lengths, body diameters, head diameters, etc. Multiple diameter and length rivet assemblies are envisioned. It is evident that the diameter of each hole drilled is slightly larger than the diameter of each shank 106 so that the rivet body 102 is easily insertable within the hole. Next, the surgeon inserts the proximal end of shaft 124 of rivet assembly 100 into the mandrel shaft receiving portion 218 of rivet crimper 200 until head 108 of rivet body 102 abuts against the tip of nose 212.

[0067] The surgeon then inserts deformable tip end 110 of rivet body 102 through the hole formed in the facets until head 108 of rivet body 102 rests against the outside of the inferior facet of the superior vertebrae. The surgeon then actuates rivet crimper 200 in the manner disclosed above. Rivet crimper 200 exerts a force on the shaft 124 of mandrel 104 so as to pull mandrel 104 through rivet body 102 thereby deforming leafs 120 of deformable tip 110 until shaft 124 of mandrel 104 separates along groove 130.

The distal part of shaft 124 of mandrel 104 stays within the deformed rivet body 102.

The proximal part of shaft 124 remains securely held by jaws 228 in nose 212 of rivet crimper 200. The deformation of leafs 120 secures rivet body 102 in place and the surgeon does not have to be concerned with retrieving the broken off shaft portion from the patient's body cavity.

[0068] Securing rivet assembly 100 with rivet crimper 200 requires very little effort on the part of the surgeon. The surgeon merely squeezes handle assembly 202 of rivet crimper 200 to actuate crimping assembly 204. Rivet crimper 200 does all of the work in securing the rivet assembly 100 in place.

[0069] When rivet assembly 100 is secured in place, the facets of adjacent vertebrae are clamped together between the head 108 and the deformed leafs 120 of deformable tip 110 of rivet body 102. The surgeon then adds bone graft to the appropriately decorticated areas to complete the fusion procedure.

[0070] Although the method described above for inserting the rivet assembly 100 is for an open surgical procedure, the insertion method can easily be adapted to a percutaneous approach. The percutaneous approach would begin with a small stab incision, directed generally perpendicular to the longitudinal direction of the spine column, through which a K-wire could be placed. A cannulated drill is then used to drill the appropriate sized hole over the K-wire. The drill can have a depth stop shaped like head 108 of the rivet body 102 such that the drill only creates holes up to a specific depth.

Such depths can be made to specifically match designated lengths of the rivet assembly 100, thus eliminating the need for a depth gage. A sleeve is then placed over the drill.

Spikes or other attachment means at the end of the sleeve ensure its position relative to the bone. The drill and K-wire are removed. While loaded in the crimping assembly 200, the rivet assembly 100 can then be inserted through the sleeve into the hole. The crimping assembly 200 is then operated as described above, implanting the rivet assembly 100. The crimping assembly 200 is then withdrawn from the sleeve, and the sleeve is removed. The proximal part of shaft 124 can then be safely removed from jaws 228 in nose 212 of rivet crimper 200.

[0071] It is preferred to drill a blind hole toward the pedicle to keep the deformed webs 120 of rivet assembly 100 within the cancellous bone and keep the exposed rivet profile to a minimum. As mentioned above, however, other methods (transfacet, translaminar, etc. ) where webs 120 deform inside or outside the bone (facet) are also envisioned.

[0072] Although the current technique describes using the rivet alone to stabilize the facets, it is envisioned that the rivet assembly 100 could be used with other components (i. e. , plates, etc. ), in other locations, and applications (i. e. , trauma, etc.).

[0073] Additionally, arcuate rivet assemblies are also envisioned, which may allow the surgeon to more easily insert the rivets through the facets. With an arcuate rivet assembly, a flexible drill would be necessary to drill over a similarly curved K-wire.

[0074] It will be understood that various modifications may be made to the embodiments disclosed herein. It is envisioned to make the inventive rivet assembly from a variety of materials including, but not limited to, metals, such titanium, stainless steel, biodegradable, plastic or any material transparent when used in association with modern diagnostic procedures. The number and geometry of the slits in the rivet body can vary depending on the material properties of the rivet body and the manner of deformation desired. The size and the shape of the mandrel groove can also vary depending on the mandrel's material properties and the amount of deformation desired in the rivet body. In addition, the present disclosure relates to a peel type rivet, however, it is envisioned that a rivet undergoing an annular-ring-type deformation is also possible.

Moreover, it is envisioned that the outer surface of the rivet body can be roughened (e. g., knurled, grooved, spiked, etc. ) in order to provide the rivet body with better holding power. Therefore, the above description should not be construed as limiting, but merely as exemplifications of preferred embodiments. The kit also includes an instrumentation/implant case specifically configured to contain variously shaped and dimensioned implants and rivets, as well as the inventive crimper assembly. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.