Comparison of anatomical risk factors for noncontact anterior cruciate ligament injury using magnetic resonance imaging.

Purpose: To compare the significance of the tibio-femoral geometrical indices (notch width index, medial and lateral tibial slopes) and patellar tendon- tibial shaft angle in predicting non-contact ACL injuries and to compare these factors between genders.

Methods: Retrospective case control study evaluating 66 MRI knee of patients of age group of 18-60 years with 33 cases of noncontact ACL injury and 33 age matched controls. Notch width index, medial and lateral tibial slopes and patellar tendon tibial shaft angles were calculated and compared for statistical significance and was also compared between the genders. ROC curve was for plotted for the significant factors.

Results: Statistically significant difference was seen in notch width index and patellar tendon tibial shaft angles with cases showing a narrow notch width index and an increased patellar tendon tibial shaft angle. Gender comparative results showed no statistically significant differences. ROC curve plotted for NWI showed an optimal cut off value of 0.263 with a sensitivity of 88% and a specificity of 52%. ROC curve plotted for PTTS angle showed a cut off value of 26.7 degrees with a sensitivity of 67% and a specificity of 49%.

Conclusion: Narrow Notch width index and increased Patellar tendon tibial shaft angle are predictors of ACL injury. PTTS angle which has been studied as a function of knee flexion angle, can itself be an independent predictor of ACL injury (at a constant knee flexion angle).