The bursal and articular sides of the supraspinatus tendon have a different compressive stiffness

Objective. To measure the compressive stiffness of the supraspinatus tendon and to determine whether regional difference exists in the bursal and articular side of the tendon. Design. Indentation testing was performed on both the bursal and articular sides of the supraspinatus tendon, focused on the ‘critical area’, where rotator cuff tears often occur. Background. When the supraspinatus tendon wraps around the humeral head or is under impingement condition, compressive force on the tendon surface is expected. Therefore, compressive stress has been recently considered to be one of the important factors associated with the cuff tear. The mechanical properties would be essential for analytic modeling of stress distribution. Methods. Indentation tests were performed at 15 locations on the bursal and articular surfaces of the supraspinatus tendon. A mathematical model with exponential relationship was used to describe the measured force–deformation relationship and to calculate the compressive stiffness of the supraspinatus tendon. Results. The over-all initial stiffness on the bursal and articular sides of the tendon was significantly different. On the bursal side, the anterior third had a significantly higher initial stiffness than the other thirds on average. On the articular side, initial stiffness at location 10 mm proximal to the greater tuberosity was significantly higher than the rest on average. Conclusion. The compressive stiffness of the supraspinatus tendon was found to be non-homogenous throughout the structure.