The objective of this study was to determine the tensile strength of the different components of rotator cuff tendons.

A test bench that performs tests at consistent rupture speed was used to do separate tensile tests on 10-mm strips of capsular and tendinous layers in four fresh frozen cadaveric shoulders. The layers were left attached only on the humeral side.

The maximum force was comparable but the elongation of the outer part of the tendon was greater, indicating that the capsular part would tear first. On average, a 10-mm strip of capsular layer failed at 170N with elongation of 7 mm, while a 10-mm strip of tendinous layer failed at 230N with elongation of 10 mm.

Using six fresh frozen cadaveric shoulders, we went on to determine the strength of the rotator hood, a thin layer of tendon extending beyond the tuberosity major and connecting the supraspinatus to the subscapularis via the bicipital tunnel. The rotator hood ruptured at a mean force of 70 N.

We concluded that the two layers of the cuff contribute equally to the strength. It is therefore important to repair both layers. The difference in elongation of the tendinous and capsular layers makes the capsular layer more vulnerable to elongation stress. The rotator hood is a strong and important structure, and it is important to repair it.