Surface Replacement of the Hip

Touted as the latest advance in replacement surgery, Hip resurfacing has caught the eye of patients and doctors alike. Advantages include a less complex surgery, shorter operative time, lesser patient morbidity and a "more anatomical replacement". This surgery enables patients to return to a more active lifestyle and is hence useful to younger patients. Patients requirements include younger age, good bone stock and expectation of return to an active lifestyle.

Surface replacement of the hip entails replacing the weight bearing area of the head of the femur and providing a "cap" for it in the acetabulum. A more comprehensive surgery involving removal of the proximal portion of the femur is avoided and this enables the patient to return to normal activities much earlier than with traditional hip replacement surgery.

Due to the complexity and need for perfect positioning of the implant, special training is required and at present there are only a few centers in India providing this surgery.

What is Hip Resurfacing

A total hip replacement is the standard operation for an osteoarthritic hip. During a hip replacement the head and neck of the femur are removed. A cavity 15-20 cm long is then made in the shaft of the femur and a metal stem inserted. A cup is then placed into the socket which has been reamed to shape. Both components are held in place by either bone in-growth or with polymer cement. In hip resurfacing, the hip joint is relined rather than replaced. The head and neck of the femur are preserved. The worn surfaces of the head and socket are carefully machined away with precision instruments. The joint is then lined with a metal covering for the head and socket.

What Implants are used for hip resurfacing?
The implant is made of high carbon Cobalt Chromium, a metal alloy consisting primarily of the elements cobalt, chromium but nickel and molybdenum. It is used for its strength, resistance to wear, and its biocompatibility, which means that it does not normally create adverse effects inside the body.

What are the advantages of hip resurfacing?

The hip resurfacing implant has three key advantages:
* Bone conservation
* Low wear bearing
* Anatomic sized bearing

Conservation of Bone

One of the major problems of revision hip surgery (where a worn out or loose hip implant has to be changed to another one) is the loss of bone which necessitates the use of larger and longer hip stems. In hip resurfacing the head and neck are preserved. Only the worn surface and 4 mm of bone below it are removed. This allows the patients to keep as much of their own hip as possible for as long as possible. Therefore if the resurfacing should fail for any reason the head and neck can be removed and a standard total hip replacement can be performed.

Low Wear and Low Friction Bearings

One of the major advantages of hip resurfacing is the metal-on-metal bearing. The precision-engineered components are made of a hard, biocompatible alloy (which consists mainly of cobalt and chromium) which produces very low rates of wear. The surface finish (the smoothness of the shiny metal surfaces) is controlled to around five microns. One micron is one thousandth of a millimetre or 0.00004 of an inch. The average width of a human hair is around 85 to 100 microns, so the smoothness of the resurfacing bearing surface is controlled to about 1/20th the width of a human hair.

Anatomically Sized Bearings

In a resurfaced hip the femoral head is similar in size to the natural hip. In conventional total hip replacement the average head size is smaller than the natural hip. The advantage of a larger head size is a greater range of movement of the hip and increased stability, in other words less chance of it coming out of joint (dislocating). The sphericity (or “roundness”) of the bearing surfaces is also critical, so there is a deliberate mismatch between the diameters of the head and cup bearing surfaces, allowing body fluid to enter the bearing and lubricate it, just as it does in the normal hip joint.

How different is the Operation for a Hip resurfacing from one for a conventional hip replacement?

In general your treatment will progress along the usual stages for a conventional hip replacement. Preliminary tests will be needed a few weeks in advance of the surgery to determine whether you are ready for surgery and whether any special precautions may be required. The risk associated with hip resurfacing surgery and the ensuing complications are similar to that of a conventional operation. The incision for a hip surface replacement may be little longer than that required for a conventional hip joint replacement although the procedure typically takes a similar amount of time. In most cases, the post-surgery recovery time is shorter than for a conventional hip replacement. In the first few weeks after the operation, you will take part in a rehabilitation programme. You will be advised on post-surgery activities by your orthopaedic surgeon but usually patients will be able to climb stairs again soon with the use of a walking aid. Generally speaking, you should be relatively independent after about 1 and 1/2 months and, about 3 months after surgery, most patients return to everyday activities. Many patients consider themselves cured after about one year.


Is my hip suitable for Resurfacing?

This is dependant on your age, medical conditions and the X-rays of your hip. Your orthopaedic surgeon will advise you as to whether your hip can be resurfaced.