Combined anterior and rotational knee laxity measurements improve the diagnosis of anterior cruciate ligament injuries.

PURPOSE: This study analysed whether associating the side-to-side difference in displacement and the slope of the load-displacement curve of anterior and rotational knee laxity measurements would improve the instrumental diagnosis of anterior cruciate ligament (ACL) ruptures and help to detect different types of ACL tears. METHODS: Anterior and rotational knee laxity was measured in 128 patients with an arthroscopically confirmed ACL injury and 104 healthy controls. Side-to-side differences were determined for three variables in anterior laxity: anterior displacement at 200 N (ATD200), primary compliance from 30 to 50 N (PCA) and secondary compliance from 100 to 200 N (SCA). Furthermore, four variables in rotational laxity were considered: internal and external rotation at 5 N m (IR5/ER5) and compliance from 2 to 5 N m (C IR/C ER). Receiver operating characteristic curves allowed to determine thresholds, specificities and sensitivities to detect ACL lesions, based on single variables considered and combinations thereof. RESULTS: Sensitivity and specificity reached, respectively, 75 and 95 % for ATD200 (threshold: 1.2 mm) and 38 and 95 % for IR5 (threshold: 3.2 degrees ). If either two out of the three variables were positive for anterior laxity or both IR5 and C IR were positive, 81 % of patients were identified without a false positive. All patients for whom ATD200 was >3.7 mm, PCA > 48 mum/N or SCA > 17.5 microm/N had ACL remnants that were either totally resorbed or healed on the posterior cruciate ligament. CONCLUSION: Combined instrumented anterior and rotational knee laxity measurements have excellent diagnostic value for ACL injury, provided that several measurements be considered concomitantly. LEVEL OF EVIDENCE: Diagnostic study, Level III.