The shoulder or glenohumeral (GH) joint is one of the most commonly dislocated and injured large joint. It is unstable as it has the greatest range of movement of any synovial joint in the body. The rotator cuff is composed of the four muscles which wrap around the GH joint like a collar.
Muscle Injury and Pain in the Glenohumeral Joint
Tears and sprains in the rotator cuff are common sports injuries, especially in individuals who have repetitive movements involving throwing or raising the arm such as in throwing and racquet sports. Injury and wear and tear of the muscles in the rotator cuff can lead to degenerative tendonitis and inflammation of the subacromial bursa.
The shoulder or glenohumeral (GH) joint has very little support inferiorly (or from its underside) and is particularly at risk of dislocation and injury in the abducted position (when the arm is raised). Nerve injury is also common in this area because the axillary nerve (which runs from the underarm) comes in close contact with the joint. This nerve damage can cause paralysis or numbness in the deltoid muscle (at the back of the shoulder), making it difficult to raise the arm up towards the head and a loss of sensation over the outer part of the arm.
The Muscles of the Rotator Cuff in the Shoulder Joint
Along with bone articulations and ligaments, the shoulder joint muscles help to stabilize the GH joint. The four rotator cuff muscles are the supraspinatus, infraspinatus, teres minor and subscapularis.
- The supraspinatus muscle supports the GH joint superiorly and works in raising the joint to extend the arm up towards the head. This muscle arises from the spine or edge of the scapula (the wing like bone at the back of the shoulder) and ends to the greater tubercle (or round outgrowth) of the humerus bone of the upper arm.
- The infraspinatus muscle strengthens the underside of the shoulder joint and acts to laterally rotate the humerus bone (turn the arm outwards). It arises from the scapula bone and attaches to the greater tubercle of the humerus.
- The teres minor muscle supports the GH joint superiorly and also laterally rotates the arm. This muscle arises from the posterior or back surface of the scapula bone and attaches to the greater tubercle of the humerus in the upper arm.
- The subscapularis muscle supports the shoulder anteriorly or from the front and medially rotates the humerus (or turns the arm inward). This muscle arises from the anterior or front surface of the scapula bone and extends to the lesser tubercle of the humerus.
These four muscles form the musculotendinous rotator cuff which stabilizes the entire joint (except for the inferior or underside) and protects it. They work together to hold the head of the humerus (the ‘ball’) into the glenoid cavity (the "socket") of the scapula bone, by contracting. The rotator cuff muscles relax to allow the shoulder joint to move.
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Reference:
Gray, Henry: Gray's Anatomy, Anatomy of the Human Body 40th Edition, London, UK. 2008
Noreen Kassem - Noreen Kassem is a hospital doctor based in London, UK. She has extensive experience in clinical research and an undergraduate honors ...
