The problems with Metal on Metal Hip Implants

Total hip replacement is one of the most successful operations and is currently performed in 70,000 patients a year in the UK, 250,000 in the United States and 1,000,000 worldwide.

In an attempt to improve wear resistance and to allow bone conservation through hip resurfacing, metal on metal bearings were reintroduced in the 1990’s. They are made of cobalt chromium alloys, and in some serious cases metal hip resurfacing has shown excellent results in younger and most active patient groups.

Problems with hip resurfacing that were initially reported included raised blood cobalt and chromium ions, loosening of components, hip fracture and soft tissue reactions around the hip. In an attempt to overcome the fracture problems and to extend the use of large diameter metal on metal bearings to those not suitable for hip resurfacing, metal resurfacing type bearings were introduced on total hip replacement stems. These large diameter metal on metal hip replacements had a lower rate if dislocation. In fact, metal on metal bearings were used in up to 35% of all total hip replacements in the US in 2009.

What are the adverse symptoms?

The most common symptoms of adverse reactions to metal debris are pain, swelling around the hip and loss of function with a reduced exercise tolerance. Soft tissue swelling may be noticed in the groin and buttocks. Pain and symptoms in patients with metal on metal hip implants should be investigated and referred to an orthopaedic surgeon. Full clinical assessments should be carried out together with radiographs, full blood counts and C-reactive protein. MRI scanning should be done. Hip aspiration and injections may also be helpful.

Bloods should be taken for cobalt and chromium ion measurements and again this is best done as part of an orthopaedic assessment. In patients with no symptoms levels of these ions are typically around two parts per billion. It is suggested that patients with levels of cobalt or chromium ions above seven parts per billion should be further investigated and ion measurements repeated as part of closer follow up. There is evidence that levels are higher in the first 6-12 months after insertion of a metal on metal bearing as it beds in.

As of yet the level of cobalt or chromium at which revision surgery is advised has not been clearly defined. It is agreed that revision surgery should be performed in patients with substantial pain, worsening pain, limp or poor function. Similarly it should also be considered in those patients with rising blood metal ions, increasing fluid collections or masses of  fluid collections around the hip.

What is the Risk to Patients?

The risk to patients of failing metal on metal hip implants is a progressive inflammatory response leading to tissue necrosis around the hip. All joint replacements using conventional bearings of metal on polythene, ceramic on polythene or ceramic on ceramic will wear and may fail with debris generating different adverse responses. These can include metalosis loosening and dislocation. The difference with metal on metal bearings seems to be the potential to develop necrosis and cell death in tissues around the hip. They can occur with all metal on metal bearings in both hip resurfacing and total hip replacements. They are more likely in women. If a painful metal on metal hip is revised before substantial soft tissue damage then the outcome is likely to be excellent.

If I Have No Pain in my Hip – What Should I Do?

In the absence of pain in a metal on metal bearing, no investigations are needed other than an annual assessment and the prompt reporting of new symptoms. The MHRA in the UK guidelines include four situations in which to test blood for metal ions, pain or symptoms associated metal on metal bearings, radiological features associated with adverse outcomes including component position, concerns of the patient or surgeon about the bearing and concerns about patients with higher than expected rates of failure.

The MHRA has suggested follow up for 5 years for all metal on metal implants and for the life of the prosthesis with the withdrawn ASR /ASRXL devices. Patients who have painful metal on metal implants should be reviewed by their orthopaedic surgical team. The decision on whether to revise the hip remains a clinical one between the patient and their surgeon. Currently the advice of many British orthopaedic surgeons is that large diameter metal on metal total hip replacement should not be performed until more is known about their mode of failure with the exception of exceptional circumstances.

Hip resurfacing with components that have proven track records still seem to be in effective and safe treatment in the truly active under 55 age group.

If you received a DePuy ASR hip implant device and are having symptoms as described above please contact Liam Moloney, Solicitor Naas  at 045 898000 to find out about your rights to compensation or simply log onto our website at www.moloneysolicitors.ie