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Metal on Metal One Third of Patients Diagnosed with Pseudotumors after Metal-on-Metal Total Hip Arthroplasty

Josephine

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One Third of Patients Diagnosed with Pseudotumors after Metal-on-Metal Total Hip Arthroplasty Paper#303
Bart Bosker, MD, Zwolle, Netherlands Antilles
Harmen B. Ettema, Zwolle, Netherlands
Martijn F. Boomsma, MD, Zwolle, Netherlands
Boudewijn Kollen, Groningen, Netherlands
Mario Maas, Amsterdam, Netherlands
Cees Verheyen, PhD, Zwolle, Netherlands


INTRODUCTION: Peri-articular tumors occur following large-size femoral head metal-on-metal resurfacing and conventional total hip replacement. Reports until now are based on symptomatic outcomes. We intended to assess the true incidence of both symptomatic and asymptomatic cases and to identify predicting factors for the development of a pseudotumor. This is a design retrospective cohort study set in a teaching hospital in the Netherlands.

METHODS: We included all patients who underwent hip arthroplasty with large-size femoral head metal-on-metal conventional prostheses in our clinic (2005-2010). We collected data on hip outcome scores, metal ion levels and conventional pelvic and hip radiographs. All patients were scheduled for CT scan examination.

RESULTS: Between January 2005 and July 2010, primary uncemented large-size femoral head total hip arthroplasties was performed in 649 patients (732 hips). A total of 671 hips in 614 patients were evaluated with a mean follow up of 2.7 years (range 1-6.5 years). Pseudotumor was diagnosed in 207 hips (31%) in 202 patients (33%). To date, 39 (6%) of these hips were revised to a polyethylene acetabular component with small diameter metal head. We identified the following risk factors for developing a pseudotumor: female gender, swelling around the hip, discomfort around the hip, clicking sensations and anterolateral surgical approach. Patients with a pseudotumor had, on average, higher levels of cobalt and chromium in serum (10 µg/l vs 4 µg/l and 8 µg/l vs 4 µg/l respectively). No difference in clinical outcome scores was detected between the pseudotumour and non-pseudotumour group. No relation with component size or orientation could be identified.

DISCUSSION AND CONCLUSION: This study showed a substantial higher incidence of pseudotumors and subsequent revisions in patients with metal on metal total hip arthroplasties than previously reported. Because most revision (27 of 39) cases were identified only after applying an intensive screening protocol, we recommend close monitoring of patients with a metal on metal hip arthroplasty.
 

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