Do survival rate and serum ion concentrations 10 years after metal-on-metal hip resurfacing provide evidence for continued use?

BACKGROUND: Owing to concerns attributable to problems associated with metal-on-metal bearing surfaces, current evidence for the use of hip resurfacing is unclear. Survival rates reported from registries and individual studies are controversial and the limited long-term studies do not conclusively allow one to judge whether hip resurfacing is still a reasonable alternative to conventional THA.

QUESTIONS/PURPOSES: We asked whether the long-term survival rate of hip resurfacing is comparable to that of conventional THA and certain factors can be identified that influence serum ion concentration 10 years postoperatively. We specifically assessed (1) the 10-year survivorship in the whole cohort and in male and female patients, (2) serum concentrations of metal ions in patients with hip resurfacing who had not undergone revision surgery, and (3) potential influencing factors on the serum ion concentration.

METHODS: We retrospectively reviewed our first 95 patients who had 100 hip resurfacings performed from 1998 to 2001. The median age of the patients at surgery was 52 years (range, 28-69 years); 49% were men. We assessed the survival rate (revision for any reason as the end point), radiographic changes, and serum ion concentrations for cobalt, chromium, and molybdenum. The correlations between serum ion concentration and patient-related factors (age, sex, BMI, activity) and implant-related factors (implant size, cup inclination, stem-shaft angle) were investigated. The minimum followup was 9.3 years (mean, 10 years; range, 9.3-10.5 years).

RESULTS: The 10-year survivorship was 88% for the total cohort. The overall survival rate was greater in men (93%) than in women (84%). Median serum ion levels were 1.9 μg/L for chromium, 1.3 μg/L for cobalt, and 1.6 μg/L for molybdenum. Radiolucent lines around acetabular implants were observed in 4% and femoral neck thinning in 5%.

CONCLUSIONS: Although our overall failure rate was greater than anticipated, the relatively low serum ion levels and no revisions for pseudotumors in young male patients up to 10 years postoperatively provide some evidence of the suitability of hip resurfacing in this subgroup.

LEVEL OF EVIDENCE: Level IV, therapeutic study. See the Instructions for Authors for a complete description of levels of evidence.