Facet fixation prosthesis

Abstract

A facet screw system for surgical implantation into bone tissue having a shaft, a compression member and a washer. The shaft includes a shaft having a bone engaging portion and a compression member engaging portion. The compression member includes a spherical head portion having a recess for engaging with a driving instrument, and an elongated coupling portion having internal threads for coupling with the compression member engaging portion of the shaft and a washer coupled to the spherical head portion of the compression member and having a plurality of bone engaging protrusions. The washer is adapted to be polyaxially rotatable with respect to the compression member.

What is claimed is: 
     
         1 . A facet screw system for surgical implantation into bone tissue, comprising:
 a shaft, the shaft having a bone engaging portion, a graft window, and a compression member engaging portion;   a compression member, the compression member comprising:
 a spherical head portion having a recess for engaging with a driving instrument, and 
 a coupling portion for coupling with the compression member engaging portion of the shaft; and 
   a washer coupled to the spherical head portion of the compression member,   wherein a diameter of the spherical head portion of the compression member is greater than a diameter of a bottom portion of the washer.   
     
     
         2 . The facet screw system of  claim 1 , wherein the facet screw system is cannulated for receiving a guide wire. 
     
     
         3 . The facet screw system of  claim 1 , wherein a flute is provided at a distal end of the shaft. 
     
     
         4 . The facet screw system of  claim 1 , wherein the washer comprises a plurality of slits extending from a bottom portion of the washer through the top portion of the washer. 
     
     
         5 . The facet screw system of  claim 1 , wherein the spherical head of the compression member is configured to receive the driving instrument. 
     
     
         6 . The facet screw system of  claim 1 , wherein the shaft portion comprises a recess for receiving the driving instrument. 
     
     
         7 . The bone screw of  claim 1 , wherein the shaft portion is configured with one type of thread and the compression member engaging portion is configured with another type of thread. 
     
     
         8 . The bone screw of  claim 1 , wherein the screw is made from stainless steel alloys, titanium, titanium based alloys, or polymeric materials. 
     
     
         9 . A facet screw system for surgical implantation into bone tissue, comprising:
 a shaft, the shaft having a bone engaging portion, a graft window, and a compression member engaging portion;   a compression member having a proximal end and a distal end, the compression member comprising:
 a spherical head portion located at the proximal end and having a recess for engaging with a driving instrument; and 
 an elongated coupling portion having internal threads for coupling with the compression member engaging portion of the shaft; and 
   a washer having a ridge positioned on a top portion of the washer and plurality of bone engaging protrusions on a bottom portion, wherein the washer is polyaxially rotatable with respect to the compression member.   
     
     
         10 . The facet screw system of  claim 9 , wherein the facet screw system is cannulated for receiving a guide wire. 
     
     
         11 . The facet screw system of  claim 9 , wherein a flute is provided at a distal end of the shaft. 
     
     
         12 . The facet screw system of  claim 9 , wherein the spherical head of the compression member is configured to receive the driving instrument. 
     
     
         13 . The facet screw system of  claim 9 , wherein the shaft portion comprises a recess for receiving the driving instrument. 
     
     
         14 . The bone screw of  claim 9 , wherein the shaft portion is configured with one type of thread and the compression member engaging portion is configured with another type of thread. 
     
     
         15 . The bone screw of  claim 9 , wherein the screw is made from stainless steel alloys, titanium, titanium based alloys, or polymeric materials. 
     
     
         16 . A facet screw system for surgical implantation into bone tissue, comprising:
 a shaft, the shaft having a bone engaging portion, a graft window, and a compression member engaging portion;   a compression member having a proximal end and a distal end, the compression member comprising:
 a spherical head portion located at the proximal end and having a recess for engaging with a driving instrument; and 
 an elongated coupling portion having internal threads for coupling with the compression member engaging portion of the shaft; and 
   a washer having a plurality of bone engaging protrusions on a bottom portion, the washer being coupled to the spherical head portion of the compression member, wherein the washer comprises a plurality of slits extending along a top portion of the washer, wherein the slits extend to an edge of the top portion of the washer and enable engagement with the compression member.   
     
     
         17 . The bone screw of  claim 16 , wherein the slits do not extend through the bottom portion. 
     
     
         18 . The bone screw of  claim 16 , wherein an outer diameter of the elongated coupling portion of the compression member is substantially the same as an outer diameter of the bone engaging portion of the shaft. 
     
     
         19 . The bone screw of  claim 16 , wherein the washer includes an opening extending through the top portion and the bone engaging portion, and a diameter of the opening being greater in the bone engaging portion relative to the top portion. 
     
     
         20 . The bone screw of  claim 16 , wherein the washer extends around an entire periphery of the compression member.