BONE FIXATION IMPLANT SYSTEM AND METHOD

[0001] This application claims priority from U.S. Provisional Patent Application Ser. No. 60/938,886, filed May 18, 2007; and is a continuation-in-part of U.S. patent application Ser. No. 10/973,524, filed Oct. 26, 2004, which is a continuation-in-part of co-pending U.S. patent application Ser. No. 10/683,076, filed Oct. 10, 2003, which claims priority to U.S. Provisional Patent Application Ser. No. 60/417,543, filed Oct. 10, 2002. The entire content of each application is incorporated herein by reference.

[0002] This invention relates to bone arthrodesis, and more particularly to bone fixation implants and systems and methods for installing such implants.

[0003] Bone arthrodesis or fusion is a process used to assist in the healing or stabilization of impaired bones or joints. In particular, facet arthrodesis is used to fuse the superior and inferior facet in spinal treatment operations, Prior art systems and methods have used bone screws which are screwed through the superior and inferior facets to immobilize the joint so as to permit the adjoined bone sections to fuse together. Wire has also been used to loop around the facets to immobilize the joint. The surgical procedures that must be performed to implant the screws or wires are difficult and time consuming. There is therefore a need for improved bone fixation implants, devices and methods.

[0004] This invention resides in a bone-fastening system. While the described embodiments are oriented toward direct facet fixation, one of skill in the art will appreciate that system and method may be modified for other applications, including translaminar facet fixation and the setting of fractures.

[0005] The system includes an implant with a threaded screw, a distal nut with a threaded bore, and a proximal washer which may also be threaded. An instrument for implanting the implant includes a handle and a barrel terminating in a holder for the washer. A c-shaped bridge assembly has a first end connected to the barrel and a second end including a holder for the nut in axial alignment with the washer. A manually operated control on the instrument, coupled to an elongated element in the barrel, causes the washer to move toward the nut, thereby applying compressive pressure to bone portions to be fastened together. A drive mechanism disposed within the barrel has a distal end with a holder for the screw and a proximal end that is turned by a user, thereby advancing the screw through the washer to the nut to fasten the bone portions under compression. A separate control is used to release pressure on the elongated element in the barrel, enabling the implant to be easily removed from the implant once in position.

[0006] In the preferred embodiment, the controls are triggers that are squeezed toward the handle by a user. The nut may include opposing side cut-outs that extend into the threaded bore, and the holder for the nut may include a pair of opposing side tabs that engage with the cut-outs during placement of the nut. The opposing side tabs are deformed outwardly when the screw is advanced through the nut, thereby enabling the bridge assembly to be remove from the implant. The nut may further include opposing side cut-outs that do not extend into the threaded bore, with the holder for the nut include a pair of opposing outriggers that engage with the cut-outs to enhance stability placement and fastening of the nut.

[0007] The holder for the washer may be coupled to a manually operated control enabling a user to orient the washer for improved conformity with a bony surface. In the preferred embodiment, the screw includes a pointed tip that self-taps through bone, and the nut and washer nut and washer have differently angled bone-contacting surfaces with bone-penetrating spikes, neither of the surfaces being perpendicular to the alignment axis.

[0048] Co-pending U.S. patent application Ser. No. 10/973,524, the entire content of which is incorporated herein by reference, describes a bone fixation implant system and method particularly useful for percutaneous facet fixation during minimally invasive surgical procedures. The system includes an implant for bone arthrodesis and a bone fastening device. The implant includes a fastener with an elongated shaft having a head at one end and a bone-piercing point at the opposite end. A first washer has structure for engaging the head of the shaft so as to be polyaxially pivotable with respect to the head. A locking member has structure for engaging the shaft. The locking member can have a second washer pivotally engaged thereto. The bone fastening device can include an elongated cannula with a collet for detachably engaging the first washer and for advancing the first washer. Structure is provided for engaging the fastener and for advancing and rotating the fastener through the collet and through the first washer. The bone arthrodesis device further includes a lower end portion extending from the cannula. The lower end portion has structure for detachably engaging the locking member. The fastener, first washer, and locking member are aligned such that the advancing fastener will advance through the first washer, drill through the bone, and move into the locking member. A method for performing bone arthrodesis is also disclosed.

[0049] The following description details improvements to facet fixation apparatus and methods, including the system and methods set forth in application Ser. No. 10/973,524 referenced above. FIG. 1A is a side view of an improved facet gun described in U.S. Provisional Application Ser. No. 60/938,886, the entire content of which is also incorporated herein by reference. FIG. 1B is a front view. FIG. 1C is a side view with a cover removed showing internal mechanisms. FIG. 1D is a back view, FIG. 1E is a top view, and FIG. 1F is a cross-section. As with the gun described in the '524 application, the fastener is driven with handle 102 which makes a ratcheting connection through the mechanism depicted in the cross-section of FIG. 1F. An improvement is tab 100 which is coupled to the washer described in further detail below. Right-left movement of the tab 100 also moves the washer slightly clockwise and counter-clockwise, thereby providing improved orientation of the washer relative to recipient bone-engagement surfaces.

