Bone fixation assembly and method of securement

Abstract

A bone plate is provided for fixation of spaced vertebra. The bone plate has at least one through passage for securing the plate to bone with a bone fixation screw. The threaded shaft of a bone fixation screw is inserted through a bushing located in the through passage of the bone plate and the screw is thereby threadably secured to the underlying bone and the bushing is then compressed inward against the head of the screw with cams that are actuated by rotating the bushing in the through passage whereby the screw is locked relative to the bone plate. The bushing is not only compressed inwardly against the head of the screw but is also compressed downwardly by the cams into a seat to clamp separate elements of the bone plate together.

1 . A method for securing a bone plate having a through passage to bone, the method comprising the steps of: 
 inserting a bushing into the through passage;    inserting the shaft of a fastening screw having a head and a threaded shaft through the bushing located in the through passage of the bone plate;    threading the fastening screw into a bone until the screw head is drawn into an interior socket bore in the bushing; and    compressing the bushing inward against the head of the screw with cam means actuated by rotating the bushing in the through passage whereby the screw is locked relative to the bone plate.    
   
   
       2 . The method of  claim 1  wherein the step of compressing also includes compressing the bushing downwardly into a seat to clamp separate elements of said bone plate together.  
   
   
       3 . The method of  claim 1  wherein threading of the screw includes rotating the screw clockwise and rotating the bushing includes rotating the bushing counterclockwise.