Co-existing patterns of MRI lesions were differentially associated with knee pain at rest and on joint loading: a within-person knee-matched case-controls study

BACKGROUND: To assess the association of co-existing MRI lesions with knee pain at rest or on joint loading. METHODS: We included participants from Osteoarthritis Initiative whose pain score, measured by WOMAC sub-scales, differed by ≥1 point at rest (in bed at night, sitting/lying down) or on joint loading (walking, stairs) between two knees. Cartilage morphology, bone marrow lesions, meniscus extrusion, meniscus morphology, Hoffa’s synovitis and synovitis-effusion were assessed using the compartment-specific MRI Osteoarthritis Knee Score. We performed latent class analyses to identify subgroups of co-existing MRI lesions and fitted a conditional logistic regression model to examine their associations with knee pain. RESULTS: Among 130 eligible participants, we identified five subgroups of knees according to patterns of co-existing MRI lesions: I. minimal lesions; II. mild lesions; III. moderate morphological lesions; IV. moderate multiple reactive lesions; and V. severe lesions. Compared with subgroup I, the odds ratios (ORs) and 95% confidence intervals (CI) of greater pain in bed at night were 1.6 (0.3, 7.2), 2.2 (0.5, 9.5), 6.2 (1.3, 29.6) and 11.2 (2.1, 59.2) for subgroups II-V, respectively. A similar association was observed between aforementioned subgroups and pain with sitting/lying down. The ORs (95% CI) of greater pain with walking were 1.0 (reference), 1.7 (0.5, 6.1), 0.7 (0.2, 2.3), 5.0 (1.4, 18.6) and 7.9 (2.0, 31.5) for subgroup I-V, respectively. The corresponding analysis for pain on stairs showed similar results. CONCLUSIONS: Distinct patterns of co-existing MRI lesions have different implications for the pathogenesis of osteoarthritic knee pain occurring with/without joint loading.