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

## TL;DR

This study finds that the shape of the remaining anterior cruciate ligament after injury is linked to knee instability before surgery, especially for rotational movement.

## Contribution

The study demonstrates a novel association between ACL remnant morphology and rotational knee instability after adjusting for multiple preoperative factors.

## Key findings

- Crain Type 3 ACL remnants were associated with lower odds of high-grade pivot shift compared to Type 4.
- Lateral meniscal tears and Tegner Activity Scale score were significant predictors of high-grade Lachman test results.
- Rotational instability was more strongly associated with ACL remnant morphology than with other preoperative factors.

## Abstract

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.

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.

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).

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 IV, cohort study.