Summary

This study demonstrated a significantly greater posterior condylar height difference with medial condyles being larger than lateral condyles among pediatric patients who suffered ACL rupture compared to controls. We speculate that this difference in distal femoral anatomy leads to a relative increase in valgus alignment with knee flexion, which is the most common position of ACL injury.

Abstract

Objectives: While many factors associated with pediatric and adolescent ACL injury have been investigated, to the authors' knowledge, no study has analyzed posterior femoral condyle asymmetry. Therefore, this cohort study was designed to investigate for any differences in medial and lateral posterior condyle morphology and distal femoral version when analyzing ACL-injured patients versus a control cohort. The authors hypothesized that pediatric patients who suffered ACL rupture will have a relatively larger ratio of anterior to posterior size of the medial posterior femoral condyle compared to the lateral posterior femoral condyle than the controls leading to increase structural valgus in knee flexion.

Methods

A total of 150 pediatric and adolescent patients (age range: 6-18 years) with a pre-operative knee MRI who underwent ACL reconstruction between February 2016 and June 2020 at an urban tertiary care orthopedic hospital were considered for inclusion. Cases were matched on sex, laterality of injury, and age at imaging within 1.5 years to controls. Controls were patients with knee MRI that did not have any ligamentous, tendinous, or meniscal tears. Medial and lateral posterior condylar height was measured for each participant. Condylar difference was calculated as medial posterior condylar height minus lateral posterior condylar height. The distal femoral version was calculated as the angle between the femoral posterior cortical axis and the posterior condylar axis. Mann-Whitney U tests were used to compare continuous variables. Two-tailed significance was set as a p=0.05.

Results

A total of 72 participants of the 150 patients identified were included in this analysis: 36 ACL-injured patients and 36 control subjects. Median age was 13.5±3.3 years for all participants. Posterior medial condylar height was greater than lateral condylar height in both cohorts. Condylar difference was noted to be 1.8 mm greater in cases than controls. (p=0.04), while external distal femoral version was noted to be 2.0° greater in cases than controls (p=0.03).

Conclusion

This study demonstrated a significantly greater posterior condylar height difference with medial condyles being larger than lateral condyles among pediatric patients who suffered ACL rupture compared to a matched control group. We speculate that this difference is distal femoral anatomy in ACL patients leads to a relative increase in valgus alignment with knee flexion, which is the most common position of ACL injury.