The purpose of this population-based study was to determine the association between morbid obesity and 10-year mortality and complications in patients undergoing primary THA.

A cohort study of 22,251 patients, aged 45–74 years old, treated with primary THA between 2002 and 2007 for osteoarthritis, was conducted using Ontario administrative healthcare databases. Patients were followed for 10 years. Risk ratios (RRs) of mortality, reoperation, revision, and dislocation in patients with body mass index (BMI) > 45 kg/m2(morbidly obese patients) compared with BMI ≤45 kg/m2 (non-morbidly obese) were estimated.

3.3% of the cohort (726) was morbidly obese. Morbidly obese patients were younger (mean age 60.6 vs. 63.3, P-value < 0 .001) and more likely to be female (63.9% vs. 52.2%, P-value < 0 .001), compared with non-morbidly obese patients. Morbid obesity was associated with higher 10-year risk of death (RR 1.38, 95% CI 1.18, 1.62). Risks of revision (RR 1.43, 95% CI 0.96, 2.13) and dislocation (RR 2.38, 95% CI 1.38, 4.10) were higher in morbidly obese men, compared with non-morbidly obese men, there were no associations between obesity and revision or dislocation in women. Risk of reoperation was higher in morbidly obese women, compared to non-morbidly obese women (RR 1.60, 95% CI 1.05, 2.40), there was no association between obesity and reoperation in men.

Morbidly obese patients undergoing primary THA are at higher risks of long-term mortality and complications. There were differences in complication risk by sex. Results should inform evidence-based perioperative counseling of morbidly obese patients considering THA.