Intratendinous strain fields of the intact supraspinatus tendon: the effect of glenohumeral joint position and tendon region.

Rotator cuff tears are a common shoulder pathology and are hypothesized to relate to excessive tissue deformation. Few data exist, however, describing deformation of the rotator cuff as an intact, functional unit. Our purpose was to determine regional variations of intratendinous rotator cuff strain over a range of clinically relevant joint positions. A novel, MRI-based technique was utilized to quantify intratendinous strains in cadaveric shoulder specimens at 15 degrees, 30 degrees, 45 degrees, and 60 degrees of glenohumeral abduction in the scapular plane. The strain data were grouped into superior, middle, and inferior locations across the region where most rotator cuff tears occur clinically. A repeated measures ANOVA assessed the effects of joint position and tendon region on intratendinous strain. Few differences in intratendinous strain existed across tendon regions, but joint position had a pronounced effect. Specifically, intratendinous strain increased with increasing joint angle, and the 60 degrees strain was significantly greater than the 15 degrees strain across all tendon regions. These data suggest that joint position plays a larger role in rotator cuff mechanics than previously believed. Future studies will utilize this technique for quantifying intratendinous strain to assess the effects of partial-thickness rotator cuff tears.