Development of Anatomic Risk Factors for ACL Injuries: A Comparison Between ACL-Injured Knees and Matched Controls

Background: Several tibiofemoral anatomic features have been repeatedly associated with increased anterior cruciate ligament (ACL) injury risk. Previous studies have highlighted age and sex differences among these anatomic risk factors, but little is known about the normal and pathologic development of these differences during skeletal maturation. Purpose: To investigate differences in anatomic risk factors at various stages of skeletal maturation between ACL-injured knees and matched controls. Study Design: Cross-sectional study; Level of evidence, 3. Methods: After institutional review board approval, magnetic resonance imaging scans from 213 unique ACL-injured knees (age, 7-18 years, 48% female) and 239 unique asymptomatic ACL-intact knees (age, 7-18 years, 50% female) were used to measure femoral notch width, posterior slope of the lateral and medial tibial plateau, medial and lateral tibial spinal height (MTSH, LTSH), medial tibial depth, and posterior lateral meniscus-bone angle. Linear regression was performed to assess change in quantified anatomic indices with age for male and female patients in the ACL-injured cohort. Two-way analysis of variance with Holm-Sidak post hoc testing was performed to compare anatomic indices between ACL-injured knees and ACL-intact controls in each age group. Results: In the ACL-injured cohort, notch width, notch width index and medial tibial depth increased with age (R-2 > 0.1; P < .001) in both sexes. MTSH and LTSH increased with age only in boys (R-2 >= 0.09; P <= .001), whereas meniscus-bone angle decreased with age only in girls (R-2 = 0.13; P < .001). There were no other age differences in quantified anatomic indices. Patients with ACL injury consistently had a significantly higher lateral tibial slope (P < .01) and smaller LTSH (P < .001) as compared with ACL-intact controls across all age groups and sexes. When compared with age- and sex-matched ACL-intact controls, ACL-injured knees had a smaller notch width (boys, 7-18 years; girls, 7-14 years; P < .05), larger medial tibial slope (boys and girls, 15-18 years; P < .01), smaller MTSH (boys, 7-14 years; girls, 11-14 years; P < .05), and larger meniscus-bone angle (girls, 7-10 years; P = .050). Conclusion: The consistent morphologic differences throughout skeletal growth and maturation suggest a developmental role in high-risk knee morphology. The observed high-risk knee morphology at an earlier age preliminarily suggests the potential of knee anatomy measurements in identifying those with a predisposition toward ACL injury.