Joint fusion implant and methods
An implant for fusing a joint between first and second bone portions. The implant includes a screw member, and a washer polyaxially rotatable relative to the screw member. The screw member includes a head, a lag zone, and a threaded engagement zone. The implant includes a fusion zone for joint compression, extending from the washer to the proximal end of the engagement zone. Fenestrations may be present in the fusion zone. The length of the fusion zone ranges from about 10 mm to about 37 mm. Different surface finishes including roughened and non-roughened may be applied selectively to selected portions of the implant. In an embodiment, the joint is a sacro-iliac joint, and upon implantation the implant extends from the exterior of the ilium, across the joint and into the sacral vertebral body. Instrumentation and methods for preparing the joint and implanting the implant are disclosed.
1. A system for compressing a joint between a first bone portion and a second bone portion, the system comprising:
an instrument for excising a cavity between the first bone portion and the second bone portion, the instrument having a handle and a blade assembly, wherein the blade assembly is movable between a retracted configuration and an extended configuration relative to an instrument longitudinal axis to define a cutting radius; and
an implant for providing compression across the first bone portion, the cavity, and the second bone portion to fuse the joint, wherein the implant comprises:
a screw member having a screw head, and a screw body projecting distally from the screw head along a longitudinal axis to a screw distal end, the screw body comprising a lag zone and a threaded engagement zone;
a washer member having a proximal side and a distal side, wherein the screw head is received in the washer member, and the screw body projects distally from the washer member; and
an implant fusion zone is defined to extend from the distal side of the washer member to a proximal end of the screw threaded engagement zone.
2. The system of claim 1 , wherein the lag zone is non-threaded and extends from the screw head distally to the threaded engagement zone, and the threaded engagement zone extends distally from the lag zone to the screw distal end.
3. The system of claim 2 , wherein the screw body further comprises a central longitudinal bore extending from the screw head to the screw distal end, and the lag zone comprises a fenestration opening into the central longitudinal bore.
4. The system of claim 1 , wherein the washer member further comprises a semispherical capsule between the proximal side and the distal side, and the screw head is received in the semispherical capsule to permit polyaxial angulation of the washer member with respect to the screw member.
5. The system of claim 4 , wherein the washer comprises a bore having a central bore axis, wherein the permitted polyaxial rotation angulation of the washer member central bore axis with respect to the screw member longitudinal axis ranges from at least −8 degrees to at least +8 degrees.
6. The system of claim 5 , wherein an overall length of the implant, measured from the distal side of the washer to the screw distal end when the washer central bore axis is coaxial with the screw member longitudinal axis, ranges from about 40 mm to about 110 mm.
7. The system of claim 1 , wherein the length of the implant fusion zone ranges from about 10 mm to about 37 mm.
8. The system of claim 1 , wherein the implant is a sacro-ilial fusion implant, wherein the joint is a sacroiliac joint, the first bone portion is an ilium, the second bone portion is a sacrum, and the cavity is excised between the ilium and the sacrum; wherein, when the implant is installed across the sacroiliac joint, the distal side of the washer member is in contact with an exterior surface of the ilium, the implant fusion zone extends at least partially across the sacroiliac joint and the cavity, and the threaded engagement zone is embedded in the sacrum.
9. The system of claim 1 , wherein an outer diameter of the cavity is determined by the instrument cutting radius, and wherein the maximum outer diameter of the implant is less than the cavity outer diameter.