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The rotator cuff is a group of four muscles and tendons that attach to the shoulder bones and provide stability to the shoulder joint. These muscles include the supraspinatus, infraspinatus, teres minor, and subscapularis. The rotator cuff is responsible for a wide range of movements, including abduction, internal rotation, and external rotation of the arm. It also helps to stabilize the glenohumeral joint by compressing the humeral head against the glenoid cavity. Injuries to the rotator cuff are common, especially among athletes, and can cause shoulder pain and restricted movement.
| Characteristics | Values |
|---|---|
| Number of muscles | 4 |
| Muscle names | Supraspinatus, Infraspinatus, Teres Minor, Subscapularis |
| Function | Stabilise and centre the humeral head in the glenoid fossa, allowing a wide range of movement |
| Innervation | Suprascapular nerve, Axillary nerve, Lower subscapular nerve |
| Blood supply | Suprascapular artery, Subscapular artery, Posterior circumflex humeral artery |
| Attachments | Originates from the supraspinous fossa of the scapula, attaches to the humeral head |
| Common injuries | Rotator cuff syndrome, Impingement syndrome, Rotator cuff tears, Shoulder sprains, Swimmer's shoulder |
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What You'll Learn
Supraspinatus muscle
The supraspinatus muscle is one of the four muscles that make up the rotator cuff, along with the infraspinatus, teres minor, and subscapularis muscles. It is the smallest and most superiorly located of the four. The supraspinatus muscle is located deep to the trapezius muscle in the posterior scapular region, extending from the supraspinous fossa of the scapula to the proximal humerus. It originates from the medial aspect of the supraspinous fossa, a concave depression located above the spine of the scapula.
The supraspinatus muscle plays a crucial role in the stabilization of the glenohumeral joint, particularly during movements of the upper limb. It helps to keep the head of the humerus firmly pressed medially against the glenoid fossa of the scapula, resisting gravitational forces that act on the shoulder joint and preventing the sliding of the head of the humerus. This stabilization allows for a full range of motion and provides stability to the shoulder joint.
In addition to its stabilizing role, the supraspinatus muscle assists in the abduction of the arm. It is involved in both the initiation and continuation of abduction throughout the range of motion, working alongside the deltoid muscle. The supraspinatus muscle also contributes weakly to the lateral rotation of the humerus.
The supraspinatus muscle is susceptible to injuries, particularly tears, due to its frequent use in various activities. It is the most frequently torn muscle in the rotator cuff. Evaluating the integrity of the supraspinatus muscle can be done through special tests such as Jobe's test, commonly known as the ""empty can" test, which assesses the muscle at 90 degrees of abduction and internal rotation.
The supraspinatus muscle receives its vascular supply primarily from the suprascapular artery, a branch of the thyrocervical trunk of the subclavian artery. It is also innervated by the suprascapular nerve, formed by the anterior rami of spinal nerves C5 and C6.
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Infraspinatus muscle
The infraspinatus muscle is one of the four muscles that make up the rotator cuff, a functional anatomical unit located in the upper extremity. The rotator cuff muscles all originate from the scapula (shoulder blade) and insert into the humerus (upper arm bone). The main function of the rotator cuff is to stabilise and centre the humeral head in the joint socket, the glenoid cavity. The infraspinatus muscle is a thick, triangular muscle that occupies the chief part of the infraspinatous fossa. It attaches medially to the infraspinous fossa of the scapula and laterally to the middle facet of the greater tubercle of the humerus. The infraspinatus muscle is innervated by the suprascapular nerve, which originates at the superior trunk of the brachial plexus. This nerve also innervates the supraspinatus muscle, which is another muscle of the rotator cuff.
The infraspinatus muscle plays a crucial role in the external rotation of the humerus and stabilisation of the shoulder joint. When the arm is fixed, the infraspinatus abducts the inferior angle of the scapula. This movement, known as scaption, increases the mobility of the scapula, assisting other shoulder muscles in achieving full shoulder abduction. The infraspinatus also works synergistically with the teres minor muscle to rotate the head of the humerus outward and assist in carrying the arm backward.
The infraspinatus muscle is particularly susceptible to rotator cuff tears due to its large insertion area on the humerus. Rotator cuff tears can cause sudden and intense shoulder pain and arm weakness. Evaluation of the infraspinatus muscle can be performed through lateral rotation against resistance with the elbow flexed and the arm in a neutral abduction/adduction position.
The infraspinatus muscle has evolutionary roots in the pectoral muscles of early mammals. Over time, some fibres of the pectoral muscle sheet attached to the scapula and evolved into the supraspinatus, infraspinatus, and parts of the subscapularis.
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Teres minor muscle
The teres minor muscle is one of the four muscles of the rotator cuff. It is a narrow, elongated posterior muscle of the shoulder that extends between the scapula and the head of the humerus. The muscle originates from the lateral border and adjacent posterior surface of the corresponding right or left scapula. The attachment site spans the upper two-thirds of the lateral border of the scapula. The fibres quickly fuse into a single muscle belly, which courses superolaterally towards the proximal humerus. Teres minor inserts onto the greater tubercle of the humerus.
