Determination Of The Mechanical Properties Of The Rotator Cuff Tendons

Purpose:

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

Method:

The tests were done on a newly designed and built test-bench that performed the tests at a consistent rupture speed. The tests were done on four fresh frozen cadaver shoulders. The capsular and tendinous layers of the rotator cuff were divided leaving them only attached on the humeral side. Separate tensile tests were done on these tendons, after they were divided into 10 mm wide strips before testing. The tendon thickness was also measured.

Results:

The maximum force tolerated by these tendons is comparable. The elongation however is not the same; the tendinous part of the tendon elongated more. The strength of the “rotatorhood” was then determined. This is a thin layer of tendon extending beyond the greater tuberosity, connecting the supra-spinatus to the sub-scapularis via the bicipital groove. The 10 mm of the “rotator hood” ruptured at an average force of 70 Newtons.

Conclusion:

1. 1.

   The two layers of the rotator cuff contribute equally to the cuff's strength.

2. 2.

   The difference in elongation of the tendinous and capsular layers makes the capsular layer more vulnerable to elongation stress.

3. 3.

   The “rotatorhood” is a strong important structure with a mechanically advantageous insertion.