The capitate bone is a small, irregularly shaped bone located within the wrist, or carpus, and plays a primary role in hand and wrist function. It is one of eight carpal bones, which are organized into two rows. The capitate sits in the middle of the row closest to the hand, acting as a central structure. Understanding its structure and function is key to grasping the mechanics of the wrist joint.
Location and Unique Structure
The capitate bone is the largest of the eight carpal bones, located in the center of the wrist’s distal row. Its name comes from the Latin word caput, meaning “head,” reflecting its prominent, rounded proximal end. This “head” fits into a concave space formed by the scaphoid and lunate bones in the proximal row.
The capitate articulates with seven surrounding bones. Proximally, it connects with the scaphoid and lunate bones. Laterally, it meets the trapezoid bone and the hamate bone. Distally, the capitate articulates primarily with the base of the third metacarpal bone, which leads to the middle finger, and also connects with the second and fourth metacarpals.
Essential Role in Wrist Movement
The capitate acts as the central structural pillar of the wrist, which is essential for supporting both stability and movement. Its central positioning allows it to transmit forces effectively from the hand to the forearm during activities like gripping and lifting. The bone’s alignment with the radius and the third metacarpal creates a column that resists compressive forces.
Its articulations facilitate the synchronized movements necessary for full wrist function, including flexion, extension, and deviation. The capitate serves as a biomechanical anchor around which the other carpal bones rotate. This coordinated motion, particularly at the midcarpal joint, allows for the precise range of motion in the hand. Stability is maintained by the capitate’s extensive ligamentous attachments and its interlocked position within the carpus.
Common Injuries
Although the capitate is generally protected by its central position, it can be involved in trauma, typically from high-energy impacts. Isolated fractures are relatively infrequent, often resulting from a fall onto an outstretched hand with the wrist forced into extreme extension. These fractures can be difficult to diagnose due to the bone’s location and the potential for concurrent injuries.
The capitate is more commonly involved in complex carpal instability patterns, particularly perilunate dislocations. This severe injury occurs when the ligaments surrounding the lunate bone tear, causing the capitate and the rest of the carpus to dislocate. In this dislocation, the lunate bone often remains aligned with the forearm, while the capitate bone is displaced away from it. The capitate serves as a central marker for diagnosis, as its misalignment relative to the lunate signals a major disruption to the wrist’s structural integrity.