Morphologic Risk Factor for ACL Rupture in Children Younger than Age 12: An Mri-Based Comparison

BACKGROUND: There are findings in the adult and adolescent literature regarding anatomic variation that may lead to traumatic disruption of the anterior cruciate ligament (ACL). Previous studies have found an interaction between age and various morphologic risk factors but have been underpowered in assessing younger pediatric patients. HYPOTHESIS/PURPOSE: The purpose of this study was to evaluate morphologic features of the knee in younger children to determine if any of these factors may contribute to risk of ACL injury in this age group. METHODS: A retrospective review of knee MRIs was performed on pediatric patients evaluated at our facility for confirmed ACL rupture. Seven measures were performed and three ratios were calculated, which were compared to an age-matched control cohort previously used to establish and publish normative data of childhood knee MRIs. They were then grouped for statistical purposes by age: “child” aged 5 – 11 years, and “adolescents” aged 12 – 19 years. A generalized linear model was used to assess interaction between age and ACL status. RESULTS: A total of 49 children age <12 years with ACL rupture were identified during the data collection period that met criteria for review. While intercondylar width and notch height index (NHI) were significant in the ACL-torn cohort at large (p=0.015 and p=0.001 respectively), this difference was not present in children. Conversely, tibial plateau to anterior tibial spine (ATS) height was different in ACL-torn children but not in adolescents (p=0.003). Notch Width Index (NWI) was significantly smaller in ACL torn children and adolescents (p<0.0001). When comparing age groups, NWI was the only variable that had minimal to no difference in the normal group, but a significant difference between children and adolescents in the ACL-torn group. No difference was found in Critical Notch Stenosis. CONCLUSION: Children and adolescents demonstrate the effect of multiple morphologic parameters on ACL tear risk. While there is overlap, there are risk factors specific to each age group. Uniquely, increased TP to ATS height was a risk factor for ACL tear in children. Despite the effect of age and ACL tear on NWI, there was no difference for Critical Notch Stenosis, suggesting that the current definition of critical notch stenosis should be adjusted. Given the difference between NWI in children and adolescents with ACL tear, it may be more appropriate to have age-based cutoffs for critical notch stenosis.