Polyaxial bone screw

Abstract

A polyaxial bone screw assembly includes a threaded shank body having an upper capture structure, a head, a retaining ring and a nut. The external capture structure surface includes a threaded portion and a smooth portion; the smooth portion for slidably mating with the retaining ring and the threaded portion for rotatable attachment to the nut within a cavity of the head. The nut fixes the retaining ring to the shank and also provides a tool engagement formation for driving the shank body into bone.

What is claimed and desired to be secured by Letters Patent is as follows: 
     
         1 . A polyaxial bone screw assembly comprising:
 (a) a shank having a body adopted for fixation to a bone and an upper capture structure;   (b) a head having a cavity and a lower opening communicating with the cavity; the opening having a diameter sized and shaped to receive the shank upper capture structure into the cavity;   (c) a retainer that is downloaded into the cavity and has a diameter larger than the cavity lower opening; the retainer having a pass through bore sized and shaped to receive the shank capture structure with the shank extending above the retainer; and   (d) a fastener securable to the shank upper capture structure above the retainer so as to lock the shank and retainer together.   
     
     
         2 . The assembly of  claim 1  wherein the head has an upper channel adapted to receive a rod and the shank, when fully assembled with the head, extends into the channel. 
     
     
         3 . The assembly according to  claim 2  including a rod received in the channel and a closure threadably received in the channel to capture the rod in the channel. 
     
     
         4 . The assembly of  claim 1  wherein the fastener is a threaded nut. 
     
     
         5 . A method of use of the assembly according to  claim 1  including the step of assembling the head, the shank, the retainer and the fastener at a factory prior to use of the assembly in a patient. 
     
     
         6 . The method according to  claim 5  including the step of fixedly locking the fastener to the shank to prevent removal of the fastener from the shank after assembly.