Obesity Is Preferentially Associated With Patellofemoral Compartment Wear: A Magnetic Resonance Imaging Assessment

BACKGROUND: A well-known association exists between obesity and knee osteoarthritis (OA) for both incidence and progression of the disease. However, the cartilage wear patterns in OA associated with obesity are less well studied. METHODS: The OA initiative, a prospective sample of 4,796 patients, was used for this study. After the application of inclusion and exclusion criteria, patients were stratified into increasing body mass index (BMI) cohorts (BMI < 25, 25 ≤ BMI < 30, 30 ≤ BMI < 40, and 40 ≤ BMI). Knee MRIs were assessed using the semiquantitative MRI Osteoarthritis Knee Score scores. Patellofemoral (PF), medial, and lateral compartment cartilage scores were compared among BMI cohorts, controlling for confounders using linear regression models. RESULTS: In total, 2,006 patients were present in our cohort, 773 men (38.5%) and 1,233 women (61.5%); the mean age was 61.7 ± 8.9 years. Increasing BMI was independently associated with increasing grades of PF wear for both right and left knees in the lateral patella facet (right knee β: 0.208, 95% confidence interval [CI]: 0.128 to 0.288, P < 0.001, left knee β: 0.147, 95% CI: 0.056 to 0.237, P = 0.002), medial femoral trochlea (right knee β: 0.135, 95% CI: 0.065 to 0.204, P < 0.001, left knee β: 0.142, 95% CI: 0.063 to 0.221, P < 0.001), and lateral femoral trochlea (right knee β: 0.163, 95% CI: 0.093 to 0.232, P < 0.001, left knee β: 0.147, 95% CI: 0.067 to 0.226, P < 0.001). For the right knee, increasing BMI was associated with medial compartment wear in the posterior femoral area (β: 0.070, 95% CI: 0.015 to 0.126, P = 0.013) and lateral compartment wear in the central tibial area (β: 0.070, 95% CI: 0.002 to 0.138, P = 0.045). For the left knee, increasing BMI was associated with medial compartment wear in the central femoral area (β: 0.093, 95% CI: 0.016 to 0.171, P = 0.018). DISCUSSION: Obesity is preferentially associated with increasing cartilage wear in the PF compartment in comparison to the tibiofemoral compartment. Physical therapy and exercise programs that promote weight loss should be modified to decrease forces on the PF joint.