Capitate
Os Capitatum
location_on Center of the distal carpal row, the largest carpal bone
The capitate is the largest carpal bone and occupies the central position in the carpus, articulating with seven bones (more than any other carpal bone). Its rounded head fits into the concavity formed by the scaphoid and lunate, making it the keystone of the distal carpal row. The capitate transmits the majority of the axial load from the hand through the wrist.
Key Anatomical Features
- Largest carpal bone, centrally positioned in the carpus
- Rounded head (capitulum) articulates with the concavity of the lunate
- Articulates with seven bones: scaphoid, lunate, trapezoid, hamate, and metacarpals 2-4
- Narrow neck is susceptible to fracture and avascular necrosis
- Broad distal surface articulates primarily with the third metacarpal
Muscle Attachments
| Muscle | Attachment | Action |
|---|---|---|
| Adductor pollicis (oblique head) | Palmar surface of capitate | Adducts the thumb |
| Flexor pollicis brevis (deep head, variable) | Palmar surface of capitate | Flexes the thumb |
| Intercarpal ligaments | Multiple dorsal and palmar ligaments | Stabilize the capitate within the carpal architecture |
| No major direct muscular attachments | Primarily ligamentous connections | Transmits load from hand to forearm |
Joints and Articulations
| Joint | Type | Connects to |
|---|---|---|
| Lunocapitate joint | Synovial plane | Lunate |
| Third carpometacarpal joint | Synovial plane | Third metacarpal |
| Capitohamate joint | Synovial plane | Hamate |
Common Pathologies
Capitate fracture
Uncommon, accounting for about 1% of carpal fractures. Usually fractures through the waist or neck and is often associated with scaphoid fracture (scaphocapitate syndrome).
Capitate avascular necrosis
Rare condition similar to scaphoid AVN, resulting from the retrograde blood supply to the proximal pole being disrupted by a neck fracture.
Scaphocapitate syndrome
Combined fracture of the scaphoid waist and capitate neck with rotation of the proximal capitate fragment. A rare but classic injury pattern.
Clinical Relevance
The capitate is the first carpal bone to ossify and bears the greatest axial load in the wrist. On a lateral radiograph, the radius, lunate, and capitate should be collinear; disruption of this alignment indicates carpal instability. Scaphocapitate syndrome is easily missed because the capitate fracture may be non-displaced on initial radiographs.
Development and Ossification
The capitate is the first carpal bone to ossify, with its center appearing between ages 1 and 3 months. It is the largest carpal bone from the earliest stage of ossification.
Did You Know?
- Capitate means head-shaped in Latin (caput = head), referring to its rounded proximal surface
- The capitate is both the largest and the first to ossify among the carpal bones
- The capitate articulates with more bones (seven) than any other carpal bone
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