Early degenerative changes are different between partial and complete anterior cruciate ligament injury and associate with joint instability in a skeletally immature porcine model.

Objective: Anterior cruciate ligament (ACL) injuries are a major problem in the pediatric and adolescent populations. Some of these injuries are only partial; yet, there is limited data to inform clinical treatment of such partial tears. It is unknown how injury partial injury impacts long-term degenerative changes in the joint relative to complete injury. In this study, we hypothesized that partial (anteromedial (AM) or posterolateral (PL) bundle) tears would result in small levels of instability and degeneration relative to complete ACL tears and that the degree of degeneration would associate with joint instability.

Design: Partial (isolated AM or PL bundle) or complete ACL injury was arthroscopically created in 3-month-old juvenile pigs. The contralateral limb served as a sham-operated control. Six months after injury, joint biomechanics was assessed along with cartilage and meniscus degeneration (via magnetic resonance imaging [MRI], gross imaging, and histology).

Results: Joint laxity increases were minimal after PL bundle injury (difference relative to controls (confidence interval): 0.5 (-1.2-2.2) mm), minor after AM bundle injury (3.7 (2.0-5.4) mm), and major after ACL injury (15.8 (13.7-17.8) mm). Cartilage MRI T1ρ relaxation times increased minimally after PL bundle injury (-0.9 (-5.1-3.3) ms for lateral tibia), moderately after AM bundle injury (6.6 (1.7-11.4) ms), and substantially after ACL injury (10.8 (2.1-19.5) ms). Changes in meniscus volume followed a similar rank order. Degeneration was associated with the extent of joint destabilization.

Conclusions: These findings suggest that cartilage and meniscus degeneration in the skeletally immature joint are associated with joint laxity after partial and complete ACL injuries.