The infraspinatus is one of the four muscles forming the rotator cuff, a group of muscles and their tendons that surround the shoulder joint. This muscle plays a significant role in enabling various shoulder movements and contributing to the overall stability of the shoulder.
Where to Find the Infraspinatus
The infraspinatus muscle is situated on the posterior (back) surface of the scapula (shoulder blade). It is a thick, triangular muscle that largely fills the infraspinous fossa, a concave area below the prominent ridge (spine) of the scapula. It originates from the medial two-thirds of this fossa.
The muscle fibers converge into a tendon. This tendon then crosses the posterior aspect of the shoulder joint. It inserts onto the middle facet of the greater tubercle of the humerus, the upper arm bone. The infraspinatus lies beneath the trapezius and parts of the deltoid and is positioned inferior to the supraspinatus and superior to the teres minor, two other rotator cuff muscles.
What the Infraspinatus Does
The primary action of the infraspinatus muscle is the external rotation of the arm (lateral rotation). This movement involves rotating the humerus (upper arm bone) outwards, away from the body. Everyday examples of this action include turning a doorknob, combing hair behind the head, or preparing to throw a ball.
Beyond external rotation, the infraspinatus is an important contributor to the stability of the glenohumeral joint, the main shoulder joint. It works in conjunction with the other rotator cuff muscles—the supraspinatus, subscapularis, and teres minor—to keep the head of the humerus securely centered within the shallow socket of the shoulder blade, known as the glenoid fossa. This stabilization is particularly important during movements that involve lifting the arm or activities requiring precise control of the shoulder.
Common Issues and Care
The infraspinatus can be susceptible to issues, often from repetitive arm movements or trauma. Common problems include tendinopathy, which is irritation or inflammation of the tendon, and muscle strains or tears. These injuries can range from partial damage to a complete separation of the tendon from the bone. Athletes involved in overhead sports like swimming, tennis, or baseball are particularly at risk due to the frequent stress placed on the shoulder.
Symptoms include pain in the back or top of the shoulder, which may worsen with arm movement, especially external rotation. Weakness in the arm, a reduced range of motion, and pain at night are also common indicators. Sometimes, a pinching sensation, known as impingement, can occur if the tendon is compressed within the shoulder joint space. Maintaining good posture, engaging in balanced exercise, and gently stretching the shoulder can help support muscle health. If pain persists or worsens, consulting a healthcare professional is advisable for proper diagnosis and guidance.