Upper LimbEdit
The upper limb is a masterfully organized network of bones, joints, muscles, nerves, and vessels that enables a remarkable range of motion and strength. From the broad stability of the shoulder girdle to the fine dexterity of the fingers, this region supports both large-scale actions such as lifting and throwing and intricate tasks like gripping and manipulating small objects. The system’s design balances mobility with stability, relying on muscular control, flexible joints, and a rich neurovascular supply to coordinate movement, sensation, and endurance.
Anatomical overview of the upper limb spans four major segments: the shoulder girdle, the arm, the forearm, and the hand. Each segment contributes specific functions, yet they work as an integrated unit. The bones of the shoulder girdle—the clavicle and scapula—anchor the limb to the trunk, while the humerus forms the long bone of the upper arm. In the forearm, the radius (bone) and ulna enable varied rotational movements, and in the hand, the complex assembly of carpal bones, metacarpal bones, and phalanages allows both power and precision. The system is innervated primarily by the brachial plexus, with the major peripheral nerves—axillary nerve, musculocutaneous nerve, radial nerve, median nerve, and ulnar nerve—providing motor control and sensory input. The principal arteries begin with the subclavian and continue as the axillary artery and brachial artery, branching into the radial artery and ulnar artery to perfuse the limb.
Anatomy and regions
Pectoral girdle and shoulder region
The shoulder girdle comprises the clavicle and scapula, forming a flexible base for arm movement. The primary ball-and-socket articulation is the glenohumeral joint, which permits extensive motion in multiple planes but relies on soft-tissue restraints, such as the rotator cuff tendons and the glenohumeral ligaments, to maintain joint stability. The acromioclavicular and sternoclavicular joints add additional mobility and enable complex scapular motion that complements arm movements. The shoulder’s bony and soft-tissue architecture is critical for overhead activities, throwing, and weight bearing through the upper limb. See also shoulder.
Arm
The upper arm houses the humerus, which articulates proximally with the glenoid fossa of the scapula and distally with the elbow joint complex. The arm’s musculature is organized into compartments that move the elbow, forearm, and hand. The main nerve supplying the arm is the musculocutaneous nerve, with contributions from other branches of the brachial plexus guiding motor and sensory function. See also humerus and elbow.
Forearm
In the forearm, the paired bones radius (bone) and ulna enable pronation and supination, alongside flexion and extension at the wrist and elbow. An interosseous membrane links the two bones, stabilizing the forearm during rotation and load transfer. The nerves and vessels traveling in the forearm—especially the radial nerve and ulnar nerve—provide sensation and motor control to posterior and anterior compartments, respectively, and to the hand. See also forearm.
Hand and digits
The hand comprises three skeletal tiers: the carpal bones forming the wrist, the metacarpal bones forming the palm, and the phalanges forming the fingers. The intrinsic muscles of the hand (such as the thenar and hypothenar groups) enable precise grip and opposition, while the extrinsic muscles (in the forearm) power larger movements. The wrist and hand together support delicate manipulation, tactile exploration, and tool use. See also hand and opposition (hand).
Muscles and biomechanics
Extrinsic and intrinsic muscle groups
Muscles that act on the upper limb are organized into extrinsic groups, which originate outside the hand (in the trunk or forearm) and insert onto the hand to drive grip, pull, or release, and intrinsic groups, which are contained within the hand itself and provide fine motor control. The rotator cuff muscles—together with the deltoid and scapular stabilizers—regulate shoulder stability during arm movement. See also deltoid and rotator cuff.
Joints and motion
Key joints include the glenohumeral joint (shoulder), the elbow complex (humero-ulnar and radiocapitellar articulations), and the wrist (radiocarpal joint) with associated intercarpal joints. The hand’s joints—carpo-metacarpal, metacarpophalangeal, and interphalangeal—permit a spectrum from powerful grasp to precise fingertip control. Range of motion varies by joint and is constrained by ligaments, tendons, cartilage, and neuromuscular input. See also elbow, wrist, and hand.
Neurovascular supply
Nerves
The upper limb receives innervation primarily from the brachial plexus, whose roots, trunks, and branches give rise to the major nerves: axillary nerve, musculocutaneous nerve, radial nerve, median nerve, and ulnar nerve. These nerves provide motor control to the muscles of the shoulder, arm, forearm, and hand, and convey sensory information from the skin and joints. See also brachial plexus.
Vessels
Arterial supply follows a predictable cascade: the subclavian artery becomes the axillary artery at the lateral border of the first rib, which continues as the brachial artery in the arm and then branches into the radial artery and ulnar artery in the forearm. Venous drainage parallels the arteries, returning blood to the central circulation. See also arteries of the upper limb.
Development and evolution
The upper limb develops from the embryonic limb buds with coordinated patterning that establishes bone, muscle, nerve, and vascular formation. Evolutionarily, the upper limb shows a trend toward enhanced versatility in primates, enabling both locomotor adjustments and refined manual skills for tool use and signaling. See also human evolution.
Clinical significance and common conditions
The upper limb is subject to a broad spectrum of injuries and degenerative conditions, ranging from acute fractures to chronic tendinopathies and nerve compressions. Common examples include rotator cuff tears, dislocations of the glenohumeral joint, clavicle fractures, fractures of the humerus, distal radius fractures, and carpal tunnel syndrome. Management decisions often reflect a balance between surgical intervention and conservative therapy, based on patient factors and evidence from clinical trials. See also carpal tunnel syndrome, rotator cuff, and elbow injury.
Controversies and debates in the field typically revolve around timing and modality of treatment rather than basic anatomy. For instance, clinicians weigh early surgical repair against nonoperative management for certain rotator cuff injuries, or consider immobilization versus early mobilization after fractures. In carpal tunnel syndrome, debates persist about the thresholds for surgical decompression versus continued conservative care. While discussions can be vigorous in medical circles, practice tends to align with established guidelines and high-quality evidence aimed at optimizing function and minimizing long-term disability. See also orthopedic surgery and physical therapy.
Comparative anatomy and function
Across mammalian species, the upper limb exhibits a common structural plan: a pectoral girdle to anchor the limb, long bones for leverage, and a hand capable of diverse grips. The precise arrangement of bones, joints, and tendinous attachments underpins both gross motor tasks and fine motor skills, reflecting trade-offs between strength, stability, and precision. See also anatomy.
History of the upper limb study
Historical descriptions of the upper limb have evolved from early anatomical dissections to contemporary imaging and biomechanical modeling. Advances in radiography, ultrasound, CT, and MRI have deepened understanding of soft-tissue structures and dynamic function, informing better diagnostics and rehabilitation strategies. See also medical imaging.