A bone screw mating seat that grips the head of the bone screw allowing a rod to be secured to it

摘要

A polyaxial bone securing system (10) is disclosed. A bone securing member (12) including a threaded shaft portion (14) and a head portion (16) is inserted into a bore through a coupling element (22). The coupling element also includes a rod receiving channel (26) perpendicular to the bore. A seat adjacent a lower opening (24) in the bore includes a discrete number of non-contiguous radially expandable contact elements. A saddle member (29) is disposed within the bore of the coupling element (22), the saddle member (29) being located between a longitudinal spinal rod when inserted in the rod receiving channel (26) and the head portion (16) of the bone securing member (12). A mating cap (28) secures the longitudinal spinal rod and the bone securing member (12) with respect to the coupling element (22) by engaging with the coupling element (22). The head portion (16) is pressed into the contact elements by the compression of the spinal rod by the mating cap (28) causing the coupling element (22) to be locked into its current orientation.