A tendon is a tough, fibrous connective tissue connecting muscles to bones. The supraspinatus tendon is a structure within the shoulder, contributing to its movements and stability. It is a component of the rotator cuff, a group of muscles and tendons surrounding the shoulder joint. Its integrity is important for proper shoulder function.
Its Location in the Shoulder
The supraspinatus tendon is positioned in the upper part of the shoulder, arising from a muscle that originates on the shoulder blade, also known as the scapula. Specifically, the supraspinatus muscle begins in the supraspinous fossa, a shallow depression located on the posterior surface of the scapula, above its spine. From this origin, the muscle fibers converge into the tendon, which then extends laterally. This tendon passes beneath the acromion, which is a bony projection forming the highest point of the shoulder.
The tendon continues its path over the head of the humerus, the upper arm bone, and inserts onto the superior facet of the greater tubercle of the humerus. This anatomical arrangement means the supraspinatus tendon effectively bridges the gap between the shoulder blade and the upper arm bone. It is the most superiorly located of the four rotator cuff muscles, which collectively form a cuff around the head of the humerus, helping to keep it centered within the shoulder socket.
How It Helps Your Arm Move
The supraspinatus muscle and its tendon contribute to shoulder movement and stability. Its primary function involves initiating the abduction of the arm, which is the motion of lifting the arm away from the body to the side. The supraspinatus is responsible for the first 0 to 15 degrees of this lifting motion before other muscles, like the deltoid, become more active.
Beyond initiating movement, the supraspinatus plays a role in stabilizing the head of the humerus within the glenohumeral joint, the main ball-and-socket joint of the shoulder. It helps compress the humeral head against the glenoid fossa, preventing it from riding up during arm elevation. This stabilization is important for efficient shoulder mechanics and allows for a wide range of motion. The supraspinatus works with the other rotator cuff muscles—the infraspinatus, subscapularis, and teres minor—to control and fine-tune shoulder movements.
Common Issues and What They Mean
The supraspinatus tendon is frequently affected by various conditions, largely due to its anatomical position and the stresses it endures during arm movements. One common issue is supraspinatus tendinitis, which refers to inflammation or irritation of the tendon. This condition often arises from repetitive stresses and overuse, particularly in activities involving overhead arm motions, such as certain sports or occupational tasks. The tendon can experience friction and compression as it passes under the acromion, which can contribute to its inflammation.
Another problem is a supraspinatus tendon tear, which can be either partial or full-thickness. A partial tear involves an incomplete disruption of the tendon fibers, while a full-thickness tear signifies a complete separation. These tears can result from acute traumatic events, such as a fall onto an outstretched arm or lifting a heavy object. They can also develop gradually due to age-related degeneration and chronic wear and tear, making the tendon weaker and more susceptible to injury. Factors like the shape of the acromion bone can influence the likelihood of these tears.