Associations of the hip–knee–ankle angle and joint line convergence angle with medial meniscal extrusion

Aim: To examine the associations of the hip–knee–ankle angle (HKAA) and the joint line convergence angle (JLCA) with medial meniscal extrusion (MME). In addition, we aimed to determine their independent associations after adjusting for osteoarthritis severity and meniscal tear characteristics.

Materials and Methods: This single-center retrospective cross-sectional study included knees from patients aged ≥ 40 years with available full-length lower-limb radiographs and knee magnetic resonance imaging (MRI). Knees with HKAA ≥ -2° were included; varus alignment was recorded as positive and valgus alignment as negative. Radiographic alignment parameters, osteoarthritis severity, MME, and meniscal tear characteristics were recorded. Hierarchical multivariable regression was used to evaluate the independent associations of HKAA and JLCA with MME. Within-patient clustering was accounted for using generalized estimating equations.

Results: A total of 175 knees from 129 patients were analyzed. Mean HKAA was 4.66 ± 3.61°, mean JLCA was 2.09 ± 1.71°, and mean MME was 2.54 ± 1.96 mm. The covariate model explained 61.2% of the variance in MME (adjusted R² = 0.599). Adding HKAA increased the explained variance (ΔR² = 0.037), and adding JLCA on top of HKAA provided modest additional explanatory value (ΔR² = 0.010). In the fully adjusted generalized estimating equations (GEE) model, both HKAA (unstandardized coefficient, B = 0.077 mm/°; 95% CI 0.008 – 0.145; p = 0.028) and JLCA (B = 0.156 mm/°; 95% CI 0.008 – 0.305; p = 0.039) were independently and positively associated with MME.

Conclusion: MME is independently associated with coronal knee alignment. While HKAA appears to be the dominant alignment parameter, JLCA provides additional information beyond the mechanical axis. Clinical interpretation of MME should consider global mechanical alignment, JLCA, and posterior root integrity together.