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

Anterior cruciate ligament (ACL) injuries are a major problem in the pediatric and adolescent populations. Approximately one-quarter of these injuries extend through only part of the tissue cross-section. Yet, there is very limited data to inform clinical treatment for pediatric partial ACL tears. In particular, it is unknown how injury severity impacts long-term degenerative changes in the joint. In this study, we leverage a skeletally immature preclinical porcine model to evaluate joint biomechanics, tissue remodeling, and degeneration after partial (isolated anteromedial (AM) or posterolateral (PL) bundle) or complete (full thickness) ACL injury. Six months after injury, joint laxity increases were minimal for PL bundle injury, minor for AM bundle injury, and major for ACL injury. In both partial injury cases, the remaining bundle remodeled through an increase in cross-sectional area to attempt to restore ACL function and stabilize the knee joint. Joint degeneration (evaluated by cartilage T1 relaxation, macroscopic cartilage degeneration, and meniscal hypertrophy) was minimal after PL bundle injury, moderate after AM bundle injury, and substantial after ACL injury. The findings for partial injury were further substantiated in an older cohort of adolescent animals. Further analysis with subjects grouped by Lachman grade (indicating the extent of joint destabilization) indicated that degeneration was associated with the extent of biomechanical destabilization, irrespective of the injury type. These findings point to the importance of considering the results of joint laxity when creating treatment plans for young patients with significant growth remaining, particularly those with partial ACL injuries.