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Body Surface

The primary surface landmarks of the pectoral region, axilla and anterior arm are associated with the sternum (jugular notch), clavical, scapula (coracoid process and acromion), humerus (medial and lateral epicondyles), and anterior, medial and posterior axillary walls. The skin overlying the pectoral region, axilla and anterior arm is innervated by the intercostobrachial, medial cutaneous of the arm, upper lateral cutaneous of the arm, medial cutaneous of the forearm, lateral cutaneous of the forearm nerves, and cutaneous branches of ventral rami C4, T2, T3 and T4.

Skeleton and Joints

The bones and joints associated with the pectoral region, axilla and anterior arm are the sternum and clavicle articulating at the sternoclavicular joint, the clavicle and scapula articulating at the acromioclavicular joint, the scapula and humerus articulating at the shoulder (glenohumeral) joint and the humerus, radius and ulna articulating at the elbow joint. The sternoclavicular and acromioclavicular joints move during elevation and depression, protraction and retraction, and rotation of the scapula. The glenohumeral joint moves in flexion and extension, abduction and adduction, medial and lateral rotation, and circumduction (combination of the other movements) of the humerus. The elbow joint moves in flexion and extension and contributes to pronation and supination of the forearm.

Fascial Organization

The pectoral region is comprised of the two pectoral muscles and their associated fasciae. The pectoralis major is surrounded by a thin layer of deep fascia that is continuous with the fascia of the axilla. The pectoralis minor is encased in the clavipectoral fascia that descends from the clavicle and covers the axillary vessels and cords of the brachial plexus.

The axilla is a pyramid-shaped region passing between the upper thoracic wall and root of the neck, and the arm. The walls of the axilla are formed by the pectoralis major and minor ( anterior), the subscapularis, teres major and latissimus dorsi ( posterior), ribs, intercostal muscles and serratus anterior ( medial) and intertubercular sulcus of the humerus ( lateral). The axilla is traversed by the axillary artery and vein, and the brachial plexus distal to the clavicle. Within the proximal axilla, the axillary artery and vein, and cords of the brachial plexus are encased in a tube of deep fascia, the axillary sheath. The axillary sheath is continuous with the prevertebral fascia of the neck.

The deep fascia of the arm (brachial fascia) is continuous with the deep fascia of the pectoral and shoulder regions. It has two intermuscular septa that attach in part to the intertubercular sulcus of the humerus and subdivide the arm into anterior and posterior compartments. The lateral intermuscular septum gives partial attachment to the triceps, brachialis, brachioradialis and extensor carpi radialis longus muscles. The medial intermuscular septum gives partial attachment to the triceps and brachialis muscles.

Muscles

The pectoral muscles are active in flexion, adduction and medial rotation of the shoulder joint ( pectoralis major) and assist in depressing and protracting the scapula ( pectoralis minor). The axillary muscles are active in protraction and rotation of the scapula ( serratus anterior) and medial rotation of the shoulder joint ( subscapularis). The muscles of the anterior compartment of the arm are active in flexion ( biceps brachii long head, biceps brachii short head and coracobrachialis) and adduction (coracobrachialis) of the shoulder joint, and flexion (biceps brachii long head, biceps brachii short head and brachialis) and supination (biceps brachii) of the forearm.

Innervation

The lateral and medial pectoral nerves innervate the pectoral (major and minor) muscles. The musculocutaneous (coracobrachialis, biceps brachii long head, biceps brachii short head and brachialis) and radial (brachialis) nerves innervate the muscles of the anterior compartment of the arm.

Blood Supply

The pectoral branches of the thoracoacromial artery supply the pectoral muscles. Branches of the distal axillary, the brachial, and the proximal radial and ulnar arteries supply the anterior compartment of the arm.

Anatomical Spaces or Features

The quadrangular space is bounded by the teres minor and subscapularis (superior), teres major (inferior), long head of the triceps (medial) and surgical neck of the humerus (lateral). The axillary nerve and posterior circumflex humeral vessels traverse the quadrangular space.

The cubital fossa is the triangular shaped soft tissue space positioned anterior to the elbow. It is bounded by the pronator teres (medial) and brachioradialis (lateral) muscles. Its roof is the deep fascia of the forearm and the bicipital aponeurosis, and its floor is the brachialis and supinator muscles. The fossa is traversed by the median nerve, and the distal brachial and proximal radial and ulnar vessels.

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