The effect of supraspinatus tears on glenohumeral translations in passive pitching motion.

Abstract

Supraspinatus tears are common in pitchers. However, the effect of these tears on glenohumeral (GH) mechanics is incompletely understood. To describe the effect of supraspinatus tears and repairs on GH kinematics during an abbreviated throwing motion using the intact shoulder girdle. The hypothesis was that supraspinatus tears would lead to an increase of GH translation in the coronal plane and supraspinatus repairs would restore GH kinematics. Controlled laboratory study. Six shoulders from 3 fresh-frozen cadavers were tested in a novel 7 degrees of freedom robotic testing system. Torsos were mounted and the wrist was pinned to an actuator mounted on an upper frame. After the deltoid was removed, the shoulders were studied during an abbreviated throwing motion (ATM) from maximum external rotation to the midcoronal plane to establish a baseline. The ATM was repeated after creation of a 1-cm supraspinatus tear, after creation of a 3-cm supraspinatus tear, and after repair with a transosseous equivalent (TOE) technique. Retroreflective bone markers and high-speed infrared cameras were used to measure GH kinematics and calculate the center of rotation of the GH joint (CORGH) instantaneously. The 1- and 3-cm supraspinatus tears did not significantly alter GH translation. The TOE repair shifted the CORGH posteriorly, as evidenced by a significant decrease in the overall GH translation in all 3 planes (P = .003, .019, and .026, for x-y, y-z, and x-z planes, respectively). In contrast to a TOE repair of the supraspinatus tendon, isolated supraspinatus tears did not perturb GH kinematics in this cadaveric model of the throwing shoulder. In throwing athletes, treatment of rotator cuff tears should be addressed with caution to avoid an unintended alteration in GH kinematics due to overtightening of the tendon.