OBJECTIVE: The relationship between metal wear debris, pseudotumor formation and metal hypersensitivity is complex and not completely understood. The purpose of this study was to assess the prevalence of pseudotumor formation in a consecutive series of metal-on-metal (MoM) total hip arthroplasty (THA) and to investigate its relationship to serum metal-ion levels and hypersensitivity to metal.

METHODS: Forty-one patients (31 males), mean age 52 (28-68) years, with a total of 49 large-head MoM THA participated in a 5-7-year follow-up study. Patients underwent ultrasonography, serum metal-ion concentrations were measured, metal allergy and atopic dermatitis were evaluated, and the questionnaires of the Oxford Hip Score (OHS), Harris Hip Score (HHS) and the Short-Form Health Survey (SF-36) were completed.

RESULTS: Pseudotumors were found in eight patients, but they were asymptomatic and their serum metal-ion levels were similar to those observed in patients with no pseudotumors (p > 0.36). The capsule-stem distance of mean 8.6 mm (SD 3.82, 95% CI: 5.40-11.79) was wider (p = 0.02) in patients with pseudotumours than in patients without pseudotumors of mean 5.6 mm (SD 2.89, 95% CI: 4.68-6.58). Positive patch test reactions were seen in three patients. Higher serum metal-ion levels of chromium and cobalt were significantly correlated with steeper cup inclination and smaller femoral head sizes, and were associated with female gender (p < 0.04).

CONCLUSION: We found no association between pseudotumor formation, serum metal-ion levels, metal patch test reactivity, and atopic dermatitis. However, clinicians should be aware of asymptomatic pseudotumors, and we advise further exploration into the mechanisms involved in the pathogenesis of pseudotumors.