Body mass index, pain and function in individuals with knee osteoarthritis

BACKGROUND: Obesity is a risk factor for progression of knee osteoarthritis (OA), and high body mass index (BMI) may interfere with treatment effectiveness on pain and function in individuals with knee OA. This study investigated the effects of BMI on pain and function during a four-week exercise programme in patients with knee OA. MATERIALS AND METHODS: Forty-six (31 women and 15 men) participants with knee OA of different BMI categories (15 normal weight participants, 13 over weight participants and 18 obese participants), received standardised exercise therapy programme twice a week for 4 weeks. Outcome included a 10-point pain rating scale for pain-intensity and the western Ontario and McMaster university osteoarthritis index (WOMAC) for physical function. RESULTS: Two-way repeated measure analysis of variance (ANOVA) on pain assessment score revealed a significant effect of time (F = 1049.401, P < 0.001) and group (F = 9.393, P < 0.001) on pain. Similar significant effect of time (F = 595.744, P < 0.001) and group (F = 5.431, P = 0.008) was obtained for WOMAC score on function. Post hoc analysis revealed significant difference between the normal weight and overweight group (t = 2.472, P = 0.016) and between normal weight and obese group (t = 3.893, P = 0.005) on pain outcome at the 4(th) week post treatment. No significant difference was found at 4(th) week post treatment on WOMAC scores (F = 2.010, P = 0.146). CONCLUSION: Exercise improved pain and function scores in OA patients across the BMI groups. Overweight independent of obesity may interfere with effectiveness of pain control during the symptomatic treatment of knee OA patients.