The human skeleton is divided into two main parts: the axial skeleton and the appendicular skeleton. While the axial skeleton forms the central core of the body, the appendicular skeleton includes the bones of the limbs and their supporting girdles. The upper limbs are specifically designed for mobility, dexterity, and reaching, allowing humans to interact with their environment in complex ways. Each upper limb attaches to the trunk via the pectoral girdle, linking the arm, forearm, wrist, and hand into a coordinated structural chain.
The pectoral girdle connects each upper limb to the axial skeleton. It consists of two bones: the clavicle (collarbone) and the scapula (shoulder blade).
In anatomical terms, the "arm" refers strictly to the region between the shoulder and the elbow. This region contains a single long bone called the humerus. The proximal end features a rounded head that fits into the scapula, flanked by the greater tubercle and lesser tubercle for muscle attachments. The shaft of the humerus runs down to the distal end, where the trochlea and capitulum articulate with the bones of the forearm. A common clinical landmark is the surgical neck of the humerus, a frequent site of fractures that can risk damage to the adjacent axillary nerve.
The forearm spans from the elbow to the wrist and contains two parallel bones: the radius and the **ulna".
Together, these bones allow for supination (turning the palm upward) and pronation (turning the palm downward) as the radius crosses over the stationary ulna.
The hand is an engineering marvel containing 27 bones, divided into three distinct groups:
Movement in the upper limb depends on a series of synovial joints linking the skeletal segments. The glenohumeral (shoulder) joint offers the greatest range of motion but sacrifices stability. The elbow joint is a hinge joint allowing flexion and extension, reinforced by strong collateral ligaments. Further down, the radiocarpal (wrist) joint connects the forearm to the proximal carpal bones, permitting bending in multiple directions. Each of these junctions relies on joint capsules, synovial fluid, and surrounding muscles to maintain alignment during activity.
Upper limb injuries—ranging from clavicle fractures during difficult deliveries to distal radius fractures from falls—are common encounters in clinical practice. Midwives and nurses must be vigilant in assessing neurovascular status following any limb trauma. The classic assessment includes checking the pulse (radial or brachial), color, temperature, capillary refill, and nerve function (sensation and movement). Prompt identification of nerve compression or restricted blood flow prevents long-term ischemic damage or permanent disability.