The carpal bones are a group of small bones located in the wrist, forming a connection between the forearm and the hand. These bones are compactly arranged, creating the foundation for the wrist joint’s complex movements. Their position allows them to act as a bridge, facilitating the transfer of forces and enabling a wide range of motion.
Anatomy of the Carpal Bones
The wrist contains eight carpal bones, which are organized into two distinct rows: the proximal row and the distal row. The proximal row is positioned closer to the forearm, articulating with the radius bone. This row includes, from the thumb side to the pinky side, the scaphoid, lunate, triquetrum, and pisiform bones. The pisiform is a small, pea-shaped bone that sits on the front surface of the triquetrum.
The distal row of carpal bones lies closer to the hand, connecting with the metacarpal bones that form the palm. From the thumb side, this row consists of the trapezium, trapezoid, capitate, and hamate bones. The capitate is the largest of the carpal bones and occupies a central position in the wrist. These eight bones fit together, forming a semi-rigid structure that is strong and adaptable.
Role of Carpal Bones
The carpal bones work in concert to provide the wrist with mobility and stability. Their intricate arrangement allows for movements such as bending the wrist forward (flexion) and backward (extension). They also enable side-to-side movements, including moving the hand towards the thumb side (radial deviation) and towards the pinky side (ulnar deviation).
These bones also play a role in transmitting forces from the forearm to the hand during activities like gripping or pushing. Their unique shape and ligamentous connections distribute stress across the wrist joint. This arrangement helps to absorb shock and protect the structures within the hand from pressure.
Common Carpal-Related Issues
Due to their central role, carpal bones are susceptible to injuries and conditions. Fractures are common, such as the scaphoid bone, which is the most frequently broken carpal bone and can be challenging to heal due to its limited blood supply. Such fractures often result from falling onto an outstretched hand.
The carpal bones also form the floor and sides of a narrow passageway known as the carpal tunnel. This tunnel houses nerves and tendons that extend into the hand. Compression of the median nerve within this space can lead to carpal tunnel syndrome, characterized by numbness, tingling, and weakness in the hand.