Context: Pediatric anterior cruciate ligament (ACL) injury rates are increasing and are highest in adolescent females. Complete ACL tears are typically surgically reconstructed, but there are few guidelines and very limited data regarding the need for surgical reconstruction or rehabilitation for partial ACL tears in skeletally immature patients.

Objective: To evaluate the impact of partial (anteromedial bundle) and complete ACL transection on joint laxity and tissue forces under anterior and rotational loads in male and female stifle joints throughout skeletal growth in the porcine model.

Design: Descriptive Laboratory Study.

Setting: Laboratory.

Patients or Other Participants: Sixty male and female Yorkshire cross-breed pigs aged 1.5, 3, 4.5, 6, and 18 months (n=6/age/sex).

Main Outcome Measure(s): Joint laxity was measured in intact, anteromedial bundle-transected, and ACL-transected joints under applied anterior-posterior drawer and varus-valgus torque using a robotic testing system. The loading of the soft tissues in the stifle joint was measured under each condition.

Results: Anterior-posterior joint laxity increased by 13–50% (p<0.05) after anteromedial bundle transection and 75–178% (p<0.05) after ACL transection. Destabilizations after anteromedial bundle transection increased with age (p<0.05) and were greater in late adolescent females than late adolescent males (p<0.05). In anteromedial bundle-transected joints, the posterolateral bundle resisted the anterior load. In ACL-transected joints, the medial collateral ligament (MCL) contribution was largest, followed by the medial meniscus. MCL contribution was larger while medial meniscus contribution was smaller in males versus females.

Conclusions: Partial ACL transection resulted in moderate increases in joint laxity, while the remaining bundle performed the primary ACL function. Destabilizations due to partial ACL transection were largest in late adolescent joints, indicating that operative treatment should be considered in active, late adolescent patients. Increased forces in the MCL and medial meniscus after ACL transection suggest that rehabilitation protocols may need to focus on protecting these tissues.

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