Summary
Anteromedial reconstructions can effectively reduce the load on the ACL in case of medial instability
Abstract
Background
The aim of this study was to compare the load reducing effect within the anterior cruciate ligament (ACL) in anteromedial rotatory instability. The potential of different types of anteromedial reconstructions (AMR) was investigated.
Hypothesis
It was hypothesized that the resulting load within the ACL would be better controlled by all tested AMR in comparison to a standard single-bunde sMCL reconstruction.
Methods
A kinematic rig, equipped with a pulley system, was used to test 8 unpaired knees with imposed tibial displacing loads (5 Nm external/internal rotation, and combined 89 N anterior translation in external rotation (anteromedial drawer test, AMD, Slocum test). Testing was performed in the intact, sMCL/dMCL sectioned, and AMR states. Four different AMR were assessed: (1) Modified Lind reconstruction; (2) dMCL/sMCL combination; (3) flat sMCL/dMCL reconstruction; and (4) Single-bundle sMCL reconstruction (SB). The ACL was cut from its tibial attachment and fixed to a custom-made load cell through a tibial tunnel, to simulate an ACL reconstruction. The ACL was then tensioned to 80N at 10° of flexion and neutral rotation. ACL force in 0, 30, 60, and 90 degree of flexion was recorded in neutral rotation for later reference. Resulting loads of the ACL was analyzed by a repeated measures 2-Way-ANOVA with Bonferroni post-hoc testing.
Results
Sectioning the sMCL/dMCL significantly increased ACL load during anterior medial drawer across all flexion angles and during external rotation from 0° to 60° of flexion compared to the native state (e.g., 79.2 N vs. 116.0 N at 30°, p < .01). This increase in ACL load during AMD was then significantly reduced (p < .05) throughout the entire range of motion (0–90°) by all anteromedial reconstructions (at 30° flexion: flat MCL 71.0 N, Lind 67.5 N, sMCL+dMCL 56.6) except for the single-bundle reconstruction. In ER, AMR restored ACL forces to levels comparable to the native knee, with significant differences compared to the MCL-deficient state (p < .05) at 30° and 60° of flexion (except for SB). Internal rotation (IR) was not significantly affected (p > .05) by AMR, given that both the ACL and posterior oblique ligament remained functionally intact.
Conclusion
In this biomechanical in vitro study, comparison of three medial reconstruction techniques demonstrated that adding an AMR restored the native ACL load profile in knees with combined sMCL/dMCL deficiency. All medial reconstruction techniques, except the single-bundle technique, achieved effective load control.
Clinical Relevance:
AMR may further decrease the likelihood of ACL failure in ACL/MCL combined injuries, considering that MCL instability is a significant risk factor for recurrent ACL instability.