Summary

The purpose was to determine whether ATT on MRI is reduced after anatomic ACLR. Furthermore, we aim to identify specific factors associated with fixed ATT after surgery.

Abstract

Introduction

Anterior cruciate ligament (ACL) deficiency leads to a passive alteration of the tibiofemoral relationship in the sagittal plane, the tibia is subluxated anteriorly relative to the femur. Cadaveric and biomechanical studies have shown that 3.5 mm of anterior translation of the lateral compartment (ATLC) is highly specific of complete ACL tears and that a 6 mm threshold is needed to produce a positive pivot shift test.
The following factors have been found to be positively correlated with the amount of anterior tibial translation (ATT) after ACL injury: increased posterior tibial slope (PTS), concomitant injuries (such as of the meniscus, articular cartilage, or anterolateral ligament), chronic ACL tears, and re-ruptures.
Increased values of ATT have been associated with inferior knee stability and worse clinical outcomes. ATT is also a common finding in cases of multiple ACL failures, therefore ATT is thought to be a risk factor for ACL failure.
Non-anatomic ACL reconstruction (ACLR) has been proven to be ineffective in reducing the tibia, however there is still controversy as to whether anatomic ACLR restores the native tibiofemoral relationship. There are no studies comparing preoperative and postoperative MRI to determine whether ACLR reduces ATT.

Purpose

To determine whether ATT on MRI is reduced after anatomic ACLR. Furthermore, we aim to identify specific factors associated with fixed ATT after surgery.

Methods

We retrospectively analyzed all consecutive patients who underwent primary anatomic ACLR from January 2015 to December 2019 at our hospital. Patients who had preoperative and postoperative MRI at our institution were included. Anterior translation of the lateral and medial compartments (ATLC and ATMC) relative to the femoral condyles was measured on MRI. The difference between preoperative and postoperative ATLC was the primary outcome. According to ATLC on preoperative MRI the population was divided into groups: Group 1: <6mm, Group 2: 6 – 9.9mm, and Group 3: =10mm. We defined "fixed ATT" as cases with ATLC =6mm on postoperative MRI. Predictors of fixed ATT of the lateral compartment, including demographic variables, PTS, injury to the anterolateral ligament (ALL) and concomitant meniscal injuries, were assessed by multivariable conditional logistic regression analysis.

Results

A total of 221 patients were included. Although the mean difference in ATLC between preoperative and postoperative MRI was 0.69mm (p<0.01), 62% (n=137) of cases presented =6mm of ATLC on postoperative MRI (fixed ATT). After dividing the population into the three groups aforementioned, the only significant difference found was the amount of ATLC on postoperative MRI (p<0.001). Group 3 (=10mm) showed a higher number of delayed surgeries and increased PTS in comparison to the other groups. In cases of fixed ATT the only factor that presented a significant association was the degree of preoperative ATLC, no other factors studied were significant.

Conclusion

This is the first study with preoperative and follow-up MRI to analyze ATT after ACLR. Anatomic ACLR did not restore the tibiofemoral relationship, many patients (62%) remained with 6mm or more of ATLC postoperatively. The only factor associated with fixed ATT was the degree of preoperative ATLC.