Spinal facet compression screw with variable pitch thread zones and buttress head

Abstract

A surgical implant comprising a screw element having a screw head, a first thread having a first thread pitch, a second thread having a second thread pitch and an intermediate portion coupling the first and second thread pitches with the first and second thread pitches being different. The implant has a buttressing head associated with the first thread, and it is dimensioned to be larger than a diameter of the first threads to provide external buttressing as the first and second threads compress a first bone and a second bone together.

What is claimed is: 
     
         1 . A surgical implant comprising:
 a screw element having a screw head, a first thread having a first thread pitch and a second thread having a second thread pitch; and   said screw head defining a tool attachment zone;   a buttressing head associated with said first thread and being dimensioned to be larger than a diameter of said first thread to provide external buttressing as said first thread and said second thread compress a first bone and a second bone together.   
     
     
         2 . The surgical implant as recited in  claim 1  wherein said first thread pitch is smaller than said second thread pitch. 
     
     
         3 . The surgical implant as recited in  claim 1  wherein said screw element comprises at least one locking slot to facilitate allowing for bone growth over said screw element and helping to prevent said screw element from loosening. 
     
     
         4 . The surgical implant as recited in  claim 3  wherein said at least one locking slot is linear. 
     
     
         5 . The surgical implant as recited in  claim 3  wherein said screw element comprises a plurality of locking slots. 
     
     
         6 . The surgical implant as recited in  claim 5  wherein said plurality of locking slots are located in at least one or both of said first thread and said second thread. 
     
     
         7 . The surgical implant as recited in  claim 6  wherein said plurality of locking slots are located in said first thread. 
     
     
         8 . The surgical implant as recited in  claim 1  wherein said screw head comprises third threads at said tool attachment zone to allow for engagement of a tool locking sleeve. 
     
     
         9 . The surgical implant as recited in  claim 8  wherein said third threads have a handedness that is opposite the handedness of each of said first thread and said second threads. 
     
     
         10 . The surgical implant as recited in  claim 1  wherein said first thread pitch and said second thread pitch are different so that when said first thread threadably engages and drives said first bone to be fused at a first rate and said second thread threadably engages and drives said second bone to be fused toward said first bone at a second rate, wherein said second rate is greater than said first rate. 
     
     
         11 . The surgical implant as recited in  claim 1  wherein said buttressing head has a generally planar bone-engaging surface at an end of said first threads. 
     
     
         12 . The surgical implant as recited in  claim 1  wherein said first thread is a proximal thread and said second thread is a distal thread, said first thread and said second thread driving said first bone and said second bone, respectively, towards said buttressing head at different rates. 
     
     
         13 . The surgical implant as recited in  claim 1  wherein said buttressing head is located between said tool attachment zone and said first thread. 
     
     
         14 . The surgical implant as recited in  claim 1  wherein said first and said second thread pitches are different. 
     
     
         15 . The surgical implant as recited in  claim 1  wherein said screw element comprises an intermediate portion coupling said first thread pitch and said second thread pitch; 
     
     
         16 . The surgical implant as recited in  claim 15  wherein said intermediate portion and said buttressing head are not threaded. 
     
     
         17 . The surgical implant as recited in  claim 13  wherein said first and said second thread pitches are different. 
     
     
         18 . The surgical implant as recited in  claim 17  wherein said screw element comprises an intermediate portion coupling said first thread pitch and said second thread pitch; 
     
     
         19 . A surgical implant comprising:
 an elongated body having a first end and a second end;   a screw head associated with said first end;   a first thread having a first thread pitch associated with said first end, a second thread having a second thread pitch and an intermediate portion coupling said first and second thread pitches, said first and second thread pitches being different; and   said screw head defining a tool attachment zone;   a buttressing head situated between said first thread and said screw head;   said buttressing head being dimensioned to be larger than a diameter of said first threads to provide external buttressing to a first bone as said first threads and said second threads compress a second bone against said first bone.