Sex-Specific Function and Morphology of the Anterior Cruciate Ligament During Skeletal Growth in a Porcine Model

Abstract

Pediatric anterior cruciate ligament (ACL) injuries are on the rise, and females experience higher ACL injury risk than males during adolescence. Studies in skeletally immature patients indicate differences in ACL size and joint laxity between males and females after the onset of adolescence. However, functional data regarding the ACL and its anteromedial and posterolateral bundles in the pediatric population remain rare. Therefore, this study uses a porcine model to investigate the sex-specific morphology and function of the ACL and its bundles throughout skeletal growth. Hind limbs from male and female Yorkshire pigs aged early youth to late adolescence were imaged using magnetic resonance imaging to measure the size and orientation of the ACL and its bundles, then biomechanically tested under anterior-posterior drawer using a robotic testing system. Joint laxity decreased (p<0.001) while joint stiffness increased (p<0.001) throughout skeletal growth in both sexes. The ACL was the primary stabilizer against anterior tibial loading in all specimens, while the functional role of the anteromedial bundle increased with age (p<0.001), with an earlier shift in males. ACL and posterolateral bundle cross-sectional area and ACL and anteromedial bundle length were larger in males than females during adolescence (p<0.01 for all), while ACL and bundle sagittal angle remained similar between sexes. Additionally, in situ ACL stiffness correlated with cross-sectional area across skeletal growth (r2=0.75, p<0.001 in males and r2=0.64, p<0.001 in females), but not within age groups. This study has implications for age and sex-specific surgical intervention strategies and suggests the need for human studies.

Degenerative changes are associated with severity of anterior cruciate ligament injury within the skeletally immature joint

“…The median T2* relaxation time was calculated for each ACL bundle. Additionally, the volume of each segmented tissue was recorded, and the cross-sectional area (CSA) of the AM and PL bundles, the complete ACL, MCL, and LCL were calculated as previously described (17,18).…”

“…Specifically, a study in adult patients reported similar joint stability after isolated AM and PL bundle injuries (11), while a study in pediatric patients reported better outcomes for AM bundle injuries (16). Furthermore, in a skeletally immature pig model, the biomechanical function of the AM and PL bundles of the ACL depends on age and sex, such that the AM bundle plays a larger functional role in older versus younger subjects and males compared to females (17,18). Since evidence regarding treatment of bundle-specific partial injuries in children and adolescents is sparse, there is a need for further investigation of long-term outcomes and degenerative changes in skeletally immature subjects.…”