The Rotator Cuff is a group of muscles in the shoulder that allow a wide range of movement while maintaining the stability of the glenohumeral joint. The rotator cuff includes the following muscles[rx][rx][rx]:
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Subscapularis
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Infraspinatus
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Supraspinatus
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Teres minor
A helpful mnemonic to remember these muscles is “SITS.”
The glenohumeral joint is a ball and socket joint and comprises a large spherical humeral head and a small glenoid cavity. This anatomy makes the joint highly mobile, however, really unstable. Stabilization in the shoulder is provided collectively by the non-contractile tissue of the glenohumeral joint (static stabilizers) such as the capsule, the labrum, the negative intraarticular pressure and the glenohumeral ligaments; and the contractile tissues (dynamic stabilizers) such as the rotator cuff and the long head of the biceps brachii.
Structure of The Rotator Cuff
The primary biomechanical role of the rotator cuff is to stabilize the glenohumeral joint by compressing the humeral head against the glenoid. These four muscles arise from the scapula and insert into the humerus. The tendons of the rotator cuff muscles blend with the joint capsule and form a musculotendinous collar that surrounds the posterior, superior, and anterior aspects of the joint, leaving the inferior aspect unprotected. This arrangement is an important factor since most of the shoulder luxations occur because the humerus slides inferiorly through the unprotected part of the joint. During arm movements, the rotator muscles contract and prevent the sliding of the head of the humerus, allowing full range of motion and providing stability.
Additionally, rotator cuff muscles help in the mobility of the shoulder joint by facilitating abduction, medial rotation, and lateral rotation.
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Subscapularis: Medial (internal) rotation of the shoulder
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Supraspinatus: Abduction of the arm – Necessary for the initial 0 to 15 degrees of shoulder abduction motion. The deltoid muscle abducts the arm beyond 15 degrees
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Infraspinatus: Lateral (external) rotation of the shoulder
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Teres Minor: Lateral (external) rotation of the shoulder
During the physical examination, each muscle can undergo independent evaluation based on the specific movement of each muscle.
Blood Supply of The Rotator Cuff
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 artery – is a branch of the thyrocervical trunk (a major branch of the subclavian artery) and originates at the base of the neck. It enters the posterior scapular region superior to the suprascapular foramen (the nerve passes through the foramen) and supplies the supraspinatus and infraspinatus muscles.
The subscapular artery – is the largest branch of the axillary artery. It originates from the third part of the axillary artery, follows the inferior margin of the subscapularis muscle, and then divides into the circumflex scapular artery and the thoracodorsal artery. It gives vascular supply to the subscapularis muscle.
The posterior circumflex humeral artery – originates from the third part of the axillary artery in the axilla. It enters the posterior scapular region through the quadrangular space (accompanied by the axillary nerve) and supplies the teres minor muscle.
All lymphatics from the upper limb drain into lymph nodes in the axilla.
Nerves of The Rotator Cuff
The subscapular nerve (upper and lower branches) innervates the subscapularis muscle.
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Originate from the posterior cord of the brachial plexus
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C5, C6, C7
The suprascapular nerve innervates the infraspinatus and supraspinatus
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Originates from the superior trunk of the brachial plexus
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Passes through the suprascapular foramen
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C5 and C6
The axillary nerve innervates teres minor
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Originates from the posterior cord of the brachial plexus
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Passes through the quadrangular space into the posterior scapula region
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C5 and C6
Muscles Attachment of The Rotator Cuff
The subscapularis is the largest component of the posterior wall of the axilla. It prevents the anterior dislocation of the humerus during abduction and medially rotates the humerus. A large bursa separates the muscle from the neck of the scapula.[rx]
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Origin: subscapular fossa of the scapula
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Insertion: lesser tubercle of the humerus
The supraspinatus muscle is the only muscle of the rotator cuff that is not a rotator of the humerus.
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Origin: supraspinous fossa of the scapula
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Passes above the glenohumeral joint
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Insertion: greater tuberosity of the humerus
The infraspinatus is a powerful lateral rotator of the humerus. The tendon of this muscle is sometimes separated from the capsule of the glenohumeral joint by a bursa.
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Origin: infraspinous fossa of the scapula
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Insertion: greater tuberosity of the humerus, immediately below the supraspinatus.
The teres minor is a narrow and long muscle entirely covered by the deltoid, hardly differentiated from the infraspinatus.
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Origin: lateral border of the scapula (below the infraglenoid tubercle)
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Insertion: greater tuberosity of the humerus, below the infraspinatus tendon.
