Meniscus Injuries Alter the Kinematics of Knees With Anterior Cruciate Ligament Deficiency

BACKGROUND: Most knee joint biomechanics studies have involved knees with an isolated anterior cruciate ligament (ACL) injury. However, a large portion of patients with injured ACLs have accompanied meniscus tearing. In this study, the in vivo alteration of knee biomechanics after tearing the ACL with or without combined medial or lateral meniscus tear was investigated during stair-ascending activity. HYPOTHESIS: The kinematic behavior of ACL-deficient knees changes with a combined medial or lateral meniscus tear. STUDY DESIGN: Controlled laboratory study. METHODS: Twenty-one patients with injured ACLs (contralateral side intact) were recruited before undergoing ACL reconstruction. Among these patients, 5 had isolated ACL injuries (group I), 8 had combined ACL and medial meniscus injuries (group II), and 8 had combined ACL and lateral meniscus injuries (group III). Bilateral magnetic resonance scans were obtained on each patient to construct 3-dimensional anatomic knee models. Both knees were then scanned during stair-climbing activity using a dual fluoroscopic imaging system. The knee kinematics during stair climbing were reproduced using a bone model image matching method. Anteroposterior and mediolateral translations and axial tibial rotation of the knee during stair ascent were then compared between the injured and intact contralateral knees of the patients. RESULTS: On average, injured knees in groups I and III showed more than 2 mm increased anterior tibial translation close to full knee extension. In group II, no statistically significant difference was observed between the injured and contralateral side in anteroposterior translation. Near full extension, in groups I and III, injured knees had less than 1 mm of increased medial tibial translation compared with the contralateral side, whereas in group II, a 1.0-mm increase in lateral tibial shift was observed in the injured knees. With regard to axial tibial rotation, group I showed an increased external tibial rotation (approximately 5°), group II had little variation, whereas group III had increased internal tibial rotation (approximately 3°). CONCLUSION: The results of this study demonstrate that a combined ACL/meniscus injury could alter the kinematics of ACL-injured knees in a different way compared with knees with isolated ACL tears, depending on the pattern of the meniscus tear. Considering the varying effect of meniscus injuries on knee joint kinematics, future studies might focus on specific treatment of patients with combined ACL and meniscus injuries to protect the joint from abnormal kinematics and subsequent postoperative cartilage degeneration.