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Upper Limb AnatomyEdit

The upper limb is a complex and highly adaptable region that spans from the trunk to the fingers. It is built for both strength and dexterity, enabling actions as varied as heavy lifting, precise manipulation, and delicate tactile exploration. The architecture of the shoulder girdle, arm, forearm, wrist, and hand depends on a coordinated interplay among bones, joints, muscles, tendons, nerves, and blood vessels, all of which transmit forces and signals from the body to the outside world. The clavicle serves as the sole bony bridge between the upper limb and the axial skeleton, while the scapula slides along the thoracic wall to permit a remarkable range of motion at the shoulder joint.

Throughout the upper limb, stability is balanced with mobility. The arrangement of joints—most notably the glenohumeral joint in the shoulder, the elbow joint, and the radioulnar articulations—allows both powerful extension and fine, controlled movements. The nervous and vascular networks run in close association with muscular and fascial compartments, ensuring rapid innervation and robust blood supply to muscle groups and to the skin of the limb. The hand, with its intricate array of bones and muscles, completes the chain by translating proximal motion into precise, individualized grip and finger function.

With that backdrop, this article surveys the major bones, joints, muscles, nerves, and vessels that compose the upper limb, along with the functional principles that underlie everyday movement and common clinical concerns. For readers seeking more detail on related regions or systems, bones, muscles, and nerves provide foundational concepts, while region-specific terms connect this article to broader anatomical discussion.

Skeletal framework

  • Shoulder girdle

    • The clavicle and scapula form the shoulder girdle, providing the base from which the upper limb operates. The clavicle acts as a strut that keeps the limb away from the thorax and transmits forces from the arm to the trunk. The scapula glides across the posterior thorax, enabling elevation, depression, protraction, retraction, and rotation.
    • Key surface features include the acromion, coracoid process, glenoid cavity, and the scapular spine, each serving as attachment points for muscles and as leverage for movement. The glenoid fossa accommodates the head of the humerus to form the main shoulder joint.

  • Arm and forearm bones

    • The upper arm contains the humerus, the long bone that extends from the shoulder to the elbow. Its proximal end articulates with the glenoid cavity, while its distal end forms part of the elbow joint.
    • The forearm comprises two parallel bones, the radius and the ulna. The radius crosses over the ulna during rotation, enabling pronation and supination of the forearm.
    • The distal radioulnar joint, along with the radiocarpal joint in the wrist, completes the continuum from shoulder to hand.

  • Wrist and hand bones

    • The wrist contains the eight carpal bones arranged in two rows, permitting a blend of stability and flexibility for cupping, pinching, and fine manipulation.
    • The metacarpal bones form the framework of the palm, while the phalanges constitute the fingers, including proximal, middle, and distal segments that enable precise grip and dexterous tasks.
    • Together, the carpal, metacarpal, and phalangeal bones support a wide array of grips—from powerful grasp to delicate fingertip control.

Joints and movements

  • Shoulder joint complex

    • The glenohumeral joint is a ball-and-socket articulation between the head of the humerus and the glenoid cavity of the scapula. It provides the largest range of motion of any joint in the body, allowing flexion, extension, abduction, adduction, internal rotation, external rotation, and circumduction.
    • Stability is provided by a surround of muscles and tendons, notably the rotator cuff tendons, which reinforce joint stability while permitting mobility.
    • The acromioclavicular joint and sternoclavicular joint connect the shoulder girdle to the trunk and contribute to the overall mobility and positioning of the limb.

  • Elbow and forearm joints

    • The elbow comprises the hinge-like humeroulnar joint and the humeroradial joint, permitting flexion and extension, with the proximal radioulnar joint enabling pronation and supination of the forearm.
    • The interrelationship of radius and ulna during rotation underpins hand positioning in many tasks, from turning a doorknob to writing.

  • Wrist and hand joints

    • The radiocarpal joint links the distal radius to the proximal row of carpal bones, supporting complex wrist movements in multiple directions.
    • Intercarpal joints between adjacent carpal bones, and the carpometacarpal and metacarpophalangeal joints, contribute to the hand’s versatility, while the interphalangeal joints enable flexion and extension of the digits.

Muscles

Nerves, vessels, and innervation

  • The upper limb’s motor and sensory innervation primarily follows the brachial plexus, a network that gives rise to the major nerves of the arm. Key branches include the musculocutaneous nerve, which innervates many forearm flexors; the axillary nerve, which supplies part of the deltoid and the skin over the shoulder; the radial nerve and ulnar nerve, which serve the posterior and many intrinsic hand muscles, and the median nerve, which supplies most of the flexor forearm muscles and several hand muscles.
  • Blood supply is organized around the axillary artery and its branches, with continuation as the brachial artery in the arm, and distal branches such as the radial artery and ulnar artery supplying the forearm and hand.
  • Venous drainage mirrors arterial routes, with major superficial and deep channels returning blood to the central circulation. Lymphatics draining the upper limb accompany the deep and superficial venous systems to regional nodes.

Functional anatomy and biomechanics

  • The architecture of the upper limb supports a broad spectrum of tasks, from heavy lifting to fine manipulation. The shoulder’s wide range of motion is balanced by muscular stabilization to avoid dislocation during active use. The hand’s dexterity depends on the coordinated action of extrinsic forearm muscles and intrinsic hand muscles, enabling grasp patterns such as power grip and precision grip.
  • Biomechanically, the limb functions as a kinetic chain: proximal stability from the shoulder girdle supports distal mobility at the hand. Joint morphology and muscle attachments provide torque and control across multiple planes of movement, while tendons, fasciae, and retinacula maintain efficiency and force transmission.

Clinical relevance

  • Common injuries of the upper limb include dislocations of the shoulder, degenerative or inflammatory problems of the rotator cuff, and fractures of the clavicle or humerus. Distal radius fractures, particularly in the elderly, are frequent and have implications for distal nerve and vascular structures as well as wrist function.
  • Nerve entrapments, such as compression of the median nerve at the wrist (often discussed in the context of carpal tunnel syndrome), affect motor and sensory function in the hand. Ulnar nerve compression at the elbow or wrist can produce characteristic numbness and weakness in intrinsic hand muscles.
  • Vascular injuries in the limb are of concern in trauma and may compromise perfusion to muscles and skin, necessitating prompt assessment and repair when indicated.

See also