The capitate bone is the largest of the eight carpal bones that form the wrist. Its name comes from the Latin word “caput,” meaning head, referring to its prominent, rounded shape. Positioned centrally, the capitate is a structural component of the hand’s foundation. It is the first carpal bone to begin ossification, becoming visible on an x-ray when a baby is one to three months old.
Location and Structure
The capitate is centrally located in the distal row of carpal bones, wedged between the trapezoid bone on the thumb side and the hamate bone on the pinky finger side. Proximally, toward the forearm, its rounded head fits into a space formed by the scaphoid and lunate bones. Distally, it primarily connects with the base of the third metacarpal, the long bone of the middle finger.
It also forms smaller articulations with the second and fourth metacarpals. This network of seven articulations makes the capitate a keystone that locks the other carpal bones into a transverse arch. The bone itself has a rounded head, a constricted neck, and a larger body. Its palmar surface has a tubercle that serves as an attachment point for ligaments and muscles.
Role in Wrist Movement
The capitate functions as a stable column for wrist movements and distributes forces from the forearm to the hand. This is important during weight-bearing or gripping, as it transmits stress from the third metacarpal through the wrist.
During wrist flexion and extension—bending the hand down and up—the capitate moves in coordination with the scaphoid and lunate. As the wrist extends, the capitate glides on these two bones. The stability provided by its connections ensures this motion is controlled and smooth.
This bone’s role extends to nearly all wrist motions, including side-to-side movements known as abduction and adduction. By acting as a central pivot, it facilitates movement between the two rows of carpal bones.
Common Injuries and Conditions
Due to its protected position, isolated capitate fractures are uncommon. They result from high-energy trauma, such as a direct blow to the back of the wrist or a fall onto a forcefully bent hand. When a fracture occurs, it is often associated with injuries to adjacent bones, most commonly the scaphoid.
Symptoms of a capitate fracture include deep, localized pain in the center of the wrist, which can be intensified with pressure on the third metacarpal. Swelling on the back of the wrist and a loss of grip strength are also common. The combination of a capitate and scaphoid fracture is a specific injury pattern known as scaphocapitate syndrome.
A primary concern following a capitate fracture is the risk of avascular necrosis. The capitate has a limited blood supply that enters from its distal end and flows proximally toward the head. A fracture across the bone’s neck can disrupt this blood flow, leading to the death of bone tissue and potentially causing chronic pain and arthritis if not properly managed.