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High rate of adverse events found with metal-on-metal total hip arthroplasty
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The rate of adverse events, such as pseudotumor formation, high metal ion levels and metallosis, caused by metal-on-metal total hip arthroplasties is higher than research previously indicated.
“Our study shows a substantially higher incidence of pseudotumor formation and subsequent revisions in patients with [metal-on-metal] MoM total hip arthroplasties than previously reported,” Bart H. Bosker, MD, a researcher in the department of orthopedic surgery at the Isala Clinics, The Netherlands, said during his presentation at the 12th EFORT Congress 2011.
For their study, Bosker and colleagues evaluated a prospective cohort of asymptomatic patients to determine the incidence of symptomatic pseudotumors after large-diameter femoral head MoM total hip arthroplasty (THA) and to identify potential risk factors for this condition.
Bosker noted that the results of the study came after an April 2010 alert issued by the British Orthopaedic Association regarding adverse events following MoM THAs.
Adverse events evaluated
From January 2005 through November 2007, Bosker and colleagues conducted a study of 108 patients who had large-size femoral head MoM THAs performed at a single center. The investigators collected patient data on pain and mechanical symptoms, hip outcome scores, SF-36 scores and metal-ion levels. They also performed physical examinations, and took conventional hip and pelvis X-rays and CT scans. Patients who had CT scans with suspected peri-articular masses were evaluated by MRI, ultrasound biopsies and histological tests.
Overall, the study group had an average follow-up of 3.6 years.
The investigators found that 42 patients were diagnosed with pseudotumors. Thirteen patients with a symptomatic pseudotumor underwent revision arthroplasty, which included a polyethylene acetabular component with a small-diameter metal head. The total revision rate was 12%.
“We did not anticipate the high incidence of pseudotumor formation. Most revision cases were identified only after applying an intensive screening protocol,” Bosker told Orthopedics Today. “We recommend close monitoring of patients with a MoM hip arthroplasty.”
In addition, the researchers found that patients with elevated metal ions displayed a four times higher risk of developing a pseudotumor. The investigators did not find a difference in clinical outcome scores among those with a tumor compared to those without a tumor, and did not identify any relation with head size or component orientation.
Change in protocol
Based on these study results, Bosker said that all large, femoral head MoM hip arthroplasties at his institution are being evaluated through an intensive screening protocol, and use of these components during THA has been discontinued. Patients will also have regular follow-up assessments.
“We advise close monitoring of all patients treated with MoM total hip arthroplasties,” he said. – by Tara Grassia
Reference:
- Bosker BH, Ettema HB, Boomsma MF, et al. Incidence of pseudotumors in patients after metal-on-metal large-diameter femoral head total hip arthroplasty: A prospective cohort study. Paper presented at the 12th EFORT Congress 2011. June 1-4. Copenhagen.
- Bart H. Bosker, MD, can be reached at the Department of Orthopaedic Surgery, Islala Clinics, Postbus 10500, 800GM, Zwolle, The Netherlands ; 0031-6-24866058; fax: 0031-50-5340373; email: b.h.bosker@isala.nl.
- Disclosure: Bosker has no relevant financial disclosures.