Introduction
Resurfacing of the hip is not new, although it is now very widely discussed in hip replacement circles. The principle of resurfacing is to reduce, as much as possible, the amount of bone that is removed from a patient at the time of surgery. It makes sense to remove a small quantity of bone on the first occasion so that there is more available for subsequent operations.
A full resurfacing involves placing a cap over the upper end of the femur (femoral head) and, usually, a metal liner within the hip socket (acetabulum). This gives a low-friction, metal-on-metal articulation with minimal bone removal. The resurfacing components have a wider diameter than hip replacement components, which makes dislocation of a resurfacing a very unlikely complication.
Although the concept of minimal bone removal is attractive, there are several question marks over resurfacing. It is now known that modern designs have a better than 95% chance of lasting 8 years or more. This is a much better result than the earlier designs of hip resurfacing, implanted in the late 1970s and early 1980s, when over 30% would fail within three to four years. However, the long-term outcome for modern resurfacings is still not known but there appears little doubt that current designs are more reliable than their forefathers.
A metal-on-metal articulation, made from cobalt-chrome, can increase the levels of cobalt and chromium in a patient’s blood after hip resurfacing. Sometimes these levels can be more than ten times normal. Is this a problem? It is difficult to say, as it is known that long-term exposure to some metals can be associated with tumour formation. However, current research suggests that this is not a significant risk of modern resurfacings but quantification of this risk is almost impossible.
Hip resurfacing, showing good preservation of the upper thigh bone.
The socket has not been replaced here, though can be so if required.
Fracture of the femoral neck is seen in about 2% of hip resurfacings and normally occurs within three months of the operation. This risk also applied to the earlier designs. Should this happen, then it is most likely the patient would need a further operation, probably to convert their resurfacing to a total hip replacement.
Interestingly, although the aim of a resurfacing is to preserve a patient’s bone, it is not possible to resurface a hip without removing any bone at all. In fact, a resurfacing removes 34% less bone than a total hip replacement. All of this saving is on the femoral side. This is because the acetabular component of a resurfacing tends to be larger than the acetabular component of a hip replacement. Theoretically, this may cause problems when the resurfacing is eventually converted to a total hip replacement, as the surgeon will be faced with a larger-than-normal hole in the patient’s pelvis with which to deal.
The logic of conserving bone can also be applied to a full resurfacing itself. That is, frequently at surgery arthritic changes appear confined to only a small area of the hip joint, often the very top of the femoral head. This is certainly often the situation for a condition known as avascular necrosis (or osteonecrosis). If so, then one might reasonably ask why it is necessary to resurface the whole hip when the pain is arising from such a small area. This is when a partial resurfacing may be indicated. This is a quick procedure, demanding no more than 24 hours in hospital, when a small cobalt-chrome disc is placed over the damaged area. The socket is not touched at all. The disc can be inserted either through a very small incision or even with the assistance of an arthroscope, a keyhole-viewing device.
Partial resurfacing, showing a very limited degree of bone removal.
This can be an arthroscopically-assisted operation.
For many patients it is a difficult decision whether to proceed with a full resurfacing or a total hip replacement. This is best handled by a detailed discussion with the surgeon. Not all hips can be resurfaced. Sometimes very thin bones, or a very deformed hip joint, are unsuitable for the procedure. In principle, the resurfacing is best aimed at the high-activity user, or the patient who may dislocate if they undergo a more traditional total hip replacement. The time for recovery from surgery, the length of stay in hospital, and the length of time walking support is needed after operation is roughly the same for both operations. After surgery, there is no real difference between the two in terms of what a patient can do. For those in doubt, visit the page “Activities After Hip Replacement”. Each of the patients illustrated has a standard hip replacement in place. The pictures speak for themselves.