Effect of chronic anterior cruciate ligament deficiency on patellofemoral alignment: A comparative study

Objectives: Chronic anterior cruciate ligament (ACL) deficiency changes knee biomechanics and may negatively impact patellofemoral alignment, leading to early degenerative changes. We evaluated radiological alterations in patellofemoral alignment between knees with chronic unilateral ACL deficiency and the healthy contralateral knee. Materials and Methods: This comparative study involved eighty patients aged 18–50 years with magnetic resonance imaging-confirmed unilateral ACL tears of more than 6 months. Clinical assessment included tests: Lachman, Pivot Shift, McMurray, Varus-Valgus stress, and J-sign. Radiological evaluation compared the injured and contralateral knees using the Insall-Salvati ratio, Caton-Deschamps Index (CDI), Merchant congruence angle, Laurin’s angle, and Kellgren-Lawrence (K-L) grading. In addition, a subgroup analysis was conducted to distinguish sports-related from non-sports-related injuries. Results: The average age was 28.38 ± 8.34 years, with 75% of injuries stemming from sports activities. The Merchant congruence angle was notably higher in injured knees compared to the contralateral side (12.70 ± 1.24° vs. 5.90 ± 1.57°, p < 0.001), whereas Laurin’s angle was significantly lower (8.25 ± 1.21° vs. 10.95 ± 1.64°, p < 0.001), suggesting lateral patellar malalignment. No significant differences were detected in the Insall-Salvati ratio or the CDI. Early osteoarthritic changes (K-L Grade 1) were observed in 25% of the injured knees, while all contralateral knees were graded as Grade 0. Conclusion: Chronic ACL deficiency is linked to notable patellofemoral malalignment, marked by increased lateral displacement and tilt of the patella, while patellar height remains largely unaffected. Conducting early radiological evaluations of patellofemoral alignment can support prompt intervention and potentially enhance long-term knee health.