Hemiarthroplasty Head Comprised of an outer cobalt chrome shell, the pre-assembled Bipolar head contains a polyethylene liner. This in turn consists of a captive cobalt chrome femoral head which locates onto the taper (available in 12/14) of a femoral stem. Bipolar femoral heads are used in hemiarthroplasty procedures where the femoral head requires replacement but the acetabulum does not. In such cases the amount of wear against the natural acetabulum is minimised by using a bipolar head, where the majority of movement occurs at the inner metal-on-polyethylene bearing and at the extremes of range of motion, and the large diameter head articulates directly against the natural acetabulum. The instrumentation used for implantation of the Bipolar head is simple and easy to use due to the pre-assembled nature of the implant.