US Patent 6843791 Locking cap assembly for spinal fixation instrumentation

A locking cap assembly for locking a spinal fixation element to a spinal fixation element receiving body includes an outer and inner locking element. The outer locking element has a proximal mating element, and a engagement element formed on the inner surface adjacent the distal end for engaging a spinal fixation element receiving body so as to close the spinal fixation element to the spinal fixation element receiving body upon tightening. The inner locking element has a deformable spinal fixation element contacting ring disposed on its distal end and a proximal mating element on its proximal end rotatably mated to the outer locking element proximal mating element so that the inner locking element is rotatably mounted within the outer locking element. Tightening the spinal fixation locking cap assembly to the spinal fixation element receiving body causes the deformable spinal fixation element contacting ring to contact the spinal fixation element and to deform the deformable spinal fixation element contacting ring to provide secure four point locking of the spinal fixation element within the spinal fixation element receiving body.