Rotator Cuff Muscles Anatomy

Location & Overview

The rotator cuff refers to a collection of muscles in the shoulder that primarily provide stability to the glenohumeral joint. The head of the humerus is a large, spherical head that fits inside a cavity called the glenoid cavity. The head of the humerus and the glenoid cavity form the glenohumeral joint. The rotator cuff is composed of the following four muscles: the supraspinatus, infraspinatus, teres minor, and subscapularis. A useful mnemonic for memorizing these muscles is ‘SITS’.^[1,2]

All four of the rotator cuff muscles connect the scapula to the humerus. The glenoid cavity is a part of the scapula, and the head of the humerus is located at the top of the humerus. The rotator cuff muscles’ tendons blend with the joint capsule. These tendons form a musculotendinous collar, which surrounds the superior, posterior, and anterior portions of the joint. The inferior part of the joint does not have a musculotendinous collar, and because of this, the inferior portion is unprotected. Consequently, the inferior and anterior-inferior region is relatively vulnerable, and many shoulder dislocations occur anteriorly or anteroinferiorly.^[1,2]

Some fibers of the teres minor muscle interlock and connect with those of the infraspinatus. The supraspinatus and subscapularis tendons also interlock and connect, and they envelop part of the biceps tendon.^[3]

Origin & Insertion

The supraspinatus originates at the supraspinous fossa of the scapula. It then passes under the acromion and above the glenohumeral joint to insert on the greater tubercle of the humerus (superior aspect).^[1,4,2]

The infraspinatus originates at the infraspinous fossa of the scapula. It then inserts on the greater tubercle of the humerus (posterior aspect), just inferior to the insertion of the supraspinatus.^[1,5,2]

The teres minor originates on the lateral border of the scapula and then inserts on the greater tubercle of the humerus (inferior aspect), just inferior to the insertion of the infraspinatus.^[1,6,2]

The subscapularis is the only rotator cuff muscle originating on the anterior side of the scapula. It originates at the subscapular fossa and then inserts on the lesser tubercle of the humerus.^[1,7,2]

Actions

The primary role of all of the rotator cuff muscles is to stabilize the head of the humerus in the glenoid cavity. This stabilization is achieved by compressing the head of the humerus against the glenoid.^[1,2]

The supraspinatus is responsible for shoulder abduction. The supraspinatus is the primary mover during the first 0 to 15 degrees of shoulder abduction. After the first 0 to 15 degrees, the deltoid muscle is then mainly responsible for shoulder abduction. It also contributes weakly to the lateral rotation of the humerus in certain positions.^[1,4,2]

The infraspinatus is responsible for lateral rotation of the shoulder (also known as external rotation).^[1,5,2]

The teres minor is also responsible for lateral rotation of the shoulder (also known as external rotation).^[1,6,2]

The subscapularis muscle is responsible for medial rotation of the shoulder (also known as internal rotation).^[1,7,2]

In addition to the primary actions of the rotator cuff muscles mentioned above, the teres minor and subscapularis have also been demonstrated to provide very weak assistance during shoulder adduction.^[7,2]

Innervation

The infraspinatus and supraspinatus are innervated by the suprascapular nerve (C5, C6). The suprascapular nerve originates from the superior trunk of the brachial plexus and passes through the suprascapular foramen.^[1,4,5]

The teres minor is innervated by the axillary nerve (C5, C6). The axillary nerve originates from the posterior cord of the brachial plexus and passes through the quadrangular space into the posterior scapular region.^[1,6]

The upper and lower branches of the subscapular nerve (C5, C6, C7) innervate the subscapularis muscle. This nerve originates from the posterior cord of the brachial plexus.^[1,7]

Blood Supply

Blood is supplied to the supraspinatus and infraspinatus muscles via the suprascapular artery. The suprascapular artery is usually a branch of the thyrocervical trunk, which is a major branch of the subclavian artery. The suprascapular artery travels laterally from the neck toward the posterior scapular region, passing near the suprascapular notch or foramen.^[1] The infraspinatus also receives blood from the circumflex scapular artery. The circumflex scapular artery passes around the lateral border of the scapula and enters the infraspinous fossa.^[5]

The teres minor receives its blood supply via the subscapular artery, the circumflex scapular artery, and the posterior circumflex humeral artery. The circumflex scapular artery is a branch of the subscapular artery. The subscapular artery and the posterior circumflex humeral artery both arise from the third and most distal part of the axillary artery. The axillary artery travels along the inferior margin of the subscapularis muscle.^[6]

The subscapularis muscle receives its blood supply via the subscapular artery. The subscapular artery is the largest branch of the axillary artery. The subscapular artery originates from the third part of the axillary artery. The axillary artery travels along the inferior margin of the subscapularis muscle and divides into the circumflex scapular artery and the thoracodorsal artery.^[1]