Return-to-sport readiness after surgical ACL reconstruction using a mixed reality system (MotumXR): protocol for a single-center prospective cohort study

Abstract Anterior cruciate ligament (ACL) injuries are a major concern in pivoting sports such as soccer, resulting in prolonged absences from training and competition. Surgical ACL reconstruction is the standard treatment, yet many athletes remain at increased risk of re-injury after returning to pivoting sports. Return-to-sport assessments aim to identify residual deficits that could contribute to this risk. However, conventional assessments often rely on internally focused, controlled tasks that may not reflect sport-specific demands. Recent advances in extended reality (XR) enable externally cued, ecologically valid scenarios to be incorporated into controlled laboratory testing. This study aims to validate a novel semi-immersive XR soccer application (MotumXR). The system uses players’ movements to control a virtual avatar performing soccer-specific tasks to assess return-to-sport readiness and re-injury risk after ACL injury. This is a prospective, single-center clinical registry conducted at the MOTUM-Human Performance Institute near Innsbruck. Participants comprise athletes with ACL reconstruction and uninjured controls. After a medical check-up and standardized warm-up, all participants complete biomechanical assessments, including isokinetic quadriceps and hamstring strength testing, and functional movement tasks (bilateral and unilateral countermovement jumps, bilateral and unilateral drop jumps, and planned cutting), followed by the MotumXR assessment battery (bilateral header, unilateral header, standing header with shot at goal, and cutting maneuver). Biomechanical data are collected using 3D motion capture and two force plates. Follow-up at 6, 12, 24, and 60 months after surgery includes validated questionnaires to determine re-injury occurrence and return-to-sport status, with data collection ongoing. Ethical approval has been granted by the Ethics Committee of the Medical University of Innsbruck (EK-Nr: 1379/2023). The registry and its associated analyses were prospectively registered in the German Clinical Trials Register (DRKS-ID: DRKS00034096). Findings will be disseminated through peer-reviewed publications and scientific conferences.