# Complete ACL injuries are associated with higher static tibial subluxation than partial ACL injuries or intact ACLs measured on MRI

## TL;DR

This study shows that MRI can detect greater tibial subluxation in complete ACL injuries compared to partial or intact ACLs, helping guide surgical decisions.

## Contribution

The study introduces MRI-based static tibial subluxation as a method to distinguish between complete and partial ACL injuries.

## Key findings

- Complete ACL injuries showed significantly higher tibial subluxation in both medial and lateral compartments compared to partial ACL injuries.
- Partial ACL injuries had greater anterior tibial subluxation in the medial compartment compared to intact ACLs.
- MRI subluxation measurements showed good to excellent reliability between and within raters.

## Abstract

To investigate static tibial subluxation on magnetic resonance imaging (MRI) as a potential method to quantify rotatory knee instability and differentiate between complete anterior cruciate ligament (ACL) injuries, partial ACL injuries, and intact ACL.

Consecutive patients who underwent knee arthroscopy between 2016 and 2021 were retrospectively reviewed and divided into two groups according to arthroscopically verified ACL status: partial (p‐ACL‐I) or complete ACL injury (c‐ACL‐I). Patients with p‐ACL‐I required ACL‐augmentation. The control group with an intraoperatively confirmed intact ACL (i‐ACL) and a meniscus injury was 1:1 matched to p‐ACL‐I considering age, sex and body mass index (BMI). Static tibial subluxation in the medial (MC) and lateral compartment (LC) was measured on preoperative MRI. Intraclass correlation coefficients (ICC) were calculated for inter‐ and intrarater reliability. Pairwise t‐test and multivariate logistic regression were used to identify differences with significance set at p < 0.05.

The final analysis included 136 patients, 30 patients with p‐ACL‐I (8 female, 28 ± 10 years, BMI 27 ± 5 kg/m2), 24 patients with an i‐ACL (6 female, 34 ± 11 years, BMI 28 ± 5 kg/m2) and 82 patients with c‐ACL‐I (26 female, 27 ± 11 years, BMI 26 ± 5 kg/m2). The static tibial subluxation was found to be greater in c‐ACL‐I (MC: 2.5 mm, LC: 6.8 mm) compared with the p‐ACL‐I (MC: −0.6 mm, LC: 1.7 mm) both in the MC and LC (p < 0.001). The static anterior tibial subluxation was greater in p‐ACL‐I (−1.1 mm) compared with i‐ACL (−4.1 mm) in the MC (p = 0.01). However, no significant difference between p‐ACL‐I (1.6 mm) and i‐ACL (0.9 mm) was found in the LC (p = 0.90). Intra‐ and interrater reliability analysis showed good to excellent agreement (ICC = 0.75–0.90).

Residual fibres in p‐ACL‐I stabilized static anterior tibial translation. Preoperative static MRI subluxation measurement may help to differentiate between c‐ACL‐I and p‐ACL‐I who require surgical intervention, as an adjunct to the decisive dynamic examination of knee instability.

Level III.