The objective of our study was to determine whether waist circumference (WC) is a more reliable indicator than body mass index (BMI) of the presence of knee osteoarthritis in obese subjects.
We performed an observational study of obese patients with no other risk factors for knee osteoarthritis. For each patient, we evaluated BMI, WC, duration of obesity and knee pain. Two groups were identified: "asymptomatic patients" (AG), without knee pain, and "symptomatic patients" (SG). For the SG, we measured pain intensity (visual analog scale [VAS], 0-100 mm) and functional repercussions (using the Lequesne and WOMAC indexes). Patients with knee pain underwent standard radiographic procedures to search for signs of osteoarthritis, and the SG was divided into two subgroups: with radiological signs of osteoarthritis (SG-1) and without radiological signs of osteoarthritis (SG-2). The AG and SG groups and SG-1 and SG-2 groups were compared for age, sex, and duration of obesity. Comparisons of BMI, WC, and function involved the Student's t-test.
We recruited 56 patients for the study (82.5% females; mean obesity duration (13+/-6.5 years; mean age 43.21+/-9.58 years). The mean BMI was 39.6+/-7.23 kg/m(2) and mean WC was 113+/-14.3 cm. We found 33 patients (59%) with knee pain. Independent of age, sex, duration of obesity and BMI, the SG showed more significant WC (117.27+/-14.71 cm vs. 107+/-11.75 cm for the AG, P 0.01). In the same group and independent of the already mentioned factors, the patients with radiological signs of osteoarthritis showed significant WC [122+/-15.57 cm (SG-1) vs. 108+/-6.88 cm (SG-2) (P 0.01)]. Moreover, the VAS score of pain at rest and during effort and the WOMAC and Lequesne scores were 16+/-25.7 mm, 75+/-18.3 mm, 12.3+/-8.92 and 11.5+/-5.44 (SG-1) and 7+/-18.4 mm, 70+/-19.2 mm, 5.7+/-3.05, and 6.9+/-3.79 (SG-2), respectively. The difference between SG-1 and SG-2 was significant only for the WOMAC (P=0.015) and Lequesne (P=0.026) scores.
Independent of BMI, WC appears to be a factor associated with the presence of knee pain and osteoarthritis in obese patients. Furthermore, a high WC is associated with significant functional repercussion.