Rotator cuff

  • The rotator cuff is a group of muscles in the shoulder region and their tendons that stabilize and strengthen the shoulder and allow its many movements. Four muscles form the rotator cuff, all of whom connect the scapula with the humerus.

    The four rotator cuff muscles are:

    The functions of the rotator cuff are connected with the glenohumeral joint, as it provides stability and motion in this joint.

    Disorders affecting the rotator cuff interfere with the function of the glenohumeral joint, causing the inability to perform movements in this joint, and is often accompanied by pain. The most common injury is a rotator cuff tear.

    Structure

    The rotator cuff is a musculotendinous structure. All four rotator cuff muscles originate from the body of the scapula, and their tendons insert on the tuberosities of the proximal humerus. The rotator cuff muscles transition into tendons as they near their attachment sites. The four tendons fuse to form the rotator cuff tendon. Along with the articular capsule of the glenohumeral joint, the coracohumeral ligament, and the glenohumeral ligaments, the four muscle tendons blend into a confluent sheet before inserting into the humeral tuberosities.

    All these soft-tissue structures, as well as the fibrous joint capsule, are important for stabilizing the glenohumeral joint.

    Function

    The rotator cuff provides several movements in the glenohumeral joint. However, even more importantly, this musculotendinous structure is essential in stabilizing the humeral head and the glenoid cavity.

    The glenohumeral joint lacks bony stability, so it relies heavily on both static and dynamic soft tissue stabilizers. The rotator cuff muscles help to maintain a stable core at the glenohumeral joint around which the other muscles of the shoulder girdle can effectively act on the humerus.

    In addition to stabilizing the glenohumeral joint, the rotator cuff muscles also provide several movements in this joint, including abduction, internal rotation, external rotation, and extension of the upper arm. Generally, each muscle of the rotator cuff provides a different set of motions.

    Rotator cuff muscles

    Supraspinatus

    The supraspinatus muscle (or simply supraspinatus, Latin: musculus supraspinatus) is a triangular muscle that fills the supraspinous fossa of the scapula. It originates from the supraspinous fossa, which is located on the posterior surface of the scapula and inserts on the greater tuberosity of the proximal humerus. The tendon of the supraspinatus muscle passes under the acromion, over the glenohumeral joint, and inserts on the superior facet of the greater tuberosity.

    The main functions of this rotator cuff muscle are to abduct the arm and to stabilize the shoulder joint. The innervation of the supraspinatus is provided by the suprascapular nerve (C5).

    Infraspinatus

    The infraspinatus (Latin: musculus infraspinatus) is also innervated by the suprascapular nerve (C5 - C6). The muscle originates from the posterior surface of the scapula, more precisely from the infraspinous fossa and inserts into the greater tuberosity of the humerus. The tendon of this muscle inserts on the middle facet of the great tuberosity. 

    The infraspinatus stabilizes the shoulder joint and provides external rotation of the upper arm.

    Teres minor

    The teres minor (Latin: musculus teres minor) is a round muscle that originates from the lateral border of the scapula below the infraglenoid tuberosity. It inserts into the inferior facet of the greater tuberosity of the humerus. It is innervated by the axillary nerve (C5).

    Like other rotator cuff muscles, it stabilizes the shoulder. It also provides external rotation and extension of the upper arm.

    Subscapularis

    The subscapularis (Latin: musculus subscapularis) is a large triangular muscle that fills the subscapular fossa of the scapula. It originates anteriorly along the lateral surface of the scapula and inserts on the lesser tuberosity of the proximal humerus. The subscapularis has a dual innervation by both the upper and lower subscapular nerves (C5 - C6), with the upper subscapular nerve innervating a larger portion of the muscle.

    The subscapularis is the larger and most powerful of the rotator cuff muscles. It provides internal rotation and adduction of the upper arm, while also stabilizing the shoulder joint.

    Innervation and blood supply

    Two of the rotator cuff muscles, the supraspinatus, and infraspinatus, are innervated by the suprascapular nerve. The axillary nerve innervates the teres minor. The subscapularis is innervated by both the upper and lower subscapular nerves. 

    The arterial blood supply to the rotator cuff muscles is generally provided by six branches of the axillary artery, with the most significant contributions arising from the suprascapular and the anterior and posterior circumflex humeral arteries.

    Common injuries

    Rotator cuff disorders are a leading cause of shoulder pain and shoulder-related disability. Most often, these disorders are associated with age-related degenerative changes but may also occur with an acute injury. The most common injury affecting this group of muscles is a rotator cuff tear. Among other common disorders are rotator cuff tendinitis and tendinopathy.

    The rotator cuff tear is an injury of one or more of the tendons of the rotator cuff. The most common tendon affected is that of the supraspinatus muscle. The symptoms of a rotator cuff tear may include pain, which usually increases with movement or weakness of the involved muscle, or shoulder stiffness. The most important causes of the damage are degenerative changes, repetitive microtraumas, and severe acute traumatic injuries. There are also many other possible causes, such as atraumatic injuries, intrinsic factors (for example, hypovascularity), as well as extrinsic factors, such as subacromial and internal impingement. A comprehensive history, structured physical examination, and radiographs are often sufficient to diagnose rotator cuff injuries, but additional imaging (for example, MRI) may be required to clarify the damage. The treatment for a rotator cuff tear may include rest, cold applications to the sore area, physical therapy, and surgery, as well as medications that reduce pain and swelling. Note, that not all cases of a rotator cuff tear require surgery.

    Another common injury is rotator cuff tendinitis, which is an acute inflammation of the rotator cuff soft tissue.

    Rotator cuff tendinopathy, on the other hand, is a chronic inflammation or degenerative process of the rotator cuff soft tissue.