The primary function of the teres minor is to modulate the action of the deltoid, preventing the humeral head from sliding upward as the arm is abducted. It also functions to rotate the humerus laterally, providing stability to the shoulder joint. The muscle is innervated by the axillary nerve, which stems from the posterior cord of the brachial plexus.
The teres minor can be evaluated for injuries using the hornblower's test. The patient's arm should be at 90 degrees in the scapular plane, with the elbow flexed. The patient will then externally rotate against resistance, attempting to form a "field goal" sign. The test is positive if the patient is unable to rotate their shoulder externally, indicating minor pathology.
Atrophy of the teres minor muscle is often a consequence of a rotator cuff tear. Selective atrophy of the teres minor muscle has been linked to compression of the corresponding axillary nerve branch or posterior humeral circumflex artery.
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Subscapularis muscle
The subscapularis muscle is a large, triangular-shaped muscle that is the largest and strongest part of the four rotator cuff muscles. It is located in the subscapular fossa of the scapula, attaching between the scapula and the proximal humerus. The subscapularis muscle is innervated by both the upper and lower subscapular nerves (C5-C6), which are branches of the posterior cord of the brachial plexus. The upper subscapular nerve supplies the upper part of the subscapularis, while the lower subscapular nerve branches into two, with one branch supplying the lower part.
The primary function of the subscapularis muscle is the internal rotation of the humerus, which is the upper arm bone. It helps in shoulder adduction and extension, particularly when the arm is raised, as it pulls the humerus forward and downward. The subscapularis also plays a crucial role in stabilising the shoulder joint by contributing to the fixation of the proximal humerus during movements of the elbow, wrist, and hand. This stabilisation helps to prevent injuries, such as shoulder dislocations, which commonly occur when the humerus slides inferiorly through the unprotected part of the joint.
The subscapularis muscle is susceptible to injuries, especially in athletes who participate in throwing sports. Subscapularis tendonitis can cause pain when moving the shoulder, especially when the arm is raised above the shoulders. Overuse of the subscapularis muscle can lead to a feeling of inability to lift the arm, and it may even be responsible for a frozen shoulder. The established clinical test for examining the subscapularis muscle is the Gerber Lift-off test, also known as Gerber's test or the \"lift-off\" test. The bear hug test, which involves internal rotation while the palm is held on the opposite shoulder and the elbow is in a position of maximal anterior translation, is also used to evaluate the subscapularis muscle for tears.
The primary blood supply to the subscapularis muscle is the subscapular artery, a branch of the axillary artery. The subscapularis tendon lies approximately 3 to 5 cm under the surface, which can be challenging for ultrasonography examinations. However, the use of a highly penetrative 5 MHz linear applicator can facilitate a detailed examination of the muscle.
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Innervation and functions
The rotator cuff is a group of four muscles and tendons that attach to the shoulder bones. These muscles are the supraspinatus, infraspinatus, teres minor, and subscapularis. The rotator cuff muscles are responsible for the internal and external rotation of the arm in the shoulder joint. They also function to stabilize and centre the humeral head in the glenoid cavity, tightening the joint capsule and preventing a pinch during shoulder movements.
The supraspinatus muscle allows for the rotation and lifting of the arm. It stretches from the top of the scapula to the upper end of the humerus. The subscapularis muscle is important for holding the arm outstretched, away from the body, and for internal rotation of the humerus. The teres minor muscle is responsible for the external rotation and adduction of the arm. The supraspinatus muscle initiates the abduction of the arm.
The rotator cuff muscles arise from the scapula and connect to the head of the humerus, forming a cuff around the glenohumeral joint. The rotator cuff compresses the glenohumeral joint during abduction of the arm, an action known as concavity compression, allowing the deltoid muscle to further elevate the arm. The rotator cuff muscles also provide stability to the glenohumeral joint by preventing the sliding of the head of the humerus during arm movements, allowing for a full range of motion.
The vascular supply to the rotator cuff muscles is mainly via the suprascapular artery, the subscapular artery, and the posterior circumflex humeral artery. The suprascapular nerve is also involved in the innervation of the rotator cuff.
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Frequently asked questions
The rotator cuff is a group of muscles and tendons that act to stabilise the human shoulder and allow for its extensive range of motion.
The rotator cuff consists of four muscles: the supraspinatus, infraspinatus, teres minor, and subscapularis.
The supraspinatus muscle allows you to rotate and lift your arm. It also initiates the abduction of the arm.
The subscapularis muscle lets you hold your arm outstretched, away from your body. It is also important for the internal rotation of the humerus.
Rotator cuff tendinitis refers to inflammation of the tendons of the rotator cuff muscles. This usually occurs due to repetitive use of the shoulder joint.
