Upper limb
Scaphoid bone
Os scaphoideum
- Origin
- Largest bone of the proximal row, on the thumb side. It bridges both rows: proximally it meets the radius, distally the trapezium and trapezoid, on the ulnar side the lunate and the capitate.
- Insertion
- Attachment for the scapholunate ligament, the radioscaphocapitate ligament and, on its tubercle, the flexor retinaculum.
- Function
- Forms the radial pillar of the wrist and forces the two rows to move together; it tilts palmarly in radial deviation and rights itself in ulnar deviation.
- Innervation
- Anterior and posterior interosseous nerves (articular branches, C6-C8)
- Movement & chain
- It turns with every wrist movement and is the link between the proximal and distal row; losing that link leaves an unstable wrist.
- Palpation
- From the back in the anatomical snuffbox, from the palm as the tubercle at the thumb side of the wrist crease.
- Clinical
- The most commonly fractured carpal bone. Its blood supply runs from distal to proximal, so a fracture through the waist can leave the proximal pole without supply: delayed union, non-union and avascular necrosis. A normal radiograph does not rule out a fracture in the first two weeks.
- Segmental innervation
- C6-C8
- In clinical practice
- With snuffbox tenderness after a fall on the outstretched hand, immobilise and reassess even if the radiograph is clear.
- Region in the model
- Upper limb