The Relationship Between Lateral Femoral Condyle Index and Noncontact Anterior Cruciate Ligament Rupture

PURPOSE: The purpose of this study was to examine the relationship between distal femoral morphology and noncontact anterior cruciate ligament (ACL) rupture and the differences between digital X-ray imaging systems (DR) and magnetic resonance imaging (MRI) to evaluate distal femoral morphology. METHODS: A retrospective case-control study was performed on 120 patients. Two age- and sex-matched cohorts (each n = 60) were analyzed: primary ACL ruptures and a control group consisting of isolated meniscal tears. The lateral femoral condyle index (LFCI) was measured by DR and by MRI to quantify femoral sphericity. Differences among two groups were compared, and diagnostic performance of the risk factors was assessed. In addition, differences between DR and MRI to evaluate LFCI were examined. RESULTS: The LFCI by MRI was smaller in the knees with primary ACL rupture (median, 0.71; range, 0.62–0.78) than that of the control group (median, 0.77; range, 0.66–0.85) (p < 0.01). The LFCI was also significantly smaller in the knees with primary ACL rupture (median, 0.72; range, 0.63–0.77) than that of the control group (median, 0.79; range, 0.65–0.84) (p < 0.01) by DR. A cutoff of 0.74 of MRI yielded a sensitivity of 77% and a specificity of 78% to predict an ACL rupture, and of 0.75 of DR yield a sensitivity of 87% and a specificity of 77% to predict an ACL rupture. CONCLUSION: This study showed that a decreased LFCI is associated with an ACL rupture, and both DR and MRI measurements can effectively predict the risk of ACL rupture. This helps expand the scope of the application of the LFCI and helps clinicians identify susceptible individuals who may benefit from targeted ACL rupture prevention counseling and intervention.