The supraspinatus is a muscle forming part of what is known as the rotator cuff. This group of four muscles works together to provide stability and enable a wide range of motion in the shoulder joint. The supraspinatus is one of the more frequently discussed components of this system due to its specific contributions to arm movement and its susceptibility to certain conditions.
Anatomy and Location
The supraspinatus muscle is located on the posterior aspect of the shoulder blade, or scapula. It originates from the medial two-thirds of the supraspinous fossa, a shallow depression on the upper scapula. From this origin, the muscle fibers converge into a tendon.
This tendon then extends laterally, passing beneath the acromion, a bony projection of the scapula. The tendon travels over the head of the humerus, the upper arm bone, and blends with the shoulder joint capsule. It ultimately inserts onto the superior facet of the greater tubercle of the humerus. The supraspinatus is the most superiorly located of the four rotator cuff muscles.
Primary Functions
The supraspinatus muscle contributes to active movement and stability of the shoulder joint. Its primary function involves initiating shoulder abduction, lifting the arm away from the body. This muscle is particularly active during the initial 0 to 15 degrees of abduction, before the larger deltoid muscle takes over.
Beyond its role in initiating movement, the supraspinatus also stabilizes the humeral head within the glenoid cavity. It helps to resist gravitational forces that pull the arm downward and maintains the humeral head securely pressed against the glenoid cavity. This compressive force is important for dynamic glenohumeral stability.
Common Conditions Affecting the Supraspinatus
The supraspinatus muscle and its tendon are frequently affected by various conditions. Supraspinatus tendonitis, an inflammation of the supraspinatus tendon, commonly causes shoulder pain. This condition often results from overuse, repetitive overhead movements, or direct injury, and can lead to pain, stiffness, and weakness in the shoulder. Pain is often felt in the lateral, superior, or anterior shoulder, and may worsen with overhead activities or at night.
Impingement syndrome is another common issue, where the supraspinatus tendon becomes compressed as it passes through the subacromial space, the narrow passage beneath the acromion. This compression can lead to inflammation of the tendon and the bursa, a friction-reducing sac. Causes can include bony structures, such as bone spurs, or repetitive motions that narrow this space.
Tears of the supraspinatus tendon are also common, ranging from partial to full-thickness. A partial tear involves damage to only a portion of the tendon, while a full-thickness tear means the tendon is completely ruptured or detached from the bone. These tears can result from acute injuries, such as a fall or lifting a heavy object, or from gradual degeneration due to age and repetitive stress. Symptoms often include pain when lifting or lowering the arm, weakness, and difficulty sleeping on the affected side.