Reading

Body Surface

The primary surface landmarks of the shoulder and posterior arm are associated with the skull (external occipital protuberance), spine (spinous process C7), scapula (spine and acromion), humerus (medial and lateral epicondyles), ulna (olecranon), and the triceps brachii tendon. The skin overlying the shoulder and posterior arm is innervated by the upper lateral cutaneous of the arm, posterior cutaneous of the arm and posterior cutaneous of the forearm nerves and cutaneous branches of dorsal rami C3, C4 and T2 – T7.

Skeleton and Joints

The bones and joints associated with the shoulder and posterior arm are 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 acromioclavicular joint moves during elevation and depression, protraction and retraction, and rotation of the scapula. The glenohumeral joint moves in flexion and extension, abduction and adduction, medial rotation and lateral rotation, and circumduction (combination of the other movements) of the arm. The elbow joint moves in flexion and extension and contributes to pronation and supination of the forearm.

Fascial Organization

The shoulder region refers to the (posterior) muscles that pass between the scapula and proximal humerus plus muscles passing from the trunk to the scapula or humerus (superficial muscles of the back). The deltoid fascia is continuous with the pectoral, brachial and infraspinatus fasciae. The infraspinatus fascia is thick and obscures the border between the infraspinatus and deltoid muscles. 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 superficial muscles of the back and shoulder are active in elevation ( trapezius and levator scapulae), retraction (trapezius and rhomboids) and rotation (trapezius) of the scapula, and extension, adduction and medial rotation of the shoulder joint ( latissimus dorsi). The shoulder muscles are active in flexion ( deltoid), extension (deltoid), abduction (deltoid and supraspinatus), adduction ( teres major), medial rotation (deltoid and teres major) and lateral rotation (deltoid, infraspinatus and teres minor) of the shoulder joint. The muscles of the posterior compartment of the arm are active in extension ( long head of triceps brachii) of the shoulder joint and extension (long, lateral and medial head of triceps brachii) of the forearm.

Innervation

The accessory (trapezius), dorsal scapular (levator scapulae and rhomboids), suprascapular (infraspinatus and supraspinatus), axillary (deltoid and teres minor), thoracodorsal (latissimus dorsi) and lower subscapular (teres major) nerves innervate the shoulder muscles. The radial nerve innervates the muscles of the posterior compartment of the arm.

Blood Supply

Branches of the transverse cervical, suprascapular, subscapular and posterior circumflex humeral arteries supply the muscles of the shoulder. Branches of the profunda brachii and posterior circumflex humeral artery supply the muscles of the posterior compartment of the arm.

Anatomical Spaces or Features

There are three anatomical spaces associated with the shoulder and posterior compartment of the arm. The teres minor ( superior), teres major ( inferior), long head of the triceps ( medial) and surgical neck of the humerus ( lateral) bound the quadrangular space. The axillary nerve and posterior circumflex humeral vessels traverse the quadrangular space. The triangular space is bounded by the teres minor ( superior), teres major ( inferior) and long head of the triceps ( lateral). The circumflex scapular artery and vein traverse this space. The teres major (superior), long head of the triceps (medial) and shaft of the humerus (lateral head of the triceps; lateral) bound the triangular interval (lower triangular space). The radial nerve and profunda brachii (or radial and middle collateral) artery traverse this space.