The wrist is a complex joint connecting the forearm to the hand. This intricate design allows for a wide array of movements, making it a fundamental component for all daily activities. Its precise arrangement of bones and soft tissues facilitates both strength and dexterity.
The Bones of the Wrist
The wrist is not a single bone, but a collection of eight small bones known as the carpal bones. These bones are arranged into two distinct rows, forming the flexible foundation of the hand. They articulate with the forearm bones (radius and ulna) and the hand’s metacarpals.
The proximal row, closer to the forearm, includes four bones: the scaphoid, lunate, triquetrum, and pisiform. The scaphoid bone, sometimes called the navicular bone of the hand, is boat-shaped and is the largest bone in this row, located on the thumb side of the wrist. The lunate bone, also known as the semilunar bone, has a crescent or moon-like shape. The triquetrum, also referred to as the triquetral bone or triangular bone, is pyramid-shaped and sits on the pinky finger side. The pisiform bone is a small, pea-shaped bone that rests on the triquetrum.
The distal row, closer to the hand, also comprises four bones: the trapezium, trapezoid, capitate, and hamate. The trapezium, or greater multangular bone, is found at the base of the thumb and is crucial for thumb movement. Adjacent to the trapezium, the trapezoid bone, also known as the lesser multangular bone, is a small, wedge-shaped bone. The capitate bone, often called the os magnum, is the largest carpal bone and occupies a central position within the wrist. The hamate bone, also known as the unciform bone, is wedge-shaped and features a distinctive hook-like projection on its palm-facing side.
How Wrist Bones Work
The eight carpal bones allow for a remarkable range of motion at the wrist joint. They articulate with each other and with the forearm and hand bones, enabling movements like flexion, extension, and side-to-side deviation. These combined movements also allow for circumduction, a circular motion of the hand. Beyond facilitating movement, the carpal bones provide a stable platform for the hand. Supported by numerous ligaments, their interconnectedness contributes to both flexibility and strength. This structural integrity transmits forces essential for gripping and manipulating objects.
Common Wrist Issues
The wrist’s complex structure and frequent use make its bones susceptible to various issues. Fractures, often from falls onto an outstretched hand, can occur, with the scaphoid bone being particularly prone due to its limited blood supply, which can make healing challenging. Ligament sprains result from excessive force or sudden movements, stretching or tearing these connections. Over time, osteoarthritis can develop in the joints between carpal bones, leading to pain and stiffness in the wrist. Carpal tunnel syndrome, while primarily affecting nerves and tendons, involves the carpal bones forming the tunnel’s boundaries.