The wrist connects the hand to the forearm. While often referred to as a single “wrist bone,” it is a complex anatomical structure composed of several smaller bones. This intricate arrangement allows for a broad range of movements.
The Bones That Make Up the Wrist
The wrist’s core is formed by eight small, irregularly shaped carpal bones. These bones are arranged into two distinct rows, contributing to flexibility and strength. The proximal row is closer to the forearm, while the distal row is closer to the hand.
The proximal row has four carpal bones, starting from the thumb side. The scaphoid is boat-shaped and lies beneath the thumb. Next to the scaphoid is the lunate, crescent-shaped and positioned centrally. The triquetrum, a pyramidal, is on the pinky finger side, articulating with the lunate. Finally, the pisiform, a small pea-shaped, sits on the front surface of the triquetrum.
The distal row also contains four carpal bones, continuing from the thumb side. The trapezium, a multi-faceted, is positioned at the base of the thumb. Adjacent to the trapezium is the trapezoid, the smallest in the distal row. The capitate is the largest carpal, centrally located and somewhat head-shaped. Lastly, the hamate, characterized by a hook-like projection, is found on the pinky finger side of the wrist.
The Wrist’s Place in the Arm and Hand
The carpal bones form a crucial bridge connecting the forearm to the hand. The proximal carpal bones articulate directly with the forearm’s two long bones: the radius and the ulna. The radius, on the thumb side, bears the majority of the load at the wrist joint. It connects primarily with the scaphoid and lunate bones.
The ulna, on the pinky finger side, does not directly articulate with the carpal bones like the radius. Instead, a fibrous disc, the triangular fibrocartilage complex, separates the ulna from the carpal bones. This arrangement allows for complex rotational movements of the forearm and contributes to wrist stability.
The distal carpal bones connect to the five metacarpal bones, which form the hand’s framework. Each metacarpal extends from a carpal bone to form the palm and connect to the fingers. This network of articulations creates the versatile wrist joint. The wrist’s ability to move in multiple directions—flexion, extension, and sideways movements—is fundamental for the hand’s complex functions.