Study finds pseudotumor formation in more than a quarter of hips with metal-on-metal bearings

After hip arthroplasty with metal-on-metal bearings, researchers from The Netherlands found pseudotumor formation occurred in 28% of hips, according to results of this recently published study.

From 2005 through 2010, 129 patients (149 hips) underwent metal-on-metal hip resurfacing arthroplasty with a metal-on-metal femoral head and acetabular shell (Birmingham Hip Resurfacing [BHR]; Smith & Nephew, Birmingham, United Kingdom) in Martinit Hospital, Groningen, The Netherlands. Four patients were lost to follow-up for a total cohort of 129 patients (143 hips).

Three patients underwent revision before the study was done and 11 patients underwent revision after the study started. Researchers collected data on patient and surgical characteristics, clinical hip outcome scores, serum metal ion levels and radiographs and patients underwent compute tomographic scan. Among the patients who had revisions, researchers histologically examined tissue samples.

Average follow-up was 41 months. Overall, researchers found a pseudotumor in 39 patients through CT. Seven patients underwent revision because of a symptomatic pseudotumor, and 10 patients with a pseudotumor presented with complaints involving groin pain and discomfort, a noticeable mass or paresthesia. Study results showed symptomatic pseudotumors were significantly larger vs. asymptomatic pseudotumors. A predictor of pseudotumor formation included a serum cobalt level of less than 85 nmol/L. At 5 years, the implant survival rate was 87.5%.

“In our opinion, patients with a symptomatic pseudotumor should have a revision, and patients with a BHR with complaints need to be screened for a pseudotumor. Serum cobalt and chromium ion levels may be used for screening, but we find CT to be the best technique for diagnosing pseudotumors,” the researchers wrote. “Further follow-up of our patients with asymptomatic pseudotumors will provide more information on whether these pseudotumors progress over time and become symptomatic.”

Disclosure: The researchers have no relevant financial disclosures.