The Influence of Partial and Full Thickness Tears on Infraspinatus Tendon Strain Patterns

Abstract

Tears on the bursal and articular sides of the rotator cuff tendons are known to behave differently and strain is thought to play a role in this difference. This study investigates the effect of tear location on the changes in three strain measurements (griptogrip, insertion, and midsubstance tissue) in a sheep infraspinatus tendon model during axial loading. We introduced a 14 mm wide defect near the insertion from either the articular or bursal side of the tendon to three depths (3 mm, 7 mm & full) progressively. For each condition, tendons were sinusoidally stretched (4% at 0.5 Hz) while insertion and midsubstance strains were tracked with surface markers. For a fixed load, griptogrip strain increased significantly compared to intact for both cuts. Insertion strain increased significantly for the bursalside defect immediately but not for the articularside until the 66% cut. Midsubstance tissue strain showed no significant change for partial thickness articularside defects and a significant decrease for bursalside defects after the 66% cut. All full thickness cuts exhibited negligible midsubstance tissue strain change. Our results suggest that the tendon strain patterns are more sensitive to defects on the bursal side, and that partial thickness tears tend to induce localized strain concentrations in regions adjacent to the damaged tissue.