Overview of Orthopaedic Hip Surgery

Metal on metal articulation is not a new concept, but early orthopaedic hip treatments such as those by Mckee and Farrar suffered from the unsatisfactory engineering and materials technology available at the time. In the 1990's, Derek McMinn and colleagues took a bold step in hip resurfacing and re-introduced the concept of the metal-metal articulation, releasing the McMinn resurfacing. This went through a number of design changes such as uncemented heads, etc, before the Birmingham device was settled upon, and this is the longest serving hip resurfacing device with the longest pedigree on the market today.

Benefits of Hip Resurfacing

Hip resurfacing provides a bearing which is a similar size to the patient's own hip. This reduces dislocation rates, and patients report that the hip feels more 'normal'. This may also be due to the fact that as surgeons we don't 'instrument' the femur as with a normal hip replacement, thereby reducing the tissue damage and inflammatory substances released. Resurfacing patients do often report a quicker post-operative recovery in the short term (weeks), although function at one year onwards with a modern THR is probably similar.

The metal-metal bearing surface is also more durable than the traditional polyethylene type. Hip resurfacing treatment does however have issues with regards to the release of metal ions, as described below.

Suitability for Hip Resurfacing Treatment

This is not a device for all patients, as complication rates do rise for certain patient groups. Active males with osteoarthritis of the hip are the most appropriate and seem to have the best results, with failure rates around 0.5-2% in the medium term. Unfortunately being older and being female are both relative risk factors. The female issue is both one of reduced bone mass, worsened by the hormonal changes post-menopause, but also one of smaller hip sizes. This has important ramifications for the lubrication within the hip, and therefore rates of wear. The issue of age is also one of reducing bone mass and strength which is a normal feature of aging.

The Hip Resurfacing Procedure

The approach varies, but the majority of orthopaedic hip surgeons, myself included, will use a posterior approach to the hip which preserves the muscle function of the hip joint to allow maximal function post-operatively. Hip resurfacing procedures can cause a scar that may be slightly larger than a standard hip replacement, as we must work around an intact femoral head.

The acetabulum (cup) is prepared as for a hip replacement, and an uncemented metal shell inserted with a friction fit. The worn surface of the head is then carefully removed and a metal cap applied with or without cement.

Post-operatively most will be able to fully weight bear the following day, and discharge from hospital is usually within 3 to 5 days.

Complications in Hip Resurfacing Treatments

Most large series report an early failure rate of resurfacing at around 2-4%. The commonest cause is avascular necrosis (loss of blood supply) and/or femoral neck fracture. This is remedied by the use of a large head on a stem and means the patient still has a large bearing to allow optimal function.

The second cause of failure specific to metal-metal joints is known as ALVAL (aseptic lymphocyte- derived vasculitis and associated lesions). This is as yet still unclear, and is being studied in detail, but seems to be an inflammatory reaction by the body's immune system. The condition causes ongoing pain, often steadily worsening, and can be difficult to diagnose on simple X-rays. An experienced orthopaedic hip specialist who is aware of the condition will arrange a specially designed MRI sequence and this, in association with a fluid sample from the hip replacement, should yield the diagnosis. The treatment is to replace the metal bearing with an alternative, usually ceramic.

Rates of ALVAL vary between patients. One study from Oxford, studying over a thousand hip resurfacings, reported ALVAL in 0.5% in young males, but up to 25% in young females. Causes are uncertain, but may relate to the smaller hip size and less than optimal lubricating regime. I personally prefer to use a large ceramic bearing in female patients for this reason.

If you wish to book an appointment to discuss and review hip resurfacing treatments as a suitable procedure please contact my secretary Carol Gibb on our contact and appointments page.