The supraspinatus muscle is a shoulder muscle that connects the shoulder blade, or scapula, to the bone of the upper arm, the humerus. This muscle is involved in the abduction of the arm, meaning the raising of the arm up and away from the body. It also acts with other muscles as part of a group of muscles and tendons known as the rotator cuff, to resist the force of gravity, and to stabilize the shoulder. For example, it helps maintain the position of the arm after an object has been thrown.
Structurally, the originating supraspinatus muscle tendon is attached to the top part of the scapula. There is a shallow hollow above the spine of the scapula, and this is where the origin of the muscle is. The tendon then passes through a bony extension of the scapula called the acromion process, which forms a partial tunnel at the top of the shoulder. After emerging from the acromion process at the top of the arm, the muscle is attached by its insertion tendon to a point at the top of the humerus.
The abduction of the arm at the shoulder joint is performed by the supraspinatus muscle working in conjunction with another muscle, the deltoid muscle. A relatively small muscle, the supraspinatus is believed to act as an assistor to the deltoid, stabilizing the joint and providing some power, while the majority of the power required for the abduction movement is supplied by the larger deltoid muscle. The supraspinatus is most active during the first 30 degrees of the abduction of the arm; the raising of the arm further than 30 degrees is mostly due to the action of the deltoid.
A supraspinatus muscle injury can result in pain and weakness when the arm is raised away from the body. Another symptom that may be experienced is pain when pressure is applied to the front of the inside of the upper arm. Symptoms of this nature may be caused by a supraspinatus muscle tear, or by inflammation of the tendon of the supraspinatus, or of the muscle itself. Such injuries may be caused by overuse of the muscles, especially by excessive force while the arm is raised above shoulder level, or by a fall that causes physical trauma to the shoulder. Treatment may include the use of anti-inflammatory drugs and specially designed supraspinatus muscle exercises to rehabilitate the muscle.