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Portrait of Scaphoid

Anatomy · Bones

Scaphoid

The most commonly fractured carpal bone

Wrist · proximal row of carpal bones

The scaphoid is the boat-shaped carpal bone on the thumb side of the wrist, the largest of the proximal row. It sits in the floor of the anatomical snuffbox and bridges the proximal and distal rows of wrist bones. It is the most commonly fractured carpal bone, and because its blood supply enters from the far end and runs backwards, a fracture across its waist can leave the near fragment without blood and cause it to die.

How to spot them

  • ▸Boat-shaped (Greek skaphe, a boat): the most lateral, thumb-side bone of the proximal row of carpal bones, next to the lunate
  • ▸Articulates with the radius above, the trapezium and trapezoid below, and the lunate and capitate on its inner side
  • ▸A palpable tubercle on its palm side at the base of the thumb; its back forms the floor of the anatomical snuffbox
  • ▸Spans both carpal rows, so it acts as a mechanical link between them

What to know

The boat-shaped wrist bone on the thumb side of the proximal row, whose body forms the floor of the anatomical snuffbox

Scaphoid — the carpal bone in the floor of the anatomical snuffbox.

The single wrist bone most commonly broken, typically in a fall on an outstretched hand with the wrist bent back

Scaphoid — the most commonly fractured carpal bone.

Its blood supply enters at the far end and runs backwards to the near end, so a break across its waist can leave one fragment to die

Scaphoid — retrograde blood supply and avascular necrosis of the proximal pole.

Tenderness in the anatomical snuffbox after a wrist injury, even with a normal first X-ray, is treated as a break of this bone until proved otherwise

Scaphoid — fractures can be invisible on the first film; the wrist is immobilised and re-imaged.

The only wrist bone to span both rows, linking the proximal and distal carpal bones like a bridge

Scaphoid — the 'link' between the two carpal rows.

Fractures of this bone are often fixed with a headless compression screw named for an orthopaedic surgeon called Herbert

Scaphoid — the Herbert screw.

Its Greek name means a boat; a bone of the foot has a Latin name with the same meaning, and this bone was once called by that Latin name too

Scaphoid — formerly os naviculare manus, like the navicular bone of the foot.

Left ununited, a fracture of it leads to a predictable pattern of wrist arthritis, in which the capitate migrates into the gap

Scaphoid — 'SNAC' wrist (scaphoid non-union advanced collapse).

Key ideas

  • Retrograde blood supply: branches of the radial artery enter the bone mainly through its distal half and waist and supply the proximal pole backwards; the more proximal the fracture, the more likely the proximal fragment is deprived of blood, leading to non-union or avascular necrosis.
  • Occult fracture: a scaphoid fracture is often not visible on the first X-ray, so the wrist is splinted and re-examined or imaged again (repeat film or MRI) after about ten to fourteen days.
  • Link function: because it crosses the midcarpal joint, the scaphoid transmits load between the two rows; loss of its integrity or its ligament to the lunate destabilises the whole wrist.

Quick-fire facts

  • •The scaphoid is the largest bone of the proximal row of carpal bones and the most frequently fractured carpal bone (commonly quoted as around 60–70% of carpal fractures).
  • •The typical mechanism is a fall onto the outstretched hand (FOOSH), which hyperextends the wrist; the fracture is most often through the waist.
  • •Its blood supply is retrograde: it enters largely distally, so fractures of the proximal pole are the most prone to non-union and avascular necrosis.
  • •The anatomical snuffbox is bordered by the tendons of extensor pollicis longus (medially) and of abductor pollicis longus and extensor pollicis brevis (laterally); its floor is formed by the scaphoid and trapezium, and the radial artery crosses it.
  • •Its palmar tubercle is palpable at the base of the thumb; the flexor retinaculum and abductor pollicis brevis attach there.
  • •The mnemonic 'So Long To Pinky, Here Comes The Thumb' gives the carpal bones in order, starting with Scaphoid on the thumb side; Kenhub's 'She Likes To Play Try To Catch Her' does the same.
  • •The name 'scaphoid' is from the Greek skaphe, boat; the Latin navicula (little ship) gives the navicular bone of the foot, which is sometimes called the tarsal scaphoid.
  • •A 'SNAC' wrist follows an ununited scaphoid fracture; a 'SLAC' wrist follows rupture of the scapholunate ligament.
  • •The Herbert screw, a headless compression screw introduced in the 1980s, is named for the orthopaedic surgeon Timothy Herbert.

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Sources