Mechanical strength of the rotator cuff and cable interface: a complete histological and biomechanical study

Purpose: This study sought to evaluate the biomechanical properties of the interface between the rotator cuff and the semicircular humeral ligament or rotator cable (RCa) using histological and biomechanical techniques.

Methods: Out of 13 eligible cadaver specimens, 5 cadaver shoulders with an intact rotator cuff were included, 8 were excluded due to an injured rotator cuff. The histological study enables us to describe the capsule-tendon interface between the infraspinatus tendon (IST) or supraspinatus tendon (SST) and RCa, and to detect loose connective tissue layers to determine their precise location and measure their length along the interface. The biomechanical study sought to characterize and compare the mechanical strength of the IST-RCa versus SST-RCa interfaces.

Results: The average thickness of the RCa was 1.44 ± 0.20 mm. The histological study revealed a loose connective tissue layer at the IST-RCa interface, a finding not observed at the SST-RCa interface. The biomechanical study showed that the rigidity of the SST-RCa interface (72.10^-2 N/mm) was 4.5 times higher than for the IST-RCa interface (16.10^-2 N/mm) and the average maximum forces reached were 19.0 N and 10.6 N for the SST-RCa and IST- RCa interfaces, respectively.

Conclusion: The IST-RCa interface consists of a loose connective tissue layer contrary to the SST-RCa interface. In parallel, two different groups in terms of the mechanical response were identified: the IST-RCa interface group had less rigidity and ruptured more quickly than the SST-RCa interface, therefore emerging as the most vulnerable interface and explaining a potential extension of rotator cuff tears.