Long-term study confirms superiority of cross-linked polyethylene in hip implants

Hip implant x-rayA 16-year study comparing hip implants using conventional polyethylene (CPE) with cross-linked polyethylene (XLPE) confirms that the latter results in lower wear rates and a reduction in bone lysis, or loss. The study, conducted by Australian Orthopaedic Association National Joint Replacement Registry professor Richard de Steiger and fellow researchers, was published in the Journal of Bone and Joint Surgery on Aug. 1.

“Total hip arthroplasty (THA) is an effective operation for the management of end-stage hip osteoarthritis, but long-term success can be limited by wear of the polyethylene bearing surface,” write de Steiger and his colleagues. “The use of XLPE has resulted in a significant reduction in the rate of revision at 16 years following THA for osteoarthritis. This evidence suggests that the longevity of THA is likely to be improved, which may enable younger patients to undergo surgery.”

The number of THA procedures has been increasing, note the authors, and this is expected to continue. Non-cross-linked, ultrahigh-molecular-weight polyethylene has been used for more than 50 years in this procedure, but it has a limited lifespan. Although laboratory and clinical studies of XLPE from various manufacturers have shown a reduction in wear compared with the conventional material, “the follow up was not long enough to show a difference in the rates of revision surgery, which ultimately is most important for the patient,” said the paper. The study remedied this by using data from a national joint replacement registry to compare the rate of revision at 16 years after THA for osteoarthritis between patients who had received XLPE and those treated with CPE.

The study included more than 240,000 patients with hip osteoarthritis who underwent a THA procedure in Australia between 1999 and 2016. Outcomes were analyzed according to the type of bearing surface used in the hip implant. Implants with an XLPE bearing surface were used in approximately 199,000 procedures, while implants with CPE bearings were used in 41,000 procedures.

As early as six months after hip replacement, revision rates were substantially lower in patients with XLPE bearings. Over 16 years, the cumulative rate of revision surgery was 11.7% in the CPE group compared to 6.2% in the XPLE group.

The study showed that the use of XLPE makes THA—already one of the most effective operations—even better, write the authors. “The use of XLPE has improved the outcomes of THA at 16 years with no observed untoward effects. The evidence derived from our study suggests that the longevity of THA with XLPE is likely to be improved, compared with that of THA with CPE, beyond 16 years and may enable younger patients to undergo THA confident of a reduced need for revision in the long term.

"Wear-related and implant-longevity issues are particularly important in younger patients, who are generally more active and have a longer life span than their older counterparts," Prof. de Steiger and colleagues concluded.

"We believe that the evidence of reduced long-term wear with XLPE is now so strong that, when a polyethylene bearing surface is used in THA, it should be XLPE, particularly in younger patients."