Biomechanical Function of Anterior Cruciate Ligament Remnants: How Long Do They Contribute to Knee Stability After Injury in Patients With Complete Tears?

PurposeThis study aimed to evaluate the biomechanical function of anterior cruciate ligament (ACL) remnants in anteroposterior and rotational knee stability in patients with a complete ACL injury.MethodsACL remnants were classified into 5 morphologic patterns: group 1, bridging between the posterior cruciate ligament and tibia; group 2, bridging between the intercondylar notch and tibia; group 3, partial rupture of the posterolateral bundle; group 4, partial rupture of the anteromedial bundle; and group 5, no substantial ACL remnants. The decision of whether the remaining bundle represented partial or complete rupture of the ACL was made based on physical, magnetic resonance imaging, and arthroscopic findings in a comprehensive manner. Patients in groups 1 (n = 18) and 2 (n = 12) underwent intraoperative arthrometry with a navigation system before and immediately after resection of the ACL remnant. The effects of chronicity (duration between injury and surgery) and ACL remnant pattern on changes in knee laxity after debridement of the ACL remnant were investigated.ResultsChronicity had a significant effect on changes in anteroposterior knee laxity evaluated at 30° of knee flexion after resection of the ACL remnant (change in laxity of 2.22 mm for chronicity ≤1 year and 0.17 mm for chronicity >1 year). Chronicity did not influence changes in rotational knee stability after resection of the remnant. There were no significant differences between groups 1 and 2 with regard to any of the evaluated changes in knee stability.ConclusionsIn groups 1 and 2 ACL remnants contributed to anteroposterior knee stability evaluated at 30° of knee flexion for up to 1 year after injury, beyond which this biomechanical function was lost. Chronicity and remnant pattern did not influence changes in rotational knee stability after resection of the remnant.Level of EvidenceLevel III, diagnostic study of nonconsecutive patients.