Noninjured Knees of Patients with Noncontact ACL Injuries Display Higher Average Anterior and Internal Rotational Knee Laxity Compared with Healthy Knees of a Noninjured Population

Background: Excessive physiological anterior and rotational knee laxity is thought to be a risk factor for noncontact anterior cruciate ligament (ACL) injuries and inferior reconstruction outcomes, but no thresholds have been established to identify patients with increased laxity. Purpose: (1) To determine if the healthy contralateral knees of ACL-injured patients have greater anterior and rotational knee laxity, leading to different laxity profiles (combination of laxities), compared with healthy control knees and (2) to set a threshold to help discriminate anterior and rotational knee laxity between these groups. Study Design: Case-sectional study; Level of evidence, 3. Methods: A total of 171 healthy contralateral knees of noncontact ACL-injured patients (ACL-H group) and 104 healthy knees of control participants (CTL group) were tested for anterior and rotational laxity. Laxity scores (measurements corrected for sex and body mass) were used to classify knees as hypolax (score <-1), normolax (between '1 and 1), or hyperlax (>1). Proportions of patients in each group were compared using ² tests. Receiver operating characteristic curves were computed to discriminate laxity between the groups. Odds ratios were calculated to determine the probability of being in the ACL-H group. Results: The ACL-H group displayed greater laxity scores for anterior displacement and internal rotation in their uninjured knee compared with the CTL group (P <.05). Laxity profiles were different between the groups for the following associations: normolax in anterior displacement/hypolax in internal rotation (6% [ACL-H] vs 15% [CTL]; P =.02) and hyperlax in anterior displacement/normolax in internal rotation (27% [ACL-H] vs 10% [CTL]; P <.01). The laxity score thresholds were 0.75 for anterior laxity and '0.55 for internal rotation. With both scores above these thresholds, a patient was 3.18-fold more likely to be in the ACL-H group (95% CI, 1.74-5.83). Conclusion: The healthy contralateral knees of patients with noncontact ACL injuries display different laxity values both for internal rotation and anterior displacement compared with healthy control knees. The identification of knee laxity profiles may be of relevance for primary and secondary prevention programs of noncontact ACL injuries.