The human shoulder joint offers an exceptional range of motion, enabling complex upper limb movements. This mobility, however, comes with a trade-off: the shoulder is also one of the body’s most susceptible joints to instability and injury. Its intricate design relies on a sophisticated interplay of bones, ligaments, and numerous muscles working in concert to provide both movement and support.
Where is the Teres Minor Located?
The teres minor is a narrow, elongated muscle situated on the posterior, or back, aspect of the shoulder. It is one of four muscles that collectively form the rotator cuff, a group essential for shoulder movement and stability. This muscle lies inferior to the infraspinatus muscle and superior to the teres major muscle. The deltoid muscle, a larger, more superficial shoulder muscle, covers the teres minor.
The teres minor originates from the lateral border and the adjacent posterior surface of the scapula, which is the shoulder blade. Its fibers extend obliquely upwards and laterally towards the humerus, the upper arm bone. The muscle then inserts onto the inferior facet of the greater tubercle of the humerus, a bony prominence on the upper part of the humerus. The upper fibers of its tendon also blend with the posterior part of the shoulder joint’s capsule.
What Does the Teres Minor Do?
Its primary function is the external, or lateral, rotation of the arm. This action involves rotating the arm away from the body’s midline, such as when turning a doorknob clockwise or preparing to throw a ball. The teres minor works in conjunction with the infraspinatus muscle to achieve this external rotation.
Beyond external rotation, the teres minor also assists in adduction of the arm, which is the movement of bringing the arm closer to the body. While its contribution to adduction is relatively small, it helps control the descent of the arm after reaching overhead.
The Teres Minor’s Role in Shoulder Stability
As a component of the rotator cuff, the teres minor helps maintain the stability of the glenohumeral joint, which is the ball-and-socket joint where the head of the humerus meets the glenoid cavity of the scapula. By compressing the humeral head into the shallow glenoid cavity, the rotator cuff, including the teres minor, helps prevent dislocation.
The teres minor contributes to the dynamic stability of the shoulder, meaning it helps stabilize the joint during movement. It works to keep the humeral head centered within the shoulder socket as the arm moves through various ranges of motion. This stabilizing action is particularly important during activities that involve lifting or throwing, ensuring smooth and controlled movement while minimizing the risk of injury. Its consistent function helps to prevent the humeral head from sliding upward during arm abduction.