Background
and purpose — Metal-on-metal (MoM) total hip arthroplasty (THA) and hip
resurfacing arthroplasty (HRA) have been widely used during the early
21st century. We assessed the midterm risk of cancer of patients treated
with modern MoM hip implants compared with patients with non-MoM hip
implants and the general Finnish population with special interest in
soft tissue sarcomas and basalioma due to the findings of our previous
report.

Patients
and methods — All large-diameter head MoM THAs and hip resurfacings
performed in Finland between 2001 and 2010 were extracted from the
Finnish Arthroplasty Register (10,728 patients). Patients who underwent
conventional THA formed the non-MoM reference cohort (18,235 patients).
Data on cancer cases up to 2014 were extracted from the Finnish Cancer
Registry. The relative risk of cancer in the general population was
expressed as the ratio of observed to expected number of cases, i.e.,
standardized incidence ratio (SIR). Poisson regression analysis was used
to compare the cancer risk between the cohorts. The mean follow-up was
7.4 years (1–14) in the MoM cohort and 8.4 years (1–14) in the non-MoM
cohort.

Results
— The overall risk of cancer in the MoM cohort was comparable to the
general Finnish population (SIR 0.9, 95% CI 0.9–1.0). Risk of basalioma
in the MoM cohort was higher than in the general Finnish population (SIR
1.2, CI 1.1–1.4) and higher than in the non-MoM cohort in the
stratified regression analysis (RR 1.2, CI 1.0–1.4, p = 0.02). The SIR
of soft-tissue sarcoma in the MoM cohort was 1.4 (CI 0.6–2.8); the
incidence was same as in the non-MoM cohort.

Interpretation
— Metal-on-metal hip implants are not associated with an increased
overall risk of cancer during midterm follow-up.