The intrinsic muscles of the shoulder connect the scapula and/or clavicle to the humerus. These include[rx]
Deltoid
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Origin: Lateral clavicle, acromion and scapular spine
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Insertion: Deltoid tuberosity
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Innervation: Axillary nerve (C5, C6)
Teres major
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Function: Adduction and medial rotation of the arm
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Origin: Posterior surface of the scapula at its inferior angle
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Insertion: Intertubercular groove of the proximal humerus on its medial aspect
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Innervation: Lower scapular nerve (C5, C6)
Supraspinatus (Rotator Cuff)
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Function: Initiation of arm abduction (first 15 degrees), stabilize glenohumeral joint
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Origin: Posterior scapula, superior to the scapular spine/supraspinous fossa
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Insertion: Top of the greater tubercle of the humerus
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Innervation: Suprascapular nerve (C5, C6)
Infraspinatus (Rotator Cuff)
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Function: Lateral rotation of the arm, stabilize glenohumeral joint
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Origin: Posterior scapula, inferior to the scapular spine/Infraspinous fossa
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Insertion: Greater tubercle of the humerus, between the supraspinatus and teres minor insertion
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Innervation: Suprascapular nerve (C5, C6)
Teres minor (Rotator Cuff)
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Function: Lateral rotation of the arm, stabilize glenohumeral joint
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Origin: Inferior angle of the scapula
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Insertion: Inferior aspect of the greater tubercle
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Innervation: Axillary nerve (C5, C6)
Subscapularis (Rotator Cuff)
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Function: Adduction and medial rotation of the arm, stabilize glenohumeral joint
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Origin: Anterior aspect of the scapula
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Insertion: Lesser tubercle of the humerus
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Innervation: Subscapular nerves (C5, C6, C7)
Other muscles that affect movement at the shoulder joint include:
Trapezius
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Function:
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Upper fibers elevate the scapula and rotate it during abduction of the arm (90 to 180 degrees)
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Middle fibers retract the scapula
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Lower fibers pull the scapula inferiorly.
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Origin: Skull, nuchal ligament and the spinous processes of C7 to T12
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Insertion: clavicle, acromion and the scapular spine
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Innervation: Accessory nerve (C5, C6)
Latissmus dorsi
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Function: Extends, adducts and medially rotates the upper limb
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Origin: Spinous processes of T6 to T12, iliac crest, thoracolumbar fascia, and the inferior three ribs
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Insertion: Intertubercular sulcus of the humerus
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Innervation: Thoracodorsal nerve (C6, C7, C8)
Levator scapulae
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Function: Elevates the scapula
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Origin: Transverse processes of the C1 to C4 vertebrae
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Insertion: Medial border of the scapula
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Innervation: Dorsal scapular nerve (C5)
Rhomboid major
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Function: Retracts and rotates the scapula
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Origin: Spinous processes of T2 to T5 vertebrae
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Insertion: Inferomedial border of the scapula
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Innervation: Dorsal scapular nerve (C5)
Rhomboid minor
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Function: Retracts and rotates the scapula
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Origin: Spinous processes of C7 to T1 vertebrae
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Insertion: Medial border of the scapula
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Innervation: Dorsal scapular nerve (C5)
Serratus anterior
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Function: fixes the scapula into the thoracic wall, and aids in rotation and abduction of the arm (90 to 180 degrees)
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Origin: Surface of the upper eight ribs at the side of the chest
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Insertion: Along the entire anterior length of the medial border of the scapula
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Innervation: Long thoracic nerve (C5, C6, C7)
Pectoralis major
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Function:
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Clavicular head flexes and adducts arm
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Sternal head adducts and medially rotates the arm
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Accessory for inspiration
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Origin:
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Clavicular head: medial half clavicle
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Sternocostal head: Lateral manubrium and sternum, six upper costal cartilages and external oblique aponeurosis
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Insertion: Intertubercular groove of the proximal humerus on its lateral aspect
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Innervation: Medial and lateral pectoral nerves (C6, C7, C8)
Pectoralis minor
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Function: Depression of the shoulder, protraction of the scapula
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Origin: Third, fourth, fifth ribs close to their respective costal cartilages
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Insertion: Coracoid process
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Innervation: Medial pectoral nerve (C8, T1)
Subclavius
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Function: Depression and stabilization of the clavicle
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Origin: First rib medially
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Insertion: Middle of the clavicle, inferiorly
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Innervation: Nerve to subclavius (C5, C6)
Coracobrachialis
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Function: Flexion and adduction of the arm
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Origin: Coracoid process
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Insertion: Middle of the humerus, on its medial aspect
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Innervation: Musculocutaneous nerve (C5, C6, C7)
Biceps brachii
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Function: Resists dislocation of the shoulder, flexion of the forearm, supination of the forearm
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Origin:
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Short head: coracoid process
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Long head: supraglenoid tubercle of the scapula and superior labrum
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Insertion: Radial tuberosity of radius and forearm fascia (as bicipital aponeurosis)
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Innervation: Musculocutaneous nerve (C5, C6)
Triceps brachii
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Function: Resists dislocation of the shoulder, major extensor of the forearm
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Origin:
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Lateral head: above the radial groove of the humerus,
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Medial head: below the radial groove of the humerus
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Long head: infraglenoid tubercle of the scapula
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Insertion: Olecranon process of ulna and forearm fascia
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Innervation: Radial nerve (C6, C7, C8)
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