Mind the Notch: MRI Clues to Forecasting Unilateral and Bilateral ACL Injuries Using Notch Width Index

Abstract

A BSTRACT Anterior Cruciate Ligament (ACL) injuries are prevalent in the physically active population. Anatomical risk factors such as the Notch Width Index (NWI), the ratio of intercondylar notch width to bicondylar width, have been associated with ACL injury susceptibility. However, limited evidence exists on the predictive role of NWI in bilateral ACL injuries, which may reflect a distinct high-risk profile. A retrospective cross-sectional study was conducted on 141 individuals who underwent knee MRI. 70 had no ACL injuries (controls), while 71 had complete ACL tears. NWI was measured on MRI at the level of the popliteal groove. Two blinded radiologists calculated NWI. Multinomial logistic regression assessed the association between NWI and ACL injury type, using controls as reference. The mean age was 33.96 ± 12.12 years, with 83 males. Mean NWI was 0.259 ± 0.037. Lower NWI values were significantly associated with unilateral ( P = 0.001; OR = 1.342 × 10²²) and bilateral ACL injuries ( P = 0.001; OR = 3.384 × 10 32 ). The model showed good fit ( P = 0.985) with moderate explanatory power (Nagelkerke R ² =0.321). Stem-and-leaf plots demonstrated a progressive narrowing of NWI across groups. MRI-based NWI is a strong predictor of both unilateral and bilateral ACL injuries. Bilateral ACL injury cases may represent a distinct high-risk anatomical phenotype. NWI could serve as a valuable screening tool to identify at-risk individuals for targeted preventive interventions.