Upper limb
Capitate bone
Os capitatum
- Origin
- Largest carpal bone, in the middle of the hand. Its round head fits the socket formed jointly by the scaphoid and the lunate; distally it mainly carries the base of the third metacarpal.
- Insertion
- Attachment for the radioscaphocapitate, scaphocapitate and capitohamate ligaments and for the oblique head of adductor pollicis.
- Function
- Forms the axis the wrist moves around: all the movement axes of the wrist run roughly through the head of this bone.
- Innervation
- Anterior and posterior interosseous nerves (articular branches, C6-C8)
- Movement & chain
- It moves little relative to the distal row but turns as a whole with the hand; the lunate tilts around it.
- Palpation
- From the back, in the hollow proximal to the base of the third metacarpal, in line with the middle finger.
- Clinical
- In perilunate dislocation the head slips out of the socket of the lunate; this is the core of the so called greater arc of injuries. Like the scaphoid, its proximal pole has a vulnerable blood supply.
- Segmental innervation
- C6-C8
- In clinical practice
- When judging wrist movement this is the reference point: aim the goniometer at the axis through this bone rather than at the forearm.
- Region in the model
- Upper limb