This study aims to evaluate the clinical efficacy and biomechanical accuracy of a newly developed robot-assisted system for anterior cruciate ligament (ACL) reconstruction. ACL injuries are among the most common sports-related injuries in active individuals and athletes, and reconstruction surgery is considered the gold standard for treatment. However, failure rates remain substantial-up to 10.3% in the general population and as high as 40% among high-demand patients, such as young athletes. One of the key technical factors contributing to graft failure is improper placement of the femoral and tibial bone tunnels during surgery, which affects graft isometry, kinematics, and long-term function.

This prospective, randomized, controlled clinical trial will include 120 adult patients with confirmed ACL rupture. Subjects will be randomly assigned to two groups: an experimental group undergoing robot-assisted arthroscopic ACL reconstruction, and a control group receiving traditional arthroscopic ACL reconstruction. The investigational robot system is a custom-designed platform that integrates three primary modules: (1) preoperative planning, (2) intraoperative surgical assistance, and (3) biomechanical evaluation. The robot is designed to support precise tunnel positioning using CT/MRI fusion, dynamic motion tracking during surgery, and post-placement assessment of graft trajectory, potential impingement, and mechanical stability.

Preoperative planning includes 3D reconstruction from CT and MRI imaging to identify optimal anatomical positions for the femoral and tibial tunnels. During surgery, the robot allows the surgeon to perform the procedure in a semi-active "cooperative control" mode, combining robotic precision with the surgeon's decision-making and dexterity. Unlike existing robotic platforms, this system enables limited patient limb movement and real-time position tracking, making it uniquely suited for arthroscopic procedures.

The primary endpoint of the study is anterior tibial translation at 2 years postoperatively, measured using the KT-1000 arthrometer to compare surgical and contralateral knees. Secondary endpoints include subjective knee function scores (Lysholm, Kujala, and Tegner), CT and MRI evaluation of tunnel placement and graft integration, and physical examination results. Follow-up will occur preoperatively and at 2 years postoperatively via in-person visits.

Sample size was calculated based on differences in Lysholm scores from prior navigation-assisted studies. With an alpha level of 0.05, a power of 0.90, and a 20% expected loss to follow-up, 60 patients will be enrolled in each group. Data will be analyzed using SPSS v22.0. Parametric and non-parametric tests will be applied as appropriate, including ANOVA, Bonferroni post-hoc comparisons, and Cochran's Q for repeated categorical variables. A p-value <0.05 will be considered statistically significant.

This study is conducted by the Department of Sports Medicine at Beijing Jishuitan Hospital, a leading orthopedic and trauma care center in China, affiliated with Capital Medical University. The project is supported by the Capital Clinical Special Diagnosis and Treatment Technology Research and Translational Application Program and involves collaboration with Beijing Tiansing Bomed Medical Devices Co., Ltd., which is responsible for the robotic platform development and maintenance.

Ethical approval has been obtained from the Institutional Review Board of Beijing Jishuitan Hospital. All patients will provide written informed consent before enrollment. The study complies with the Declaration of Helsinki, Good Clinical Practice (GCP) guidelines, and local regulations.

Expected outcomes of this study include evidence of improved tunnel placement accuracy, enhanced functional recovery, and potentially reduced failure rates with robot-assisted ACL reconstruction. If successful, this research may contribute to broader adoption of robotic technology in arthroscopic sports medicine surgery and support future innovations in orthopedic surgical robotics.

Inclusion Criteria:

• Age over 16 years old; Primary anterior cruciate ligament (ACL) rupture confirmed by physical examination and MRI; Surgery scheduled within 3 months of injury; Patients eligible for autograft ACL reconstruction using 8S-ST/G technique; Normal range of motion in the contralateral knee; Willingness to participate and sign informed consent.

Exclusion Criteria:

• Previous surgery on either knee; Multi-ligament injuries or complex injuries requiring additional procedures; History of rheumatologic or systemic inflammatory joint diseases; Moderate to severe osteoarthritis (Kellgren-Lawrence grade ≥ 2); Poor general health or contraindications to surgery; Refusal to participate or inability to follow up.