The supraspinatus is a relatively small yet important muscle located in the shoulder, playing a role in a wide array of arm movements. It is one of the four muscles that make up the rotator cuff, a group of muscles and their tendons that surround the shoulder joint. This muscle contributes to the shoulder’s extensive range of motion, allowing for various daily actions.
Where the Supraspinatus Sits
The supraspinatus muscle is found in the upper back, within a depression on the shoulder blade called the supraspinous fossa. From this origin, the muscle fibers converge into a tendon that extends laterally. This tendon then travels towards the upper arm bone, the humerus, where it inserts onto a bony prominence called the greater tubercle.
As the most superior of the four rotator cuff muscles, the supraspinatus sits above the infraspinatus, teres minor, and subscapularis. These muscles collectively stabilize the head of the humerus within the shoulder joint. The supraspinatus tendon follows a path beneath the acromion, which is a bony projection of the scapula. This creates a narrow passageway, significant for shoulder mechanics.
How the Supraspinatus Works
The supraspinatus muscle primarily initiates arm abduction (lifting the arm away from the body), particularly contributing to the first 0 to 15 degrees of elevation. Beyond this initial range, the larger deltoid muscle becomes the main contributor to continue lifting the arm.
The supraspinatus also contributes to the stability of the shoulder joint. It helps to hold the head of the humerus firmly pressed against the glenoid fossa, the shallow socket of the shoulder blade. The coordinated effort of the supraspinatus with the other rotator cuff muscles ensures smooth and controlled motion.
Common Supraspinatus Issues
The supraspinatus is a frequently affected part of the shoulder, often experiencing issues such as tendonitis, impingement syndrome, and tears. Tendonitis is inflammation of the supraspinatus tendon, often resulting from repetitive overhead motions (e.g., swimming, tennis, or painting). Symptoms include pain, stiffness, and weakness, particularly when lifting the arm sideways or at night.
Shoulder impingement syndrome often occurs when the supraspinatus tendon and the bursa, a fluid-filled sac that reduces friction, become compressed. This compression typically happens as they pass through the narrow space located beneath the acromion. Factors contributing to impingement can include swelling from tendonitis, the presence of bone spurs, or variations in the shape of the acromion itself. Symptoms of impingement are similar to tendonitis, frequently worsening with overhead arm movements and often presenting as pain through a specific arc of motion.
A tear in the supraspinatus refers to a rupture of its tendon, which can be either partial or extend completely through the tendon. These tears can occur from acute trauma, such as a fall onto an outstretched arm or from heavy lifting. Additionally, age-related degeneration and chronic wear and tear contribute significantly to the development of these tears. For instance, over half of individuals in their 80s may have some form of a supraspinatus tear, often affecting the dominant arm. Symptoms can include pain, weakness, and a restricted range of motion, appearing either suddenly after an injury or gradually over time with degeneration.