Structural Changes of the Anterior Cruciate Ligament (ACL), Evaluated by MRI, and Their Relation to Clinical Outcomes, Under Two Years After ACL Injury. Results From the Pragmatic NACOX-Cohort Study

OBJECTIVE: The aim was to i) describe structural changes of the anterior cruciate ligament (ACL) evaluated by MRI within 6 weeks until 24-months after ACL injury, and ii) investigate the relationship between ACL structural continuity and patient-reported and clinically-assessed outcomes. DESIGN: Longitudinal pragmatic cohort study METHODS: We included 129 patients, aged 15–40 years, with acute ACL injury from the NACOX cohort. Patients were treated according to common clinical practice which comprised supervised rehabilitation before considering ACL-reconstruction. At baseline and at 3, 6, 12, and 24 months follow-ups, 3-Tesla 3-dimensional proton-density fat-saturated MRIs, patient-reported and objectively-measured outcomes were assessed. The ACL Continuity, Thickness and Shape (ACTS) scoring system was used for MRI assessment. RESULTS: At 24 months, 60 (47%) participants had received ACL-reconstruction. At the last available MRI, 55 (48%) patients had overall ACL structure in continuity and 49 (43%) had ACL fibers in continuity. The overall ACL structure and fiber continuity on ACTS improved by at least one step in 31%–81% of the patients at the different follow-ups. Ligament structure in continuity was associated with fewer giving-way episodes (11% versus 50%, p = 0.033) and reduced knee laxity at 12-months (side-to-side difference ≥3mm: 53% versus 88%, p = 0.026) and 24-months (52% versus 100%, p = 0.013). Results on patient-reported outcomes were inconclusive due to wide confidence intervals. CONCLUSION: The ACL structure improved during the first 24 months after ACL injury when managed without ACL-reconstruction. Continuity of ligament structure was associated with less giving-way episodes and lower knee laxity.