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 arti cular 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 ro tator 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-deformatio n relationship and to calculate the compressive stiffness of the supraspina tus tendon. Results. The over-ah initial stiffness on the bursal and articular sides of the tendon was significantly different. On the bursal side, the anterior t hird had a significantly higher initial stiffness than the other thirds on average. On the articular side, initial stiffness at location 10 mm proxima l to the greater tuberosity was significantly higher than the rest on avera ge. Conclusion. The compressive stiffness of the supraspinatus tendon was found to be non-homogenous throughout the structure.