A comparitive study of a mobile bearing hip system with unipolar hip replacement in patients requiring a unipolar hip replacement for metastatic bone disease.

This study aims to assess whether a mobile bearing hip replacement will reduce the incidence of groin pain compared to that experienced with a unipolar hip replacement without an increased risk of dislocation. Who is it for? You may be eligible for this study if you have been diagnosed with metastatic disease that has spread to the proximal femur – thigh bone – which requires surgical replacement of the femoral head. Trial Details In this study, you will receive either a Unipolar hip replacement which is a hip replacement that replaces only the femoral side, or a Mobile bearing hip replacement which is a hip replacement that replaces the femoral side and lines the acetabulum, the socket of the pelvis. Following either of these interventions, you will then be assessed through the use of questionnaires and x-rays. Metastatic bone disease may affect only the proximal femoral side of the hip joint. Conventional surgical treatment consists of a unipolar hip replacement because the acetabulum is not affected and total hip replacement in this situation has been associated with an increased risk of hip dislocation. Unipolar hip replacements have a much lower risk of dislocation but the articulating surface consists of a metallic head against articular cartilage of the acetabulum. This always results in degradation of the articular surface of the acetabulum and pain. A new device, the ADMX3 mobile bearing hip system (Stryker, NJ, USA) is derived from a dual mobility cup concept which has a proven track record of decreased dislocation and increased implant stability. Instead of the metallic head grinding into the acetabular cartilage, this system is a two-piece component with an acetabular cup that replaces the articular surface into which a polyethylene insert is added into which the metallic head of the proximal femur is inserted. This results in articulation both between the head and insert and the insert and the acetabular cup, not against articular cartilage. This system also has a notch in the anterior portion of the cup which reduces the risk of cup and iliopsoas tendon impingement which is also a source of groin pain post hip replacement. Theoretically it should therefore reduce pain and not increase the risk of dislocation but it is not known if it will improve the incidence or severity of post-operative groin pain that is associated with a unipolar or bipolar hip replacement.