[0050] FIG. 2A is a side view drawing of a disposable barrel assembly 200 that mounts to the gun body of FIG. 1 by way of threaded coupler 202. FIG. 2B is a bottom view, FIG. 2C is a top view, FIG. 2D is an oblique view, FIG. 2E is a front view, and FIG. 2F is a back view. These figures show the barrel assembly without the screw, nut or washers in position. One improvement over previous designs is the provision of distal prongs 210, 212, which fit into slots in the nut described below. These prongs, which are separated by the advancing fastener, hold the distal implant components in position until the fastener is advanced.

[0051] FIG. 3A is an oblique drawing of the transfacet barrel assembly with a temporary retainer 300 in place. FIG. 3B is an oblique drawing of the distal end of the barrel assembly with the retainer removed showing the screw 302, washer 304 and nut 306.

[0052] FIG. 4 shows different views of a bridge finger release, better illustrating spreadable prongs 210, 212. FIG. 5 shows different views of a bridge mount, and FIG. 6 shows different views of a flap nut. These drawings better illustrate side slots 602, 604 which receive prongs 210, 212. FIG. 7 shows a blank version of the nut of FIG. 6 and a deformed version wherein slot 702 is spread prior to use. With this design, the advancing screw straightens the deformation back out with a residual interference that locks the two components in position. FIG. 8 shows different views of a PCS nut, and FIG. 9 shows blank and deformed processes. FIG. 10 is an oblique drawing which shows the barrel assembly with nut and washer in position.

[0053] FIG. 11 is an oblique back view of a further improved facet gun apparatus according to the invention. In this case, the barrel assembly 1102 including bridge assembly 1104 is permanently affixed to the body of the gun 1106. This is not necessary to the invention, however, as it is contemplated to have bridge assembly preloaded with fasteners, enabling the bridge assembly and fasteners to become coupled to a barrel assembly and gun which is not disposable. In the case of FIG. 11, however, all components being integrally fabricated results in a disposable item.

[0054] Continuing the reference to FIG. 11, handle 1108 is used to compress the proximal washer against the distal nut, with the advancement of the screw being done manually by coupling a suitable drive instrument to socket 1110. This not only simplifies the overall design, but provides the surgeon with tactile feedback as to the extent of screw advancement, thereby minimizing over-tightening. Further improvements includes the provision of a hard stop 1112 on the proximal drive end, causing advancement to be terminated at a certain extent, thereby further minimizing over-tightening situations.

[0055] Continuing the reference to FIG. 11, the further improvements in the design is the provision of a release lever 1114, which disengages handle 1108, allowing the bridge to be removed from the fastened implant once secured in position. The design continues to incorporate tab 1116, which allows washer 1120 to rock back and forth for better cooperation with patient physiology.

[0056] FIG. 12 is an exploded view of the instrument of FIG. 11, showing how far fewer components are necessary, as compared to previous designs. With the use of a manually-operated mechanism to advance screw 1202, the need for complex ratcheting mechanisms has been eliminated. FIG. 12 also better illustrates cupola tube 1204, which is the element used to apply pressure to washer 1120 against nut 1122. FIG. 13A is a top-down view of the gun depicted in FIGS. 11 and 12. FIG. 13B is a side view; FIG. 13C is a bottom view; FIG. 13D is a back view; and FIG. 13E is a front view. FIG. 14A is an oblique, exploded view of the bridge assembly 1104 from a rearward perspective. FIG. 14B is an oblique representative from a front perspective, and FIG. 14C is a side view. The design continues to incorporate prongs 1402, 1404 which engage with indents in the nut and spread with advancement of the screw. However, an improvement includes outriggers 1406, 1408 which do not expand. This facilitates a straightforward release of the bridge assembly from the nut once in position, while maintaining stability and controlled movement of the gun overall.

[0057] FIG. 15 provides different views of an improved nut according to the invention. Slot 1502 engages with the outriggers just described, whereas intents 1504, 1506 are used to receive the prongs 1402, 1404. Note that the threads are visible through these intends, which is the reason why the prongs are moved apart as the screw is advanced. Further improvement is the use of differently positioned and extended fangs 1510, which facilitate better penetration and fixation. FIG. 16A is a bottom view of the improved bridge assembly; FIG. 16B is a side view; FIG. 16C is a front view; and FIG. 16D is a back view. These views better show outriggers 1406, 1408 and spreadable fingers 1402, 1404. FIG. 17A is one view of an improved driver according to the invention, and FIG. 17B is a different view of that improved driver. In contrast to previous designs, which required a two-part installation process, this improved driver allows for a one-step assembly and use process. The driver simply slides into position, enabling the practitioner to immediately begin the threading operation. FIG. 17C is an exploded isometric drawing of the driver assembly. FIG. 18 shows the bridge assembly from different perspectives, with the distal nut in position.