Strain of the Superior Labrum During Throwing Motion: A Cadaveric Study

Abstract

The purpose of this study was to determine the strain on the superior labrum, both anterior and posterior with the arm in simulated positions of the pitching motion. Ten fresh frozen cadaveric shoulders were used. After removal of the superficial soft tissues, the anterior and posterior cuff muscles were elevated from the scapula and loads applied to stabilize the humeral head. The supraspinatus muscle was elevated from its humeral insertion to visualize the biceps-labral complex. Using linear transducers, the strain in the anterior and posterior superior labrum was measured with the arm in various planes and rotations simulating the pitching motion: early cocking, late cocking, acceleration, deceleration and follow-through. Predetermined loads according to % maximum voluntary contraction (%MVC) of the biceps muscle during each phase of pitching were calculated and applied to the long head of the biceps tendon using a spring device. The increase in the strain was statistically significant for the anterior and posterior portions of the labrum during the late cocking phase than with all the other phases. The increased strain in the posterior portion of the superior labrum may be due to the anatomical orientation of the long head of the biceps at the superior labrum.