Magnetic resonance imaging‐based meniscal coverage and cartilage thickness are associated with mechanical axis alignment in knee osteoarthritis

Abstract Purpose This study examined whether magnetic resonance imaging (MRI)‐based meniscal and cartilage measurements explain the percentage of mechanical axis (%MA) to a degree comparable with the joint line convergence angle (JLCA) when added to the arithmetic hip–knee–ankle (aHKA) angle. The association between tibial bony alignment and medial meniscal coverage across osteoarthritis (OA) severity was also assessed. Methods This cross‐sectional study included 94 knees from 89 female patients (mean age, 54.6 years; Kellgren–Lawrence [KL] Grade 0–4). Weight‐bearing full‐leg radiographs were used to assess %MA, aHKA, the medial proximal tibial angle (MPTA) and JLCA. Three‐dimensional MRI measured medial meniscus coverage and cartilage thickness. Multiple regression compared the contributions of JLCA and MRI‐based measurements when each was added to aHKA. The MPTA‐by‐OA‐severity interaction was analyzed. Results MPTA was significantly correlated with the medial meniscus coverage ratio (MMCR) in knees with advanced OA (KL Grade 3–4; r  = 0.404) but not with mild or no OA (KL Grade 0–2; r  = 0.064), whereas the MPTA‐by‐severity interaction was not significant ( p  = 0.116). Model A explained 67% of the %MA variance (adjusted R 2  = 0.668). Adding JLCA improved model fit (Model B: adjusted R 2  = 0.840). Adding MMCR and the height‐normalized medial‐to‐lateral cartilage thickness difference to aHKA achieved a comparable model fit (Model C: adjusted R 2  = 0.841), with all predictors significant ( p  R 2  = 0.864). Conclusion Bony alignment and MRI‐based intra‐articular structural measurements were associated with weight‐bearing mechanical axis alignment in knee OA. When added to aHKA, MRI‐based meniscal coverage and cartilage thickness explained %MA with a model fit comparable to that obtained by adding JLCA. Thus, MRI‐based measurements may add complementary structural information to conventional radiographic evaluation. Level of Evidence Level III, cross‐sectional study.