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 were hindered bys 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 reintroduced 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. This is the longest serving hip resurfacing device with the longest pedigree on the market today.
The resurfacing procedure has been somewhat tarnished by copy implants which through various design changes (in most cases very well meaning) managed to reduce the success of the procedure. The Birmingham has remained true to its original design and has remained the implant of choice with the best results in the National Joint registry for resurfacing devices.
Over the years the procedure has morphed from being performed in over 10% of the population, to an operation which we reserve for a small niche of patients and go through a very careful selection and counselling process prior to its use. Generally it is reserved for young (elderly have a higher failure rate), male (female patients have an even higher failure rate- this is national guidance) and active patients who would benefit from its functional outcomes and resistance to dislocation. I am happy to discuss in detail and at length the various risks and benefits of the device for each and every patient considering it as an option.
Benefits of Hip Resurfacing
Hip resurfacing provides a bearing of similar size to the patient’s own hip. This reduces dislocation rates and patients report the hip feels more ‘normal’. This may also be due to the fact that surgeons don’t ‘instrument’ the femur as with a normal hip replacement, thereby reducing the tissue damage and inflammatory substances released.
Resurfacing patients often report a quicker post-operative recovery in the short term, 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 rise for certain patient groups. Active males with osteoarthritis of the hip are most suitable for this treatment 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. Females have reduced bone mass which worsens after hormonal changes post-menopause. They also have smaller hip sizes. This has important ramifications for the lubrication within the hip, and therefore rates of wear.
The Hip Resurfacing Procedure
The approach varies, but the majority of orthopaedic hip surgeons, Mr Eastaugh-Waring included, use a posterior approach to the hip. This 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 it is necessary to 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 reshaped and a metal cap applied with or without cement.
Post-operatively, most patients will be able to fully weight bear the following day. Discharge from hospital is usually within three to five days.
Complications in Hip Resurfacing Treatments
Most large series report an early failure rate of resurfacing at around two to four per cent. 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 it 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, analysing over a thousand hip resurfacings, reported ALVAL in 0.5% in young males, but up to 25% in females. Causes are uncertain, but may relate to the smaller hip size and less than optimal lubricating regime. Stephen opts to use a large ceramic bearing in female patients for this reason.
If you wish to book an appointment to discuss hip resurfacing treatments please get in touch via the contact page.