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

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 < 0.01) and no multicollinearity. In a combined model including aHKA, JLCA, MMCR and cartilage thickness difference, all four variables remained significantly associated with %MA (adjusted 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.