Anatomy Of The Upper LimbEdit

The upper limb is a highly specialized complex designed for reach, grasp, and fine manipulation. It extends from the shoulder girdle, incorporating the shoulder joint and its surrounding muscles, through the arm and forearm to the hand. Its architecture—bones, joints, muscles, nerves, and vessels—works together to provide a wide range of motion, strength, and dexterity in everyday tasks, manual labor, and sport. Key components are the clavicle and scapula of the shoulder girdle, the humerus of the arm, the radius and ulna of the forearm, and the carpal, metacarpal, and phalangeal bones of the hand. This article surveys the major structures and their relationships, with attention to function and common clinical considerations.

Skeletal framework

Bones of the upper limb

The shoulder girdle consists of the clavicle clavicle and the scapula scapula.
The long bone of the arm is the humerus humerus.
The forearm contains two parallel bones: the radius radius and the ulna ulna.
The hand is built from wrist bones (the carpals carpal bones), the long bones of the palm (the metacarpals metacarpals), and the bones of the fingers (the phalanges phalanges).

Carpal bones are arranged in two rows and include the scaphoid, lunate, triquetrum, and pisiform in the proximal row, with the trapezium, trapezoid, capitate, and hamate in the distal row. These small bones create a flexible, yet sturdy, carpal arch that supports wrist motion and load transfer to the forearm.

Joints and articulations

The shoulder joint, the glenohumeral joint glenohumeral joint, is a ball-and-socket articulation allowing remarkable motion in multiple planes.
The sternoclavicular and acromioclavicular joints stabilize the shoulder girdle and permit transmission of movements to the trunk.
The elbow complex includes the humeroulnar and humeroradial joints, with radioulnar joints facilitating forearm rotation.
Distal radioulnar articulations and the radiocarpal (wrist) joint connect the forearm to the hand, enabling hand positioning relative to the forearm. These joints are reinforced by ligaments, articular capsules, and surrounding musculotendinous contributions.

Muscular architecture

Shoulder girdle and proximal muscles

The rotator cuff comprises the supraspinatus, infraspinatus, teres minor, and subscapularis, stabilizing the glenohumeral joint and guiding its rotation. The rotator cuff muscles work with the deltoid and the pectoral and scapular stabilizers to position the arm.
Major movers include the deltoid, pectoralis major, latissimus dorsi, and teres major, which power arm elevation, adduction, rotation, and extension.
The trapezius and serratus anterior coordinate scapular motion, enabling full arm reach.

Arm muscles

Anterior compartment: biceps brachii, brachialis, and coracobrachialis. These muscles mainly flex the elbow and contribute to forearm supination (biceps) or act as elbow flexors (brachialis, coracobrachialis).
Posterior compartment: triceps brachii (long, lateral, and medial heads) extends the elbow and supports shoulder extension in certain positions.

Forearm muscles

Anterior (flexor-pronator) compartment: flexors of the wrist and fingers, such as flexor carpi radialis, flexor carpi ulnaris, flexor digitorum superficialis and profundus, flexor pollicis longus, and pronator teres.
Posterior (extensor) compartment: extensors of the wrist and fingers, such as extensor carpi radialis, extensor carpi ulnaris, extensor digitorum, and the extensor pollicis muscles.
Forearm muscles also contribute to pronation and supination via the pronator teres, pronator quadratus, and supinator.

Hand muscles

The intrinsic muscles of the hand include the thenar muscles (thumb side), the hypothenar muscles (little finger side), the lumbricals, and the interossei. These muscles fine-tune grip, finger opposition, and coordinated finger movements.
The intrinsic muscles work in concert with the extrinsic tendons that originate in the forearm to execute complex hand function.

Neurovascular supply

Nerves

The brachial plexus gives rise to the major nerves supplying the upper limb: the musculocutaneous, axillary, radial, median, and ulnar nerves. These nerves provide motor and sensory innervation to regions along the arm, forearm, and hand.
Musculocutaneous nerve supplies the anterior arm muscles and sensory input to the lateral forearm.
Axillary nerve innervates the deltoid and teres minor, with cutaneous input over part of the shoulder.
Radial nerve supplies the posterior compartments of the arm and forearm and sensory input to the dorsal hand.
Median nerve supplies most of the anterior forearm muscles and many intrinsic hand muscles, with sensory input to the palmar aspects of the lateral hand.
Ulnar nerve innervates the medial forearm muscles and many intrinsic hand muscles, with sensory input to the medial hand.

Vessels

The axillary artery and its branches supply the shoulder region, while the brachial artery travels down the arm, giving off the profunda brachii and continuing as the radial and ulnar arteries to the forearm and hand.
Venous drainage parallels the arterial pattern, returning blood via the subclavian and into the central circulation.

Functional compartments and biomechanics

The shoulder girdle and girdle-associated muscles enable a wide arc of motion at the glenohumeral joint, essential for reaching, throwing, and overhead activities.
The arm’s anterior and posterior compartments allow strong elbow flexion and extension, providing the necessary leverage for lifting and manipulating objects.
The forearm functions as a sophisticated fulcrum for hand positioning, with pronation and supination enabling precise orientation of the palm for grasping.
The hand’s intrinsic and extrinsic musculature combine to perform fine motor tasks, from a delicate pinch to a powerful grip.

Development and variation

Upper limb development follows a coordinated program during embryogenesis, with bone formation, joint development, and muscle differentiation shaping the mature limb.
Anatomical variations occur in individuals, including accessory muscles, bone shape differences, and nerve branching patterns. Clinicians recognize these variations in imaging, surgery, and rehabilitation to optimize outcomes.

Pathology and clinical relevance

Common injuries include rotator cuff tears, dislocations of the glenohumeral joint, fractures of the clavicle or humerus, and forearm fractures that affect the radius or ulna.
Nerve injuries along the upper limb, such as radial nerve palsy or carpal tunnel syndrome (median nerve compression at the wrist), present with characteristic motor and sensory deficits and require timely evaluation.
Vascular considerations include arterial injury or compression in the shoulder region, which can compromise limb perfusion if not promptly addressed.
Understanding the regional anatomy aids in physical examination, imaging interpretation, surgical planning, and rehabilitation strategies for restoring function after injury or disease.