Summary
The ACL structural appearance on 3D-MRI improves during the first 2-years after primary ACL injury and evidence for regained ACL continuity is associated with both less knee laxity and better patient-reported outcomes.
Abstract
Background
Recent studies have provided evidence supporting the potential for a ruptured ACL to naturally regain a normalised structural appearance on magnetic resonance imaging (MRI), and that regained continuity of the ACL was associated with functional outcomes. Advancements in MRI technology have enabled acquisition and processing of high-quality MRIs.
Objectives: i) Describe the structural changes of the ACL, including fiber continuity, evaluated by three-dimensional (3D) MRI at 5 timepoints within 24 months after ACL rupture, and ii) investigate the relationship between evidence of ACL continuity and patient-reported and clinically assessed outcomes.
Methods
We included 129 consecutive patients, aged 15-40 years, with acute ACL injury from the prospective NACOX cohort. Patients were treated according to usual clinical practice, and at 24 months, 60 (47%) had received ACL reconstruction (ACLR). Patients were excluded from further analysis after ACLR.
At baseline and follow-ups (3-, 6-, 12-, and 24-months post ACL-injury), MRI scans were acquired with a 3T scanner using an isotropic 3D proton-density fat-saturated sequence. The 3D-MRI data were reconstructed on oblique coronal parallel to ACL, sagittal, and axial planes for the image analysis. The newly developed ACL Continuity Thickness and Shape (ACTS) score, evaluating overall ACL structure (0-4), fiber continuity (0-3), ligament thickness (0-2), shape (0-1) and injury location, was used for MR images assessment.
At the same follow-up time-points after injury, patients answered questionnaires about perceived knee function, knee stability and activity participation and were tested clinically for knee stability and muscle strength.
Data are presented descriptively, and between-group inference tests were performed with Pearson’s chi-squared test or Fisher’s exact test and Mann-Whitney U-test as appropriate.
Results
The overall ACL structure and fiber continuity improved with at least one step in ACTS grade in 31% of the patients at 3 months follow-up, and in 78% of the patients at the 24-months follow-up. Improvement in overall ligament and fiber continuity was evident in 98% of the patients with a thickened ACL at 3 months and 70% of the patients with a thinned ACL at 3 months.
The location of most ACL injuries was mid-substance (60%) or proximal (23%) and approximately two thirds of them (65% respectively 60%) showed an improvement by at least one step from baseline to the last assessment in the combined score for overall ACL structure and fibers continuity on ACTS.
Patients with evidence of ligament continuity on MRI had lower side-to-side difference in knee laxity (KT-1000), at 12-months (2.6mm, 95%CI=0.95-4.25, p=0.001) and 24-months (4.6mm, 95%CI=2.17-7.09, p<0.001) and tended to have better patient-reported outcomes (e.g. IKDC-SKF mean difference 13.6, 95%CI=-3.44-30.6, p=0.057) and isokinetic muscle strength (LSI mean difference 7.1Nm, 95%CI=-1.45-15.6, p=0.051) compared to patients with overall ACL structure not seen in continuity.
Conclusion
The status of the ACL on MRI in non-reconstructed patients often naturally improved during the first 24 months after acute ACL-injury and evidence for regained ACL continuity was associated with both less knee laxity and better patient-reported outcomes. This could be an important factor to consider in the clinical decision-making having ACLR or not.