BMI independently predicts younger age at hip and knee replacement.

Obesity has been identified as a risk factor for the development of hip and knee osteoarthritis (OA) and may play a role in exacerbating existing disease. Therefore, we hypothesized that obese patients would present for hip and knee replacement surgery at a younger age than nonobese patients. From our registry, we performed a cross-sectional study of 841 hip and 804 knee replacement patients. Patients were categorized by BMI ≤ 25 kg/m(2), 25.1-29.9 kg/m(2), 30-34.9 kg/m(2), and ≥ 35 kg/m(2). Linear regression modeling was used to examine the relationship between BMI and age at surgery. Hip and knee replacement patients' mean age at surgery was 7.1 and 7.9 years younger, respectively, if their BMI was ≥ 35 kg/m(2) when compared to patients with a BMI ≤ 25 kg/m(2) (P = 0.002). BMI was a significant independent (of gender, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score, surgeon, and comorbidity) predictor of age at knee replacement (P < 0.05). WOMAC scores were significantly worse preoperatively in patients with a BMI ≥ 35 kg/m(2) compared to those with a BMI ≤ 25 kg/m(2) (P < 0.05). Our study indicates that obese patients, especially those with a BMI ≥ 35 kg/m(2), presented for and underwent joint replacement surgery at a younger age as compared to nonobese patients.