Anterior cruciate ligament remnant morphology is associated with preoperative rotational knee instability: A multicenter cohort study

Abstract Purpose To investigate the association between anterior cruciate ligament (ACL) remnant morphology, classified by Crain, and preoperative rotational knee instability after adjusting for preoperative and anatomical factors including time from injury to surgery and meniscal status. It was hypothesised that remnant morphology would be associated with rotational knee instability. Methods This retrospective multicenter cohort study was conducted between October 2022 and June 2025. Arthroscopic assessment categorised ACL remnants according to the Crain classification. Under anaesthesia, the Lachman and pivot‐shift tests were graded and dichotomised as high‐grade or low‐grade. Univariate comparisons were performed using the chi‐square test. Multivariate logistic regression identified predictors of high‐grade Lachman (L‐HG) and pivot‐shift (PS‐HG), adjusting for age, sex, body mass index, time from injury to surgery, mechanism of injury, Tegner Activity Scale (TAS) score, and medial and lateral meniscal tears, with Crain Type 4 as the reference. Results Among 304 patients, Crain types were as follows: Type 1 (16.8%), Type 2 (40.8%), Type 3 (27.6%) and Type 4 (14.8%). Overall, L‐HG and PS‐HG occurred in 36.8% and 39.8% of patients, respectively. L‐HG did not differ among the Crain groups ( p = 0.081), whereas PS‐HG did ( p = 0.016). In multivariate analysis, TAS score (odds ratio [OR] per unit, 0.83; 95% confidence interval [CI], 0.70–0.98; p = 0.028) and lateral meniscal tear (OR, 2.16; 95% CI, 1.31–3.58; p = 0.003) were significant predictors of L‐HG. For PS‐HG, Crain Type 3 had lower odds compared with Type 4 (OR, 0.43; 95% CI, 0.19–0.99; p = 0.048). Conclusions Crain remnant morphology was associated with rotational instability, with Type 3 demonstrating lower odds of high‐grade pivot shift than Type 4. These findings suggest that ACL remnant morphology may play a role in rotational instability. Level of Evidence Level IV, cohort study.