Objective: Bone marrow lesions are associated with pain and compartment-specific progression of joint space narrowing in patients with knee osteoarthritis (OA). Bone marrow lesions occur in regions under increased loading, and excess loading produces increased bone mineral density (BMD). The ratio of BMD in the medial tibial plateau compared with that in the lateral tibial plateau (M:L BMD ratio) reflects loading in the knee. Therefore, we hypothesized that a higher M:L BMD ratio would be associated with medial bone marrow lesions, and that lower ratios would be associated with lateral bone marrow lesions.
Methods: Participants in the Framingham Osteoarthritis Study underwent magnetic resonance imaging (MRI), measurement of bone mineral density (BMD), and knee radiography between 2002 and 2004. MRI was used to define medial and lateral bone marrow lesions in the medial and lateral tibiofemoral compartments, respectively. We performed a logistic regression analysis with medial bone marrow lesions as the outcome, testing M:L BMD ratio groups as predictor variables. We adjusted for age, sex, body mass index, and systemic BMD, using generalized estimating equations to adjust for correlations between knees. An identical analysis evaluating lateral bone marrow lesions was performed.
Results: Medial bone marrow lesions were strongly associated with a high M:L BMD ratio. The odds ratios (ORs) for prevalent medial bone marrow lesions, for the lowest to the highest quartile of M:L BMD ratios, were 1.0 (referent), 1.3, 5.0, and infinity (P for trend < 0.0001). Lateral bone marrow lesions were strongly associated with low M:L BMD ratios (the ORs for prevalent lateral bone marrow lesions, for the highest to the lowest quartile, were 1.0 [referent], 3.0, 26.8, and 54.0 [P for trend < 0.0001]).
Conclusion: Medial bone marrow lesions occur in knees with relatively higher local medial tibial bone density, and lateral bone marrow lesions occur in knees with relatively higher lateral tibial bone density, supporting the hypothesis that local BMD reflects loading within the knee. Our findings emphasize the importance of loading in the pathophysiology of OA.