Introduction

This procedure involves replacing the surface of the femoral head (top of thigh bone) where the arthritic disease has caused loss of the normal smooth lining of the joint. It also involves the standard removal of arthritic bone from the socket of the hip joint with the introduction of a metal hemispherical component into the pelvis.

The head of the femur is therefore reshaped to accept a metal cap, hence preserving some more head and neck bone than a traditional total hip replacement.

Advantages This procedure is carried out in younger patients with a more active lifestyle. The main advantage to the patient is preservation of bone stock in the femur which means that if revision surgery is necessary in the future, then this can be theoretically easier. It also allows the use of a large metal femoral head which gives a very good range of movement and stability of the hip. This can however be achieved now with more traditional hip replacements as well. Having a metal on metal bearing surface is also associated with a low wear rate.

Disadvantages

The surgery is generally more technically demanding and cannot be done easily through a small incision. There are more muscle releases required in order to reshape the femoral head.

There is also a risk of femoral neck fracture as the neck of the bone is preserved. There can be significant stress on the bone at this level which can lead to fracture. The risk of this is maximal within the first 3 months and is quoted at about 1.5%. This problem is unique to resurfacing as with traditional hip replacements most of the head and neck of the femur is cut off and discarded.

Resurfacing is not generally appropriate for patients with a significant difference in their leg lengths because of arthritis. Other significant biomechanical abnormalities are also difficult to correct with this type of hip replacement.

Avascular necrosis of the femoral head, which has been preserved, can occur and may lead to early failure of the resurfacing. This essentially means that the head does not have a good enough blood supply either before or after the surgery to stay alive. It can therefore collapse leading to problems.

Metal ions are an unknown quantity in hip replacement surgery. This is not unique just to resurfacing but is relevant to all metal on metal hip replacements. When two metal surfaces move together, metal ions are produced. Research has shown that the level of cobalt and chromium in the tissues rise after this type of hip replacement. It is unclear as to whether this is a potential problem, but the majority of hip surgeons concur that in a patient with good health and no kidney problems that there is no current evidence to suggest not using this bearing surface. The benefits of low wear rates, combined with improved biomechanics would seem to outweigh the metal ion issue. This is something that is being monitored closely by the profession. Most surgeons however would not offer metal on metal to patients with known problematic metal allergies or women of child bearing age who plan to have children. The latter is as a result of potential crossing of the metal ions into the womb across the placenta, to the foetus.

Indications

Clearly resurfacing is not appropriate for every patient. In general therefore it is offered only to patients with a high activity level who have minimal loss of bone architecture. In general therefore, this applies to males below the age of 65yrs and females below 55yrs. The difference is due to the higher incidence of osteoporosis in females at a younger age.

Contraindications

Patients with loss of bone architecture and poor bone quality, focal bone defects and abnormal hip anatomy are unsuitable for resurfacing.