Initiation and progression of rotator cuff tears due to fatigue loading: a cadaveric study

Rotator cuff (RC) tears are one of the most common tendinous injuries in the adult population, resulting in pain and loss of function. While many tears are often asymptomatic, many patients will experience tears progression and the development of symptoms. The objective of this study is to determine the location of RC tear initiation and the subsequent biomechanical changes as a function of tear size.

8 fresh-frozen (n = 8) human cadaveric supraspinatus tendons (mean age: 68.6 ± 14.2) were subjected to fatigue loading. Images were taken to capture the location of tear initiation and subsequent progression. Tendon stiffness and nominal strain were measured throughout the tendon's lifecycle to determine changes to the biomechanical properties as a function of tear size.

The location of tear initiation was 15.89 $\pm$ 3.33 mm (range: 13.00-22.22 mm) from the anterior edge of the supraspinatus tendon. As tears progressed, tendon stiffness decreased (R² = 0.68, P < .001) and nominal strain increased (R² = 0.71, P < .001). Biomechanical changes to the supraspinatus tendon occurred between the following tear sizes: 0-100 mm² and 100-200 mm² (P = .001) and between 100-200 mm² and 400 mm² or larger (P < .001).

In a biomechanical model of RC tears induced by fatigue loading, tear initiation was observed approximately 16 mm posterior to the biceps tendon, positioning it further posterior than previously believed. Alterations to the biomechanical properties occur due to tear progression. However, these changes are most severe and significant when tears progress to >100 mm² and further progress to >400 mm². These insights provide a potentially clinically relevant definition of tear progression based on biomechanical changes to the supraspinatus tendon.