• Full Name: KUNANON AOWATSUWAN
• Affiliation/Institution: Department of Mechanical Engineering, Faculty of Engineering, Kasetsart University, 50 Ngam Wong Wan
• Country: Thailand

• Full Name: JARUTA THONGCHIM
• Affiliation/Institution: Department of Mechanical Engineering, Faculty of Engineering, Kasetsart University, 50 Ngam Wong Wan
• Country: Thailand

• Full Name: PINKAWAS KONGMALAI
• Affiliation/Institution: Department of Orthopedics, Faculty of Medicine, Kasetsart University, 50 Ngam Wong Wan Road, Lat Yao
• Country: Thailand

• Full Name: ATTAPORN WISESSINT
• Affiliation/Institution: Department of Mechanical Engineering, Faculty of Engineering, Kasetsart University, 50 Ngam Wong Wan
• Country: Thailand

Rotator cuff tears are among the most common shoulder injuries and can result in severe pain and restricted mobility. In full-thickness tears, complete tendon detachment may lead to significant functional loss. Surgical repair is often required when conservative treatments fail. Postoperatively, the arm is typically immobilized at approximately 30° of abduction; however, limited biomechanical evidence supports this standard positioning.

Objectives
This study aims to determine the optimal postoperative arm abduction angle that minimizes mechanical stress on repaired rotator cuff tendons, particularly the supraspinatus.

Study Design
A computational biomechanical analysis was conducted using the Finite Element Method. Stress distribution in the repaired tendon was evaluated at arm abduction angles of 5°, 15°, 30°, 45°, and 60°. Von Mises stress was used as the primary outcome measure.

Results
For the supraspinatus tendon, the lowest von Mises stress was observed at 15° (0.96 MPa). Higher stress values were found at 5° (9.38 MPa), 30° (7.82 MPa), 45° (1.80 MPa), and 60° (29.78 MPa). The results demonstrate clear differences in stress distribution across arm angles, with substantially increased stress at higher abduction angles, particularly 60°.

Conclusions
An arm position of 15° appears to be the most suitable angle for minimizing mechanical stress on the repaired supraspinatus tendon. Optimizing postoperative arm positioning may reduce mechanical overload and support improved tendon healing outcomes following rotator cuff repair.