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.
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 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.
Oblique head of adductor pollicis (adductor pollicis obliquus)
- dorsal and volar carpometacarpal
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.
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.
- fracture of the capitate and scaphoid
- rotated proximal capitate fracture with articular surface displaced
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.
History and etymology
In Latin, ‘caput’ means ‘head’. Capitate denotes to ‘head shaped’.
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.
CT or MRI imaging will demonstrate the capitate and should be considered if there is clinical suspicion of occult injury.
As with other bones, scintigraphy may demonstrate focal uptake in the setting of fracture.
Upper limb anatomy
skeleton of the upper limb
- carpal bones (mnemonic)
- accessory ossicles of the upper limb
- accessory ossicles of the shoulder
- accessory ossicles of the elbow
- accessory ossicles of the wrist (mnemonic)
- joints of the upper limb
- sternoclavicular joint
- acromioclavicular joint
- glenohumeral joint
- scapulocostal joint (scapulothoracic joint)
- suprahumeral joint
- associated structures
- ossification centres
- elbow joint
- wrist joint
- hand joints
- shoulder joint
- spaces of the upper limb
- pectoral region
- rotator cuff interval
- quadrangular space
- lateral triangular space
- medial triangular space
- cubital tunnel
- cubital fossa
- anatomical snuff box
- carpal tunnel
- Guyon's canal
- space of Poirier
- extensor compartments of the wrist
- muscles of the upper limb
- shoulder girdle
- anterior compartment of the arm
- posterior compartment of the arm
- anterior compartment of the forearm
- posterior compartment of the forearm (extensors)
- thenar (lateral)
- hypothenar (medial)
- accessory muscles
- blood supply to the upper limb
subclavian artery (mnemonic)
- posterior humeral circumflex artery
- anterior humeral circumflex artery
- subscapular artery
- lateral thoracic artery
- thoracoacromial artery
brachial artery (proximal portion)
- deep brachial artery
- superior ulnar collateral
- inferior ulnar collateral
- common interosseous artery
- posterior ulnar recurrent artery
- anterior ulnar recurrent artery
- princeps pollicis artery
- proper dorsal digital artery
- deep palmar brach of the ulnar artery
- persistent median artery of the forearm
- radial artery
- axillary artery
- subclavian artery (mnemonic)
- innervation of the upper limb
- intercostobrachial nerve
brachial plexus (mnemonic)
- branches from the roots
- branches from the trunks
- branches from the cords
- terminal branches
- lymphatic drainage of the upper limb
- 1. Doyle J, Botte M. Surgical Anatomy of the Hand and Upper Extremity. Lippincott Williams & Wilkins. 2003: 57-59. https://books.google.com.au/books?id=96jG5n-vmPcC&lpg=PA57&vq=capitate&pg=PA59#v=onepage&q=capitate&f=false
- 2. Standring S, Borley N, Collins P et al. Gray's Anatomy Fortieth Edition. Churchill Livingstone. 2008.
- 3. Theumann N, Pfirrmann C, Antonio G et al. Extrinsic Carpal Ligaments: Normal MR Arthrographic Appearance in Cadavers. Radiology. 2002: V226, N1: 171-179. http://www.ncbi.nlm.nih.gov/pubmed/12511687