Polyaxial screw

A polyaxial screw is used for connecting vertebrae to rods in spinal surgery. It is essentially a screw whose spherical head is enclosed on a housing, which allows the screw a range of motion along several different axes relative to the housing. The ball joint allows the surgeon some flexibility in placing the screws.

It has also been hypothesized that polyaxial screws add a safety benefit by failing in the housing/screw interface before breaking in the shaft of the bone screw or in the orthopaedic rod.