An in vitro study of glenohumeral performance after suprascapular nerve entrapment

Purpose: The functional performance of athletes with suprascapular nerve entrapment remains unaddressed biomechanically. The purpose of this study was to investigate the glenohumeral joint kinematics, stability, and characteristics of joint contact. Methods: The investigation used an in vitro model simulating muscle palsy due to the suprascapular nerve entrapment. The experiment was performed in three clinically relevant positions: inferior, one by sulcus test; posterior, one with 90° flexion and maximal internal rotation; and anterior, one with 90° abduction and 90° external rotation (which is critically involved in several sports activities). Results: Simulated palsy due to suprascapular nerve entrapment had effects on glenohumeral joint stability and contact characteristics. Changes in the humeral head displacement and the glenohumeral joint contact characteristics were the most significant in the anterior direction when the arm in 90° abduction and 90° external rotation. Conclusion: Glenohumeral function is affected by muscle weakness at the position that is critical in sports activities. Because the infraspinatus supplies 90% of the external rotation power of the shoulder and the supraspinatus stabilizes the humeral head in the glenoid during elevation, residual weakness due to suprascapular nerve entrapment may preclude a safe return to athletics.