Capitate

The capitate (or os magnum) is the largest of the carpal bones and sits at the centre of the distal carpal row.  A distinctive head shaped bone, it has a protected position in the carpus.

Osteology

The capitate sits in a proximo-distal direction with a waist that is proximal to the transverse midline. The capitate head sits in the space allowed by the lunate and scaphoid bones of the proximal carpal bone row. Proximally, the capitate has rounded surface whilst the distal end has a triangular shape with a palmarly directed apex. The palmar surface is slightly convex with the other surfaces concave being the dorsal, ulnar and radial surfaces. Both dorsal and palmar surfaces are rough to allow for carpal ligament attachment. 

Articulations

Articulations with the capitate include; the scaphoid, lunate, trapezoid, hamate, the base of the third metacarpal and smaller articulations of the second and fourth metacarpal bases.  

  • proximal surface: scaphoid and lunate
  • distal surface: base of third metacarpal and smaller articulations with base of second and fourth metacarpal bones
  • lateral surface: trapezoid
  • medial surface: hamate

There is potential for articulation of the capitate with the triquetrum at the proximal medial border with radial deviation of the wrist. 

Attachments
Musculotendinous

Oblique head of adductor pollicis (adductor pollicis obliquus)

Ligamentous
  • radioscaphocapitate
  • scaphocapitate
  • triquetrocapitate
  • trapeziocapitate
  • capitohamate
  • dorsal and volar carpometacarpal
  • ulnocapitate
Relations

See “Articulations” above.

The dorsal intercarpal and dorsal basal metacarpal arches provide the majority vascular supply. Anastomoses of the ulnar recurrent and palmar intercarpal arches provide additional vascularity.  Vessels enter via both the dorsal and palmar bone surfaces whilst there can be anastomoses between the dorsal and palmar blood supplies.    

On the dorsal surface, vessels enter distal two thirds of dorsal surface with a proximal and palmar direction.  A retrograde course supplies the body and head. Dorsal supply continues through to the palmar surface with terminal vessels to the proximal palmar head.

On the palmar surface, vessels enter distal surface and in a retrograde pattern return proximally. 

The capitate usually has a small facet with the base of the fourth metacarpal, which is absent in approximately 14% of wrists.

Accessory bones from residual secondary ossification centres may be mistaken as fractures. Accessory bones may also be the result of trauma or synovial tag ossification. See: Accessory ossicles of the wrist.

Plain radiograph

Due to its protected position, fractures of the capitate rarely occur.  Fractures may be isolated, but are often associated with perilunate injuries and carpometacarpal fracture dislocation. Fractures may be non-displaced or may demonstrate rotation of the proximal fragment. Proximal pole osteonecrosis may develop.      

Naviculocapitate syndrome:

  • fracture of the capitate and scaphoid
  • rotated proximal capitate fracture with articular surface displaced

Ossification

The capitate has one ossification centre and is generally the first of the carpal bones to ossify. Ossification usually commences in the second month (however can begin at birth). Accessory bones may be associated if there is a failure of fusion from additional ossification centres.

In Latin, ‘caput’ means ‘head’. Capitate denotes to ‘head shaped’. 

Plain radiograph

The capitate may be visualised on a number of series of the distal upper limb including:

Capitate injury can be difficult to see on plain film due to projectional overlapping of bones. 

Cross-sectional imaging

CT or MRI imaging will demonstrate the capitate and should be considered if there is clinical suspicion of occult injury. 

Nuclear medicine

As with other bones, scintigraphy may demonstrate focal uptake in the setting of fracture. 

Upper limb anatomy
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Article information

rID: 41450
Section: Anatomy
Synonyms or Alternate Spellings:
  • os magnum

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    Figure 1: carpal bones
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