This project aims to establish a high-quality, large-scale, single-center bidirectional cohort study to evaluate the postoperative clinical efficacy of ACLR combined with ALC augmentation in a specific high-risk population-patients with ACL rupture exhibiting excessive internal tibial rotation subluxation (EIRTS) on preoperative MRI. The study population will consist of patients with primary ACL rupture, and high-risk individuals will be identified based on the presence of EIRTS on preoperative knee MRI. The exposure group will undergo ACLR combined with ALC augmentation, while the control group will receive standard ACLR. Observational indicators will include all baseline patient characteristics and postoperative clinical outcomes.

Anterior cruciate ligament (ACL) rupture is one of the most common sports injuries in the field of sports medicine and significantly impairs athletic function. Autologous hamstring tendon single-bundle ACL reconstruction (ACLR) is the standard surgical technique for treating ACL rupture. Although most patients can return to sports postoperatively, a subset still experiences graft re-rupture, residual rotational instability of the knee, and other cases of reconstruction failure. Recent studies suggest that concomitant injury to the anterolateral complex (ALC) of the knee may be an important contributing factor. However, there is currently a lack of clinical evidence regarding the diagnosis of ALC injuries and the surgical indications for their treatment. Therefore, whether ALC should be augmented (diagnostic and surgical indications) in addition to routine ACLR, and how it should be augmented (surgical techniques), has become a key focus of current research.

This project aims to establish a high-quality, large-scale, single-center bidirectional cohort study to evaluate the postoperative clinical efficacy of ACLR combined with ALC augmentation in a specific high-risk population-patients with ACL rupture exhibiting excessive internal tibial rotation subluxation (EIRTS) on preoperative MRI. The study population will consist of patients with primary ACL rupture, and high-risk individuals will be identified based on the presence of EIRTS on preoperative knee MRI. The exposure group will undergo ACLR combined with ALC augmentation, while the control group will receive standard ACLR. Observational indicators will include all baseline patient characteristics and postoperative clinical outcomes.

The study includes two follow-up time points: 2 years and 5 years postoperatively. Follow-up will be conducted via outpatient visits and telephone interviews. Based on the follow-up outcomes, multivariate regression models will be used to analyze the association between exposure and clinical outcomes.

This cohort study aims to address treatment strategies for high-risk ACL rupture patients with preoperative EIRTS, thereby improving perioperative management and clinical decision-making in ACL injuries. It will provide important clinical evidence for establishing surgical indications for ALC augmentation and contribute to the development of long-term clinical prediction models for graft failure after ACLR. The findings will support innovation in ACL reconstruction techniques, optimization of perioperative strategies, reduction in postoperative graft failure rates, and improvement in return-to-sport rates. This study holds significant implications for advancing clinical research in the field of sports medicine.

Inclusion Criteria:

• Age ≥ 18 years; Primary unilateral ACL rupture; Preoperative knee MRI completed at our institution; Diagnosis of excessive internal tibial rotation subluxation (EIRTS) based on preoperative MRI measurements (i.e., internal rotation tibial subluxation [IRTS] > 5.8 mm); Patient has been informed of the study details and has provided written informed consent to participate in this cohort study.

Exclusion Criteria:

• Concomitant injury to the medial collateral ligament (MCL), lateral collateral ligament (LCL), or posterior cruciate ligament (PCL); History of contralateral knee injury; History of patellar dislocation; History of prior knee surgery.

Patients who underwent primary anterior cruciate ligament reconstruction at our institution and fulfilled the predefined inclusion and exclusion criteria.