Dynamic and Static Analysis of Rotator CUFF (Supraspinatus Tendon) with Tensile Test

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Objective : The bursal-side (B-S) and the joint-side (J-S) layers of the supraspinatus tendon may be torn in the different mechanism. In this study, we attempted to clarify the difference of the histological characteristic and the biomechanical property between both layers with reference to the etiology of the rotator cuff tear.Materials and Methods : 50 supraspinatus tendons were resected from bilateral shoulders of fresh cadavers (28-79 yrs.). Histological sections from 10 supraspinatus tendons were made in the coronal and four cross planes at the musculotendinous junction, proximal and distal points of the critical portion and the insertion. In the biomechanical study, 40 supraspinatus tendons were divided horizontally into the B-S and J-S layers of equal thickness. Quasistatic tensile test was performed foe each layer and the elongation rates in the musculotendinous, tendinous and insertional portions were measured.Results : The tendon fibers of the supraspinatus were thicker in the B-S layer than in the J-S layer. The fibers in the J-S layer tapered toward the insertion. In the tensile test, the destroying stress to the B-S layer was greater than that to the J-S layer while the elastic modulus was lower in the former. The tendinous portion had the largest elongation rate in the B-S layer, while the J-S layer elongated evenly. 'Gross rupture' occurred in the proximal portion of the tendon in the B-S layer and near the insertion in the J-S layer. 'Concealed rupture' occurred near the insertion and reflected the degenerative changes of the enthesis.