BMI and Varus Malalignment Compound to Define a High-Risk Phenotype for Compartment-Specific Knee Osteoarthritis Progression

In 3,191 Osteoarthritis Initiative participants, BMI and varus malalignment jointly predict greater medial compartment cartilage thinning, with interaction effects of beta=0.0016 mm/year (femur) and beta=0.0018 mm/year (tibia) per 1-SD BMI×1-SD HKA.

• Why it matters: It remains unclear which individuals with knee osteoarthritis will show structural decline, and whether BMI and alignment act independently or together across knee compartments.
• What they did: Using 5,930 limbs followed 0–60 months, the study quantified medial and lateral cartilage thickness and modeled longitudinal change with linear mixed-effects interactions with time, adjusting for age, sex, and baseline Kellgren-Lawrence grade.
• The result: Lateral cartilage loss was linked to alignment but not BMI, while TKR odds rose with absolute HKA deviation (1.11-fold at five years; 1.14-fold at ten years per 1-degree), and the medial BMI×varus interaction identifies a high-risk phenotype for medial progression.

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