The supraspinatus muscle abducts and laterally rotates the shoulder, depresses, and stabilizes Post3the humeral head in the glenoid.  Because this muscle passes under the acromion, it is particularly vulnerable to injury when the shoulder is depressed.  If the humeral head glides superiorly, does not glide inferiorly during shoulder flexion and abduction, or does not rotate laterally enough to prevent impingement of the greater tuberosity against the coracoacromial ligament, then the supraspinatus muscle and tendon are exposed to compression forces. Continue reading