Bones of the Hand: Carpals, Metacarpals and Phalanges

Fig 1.0 - Overview of the bones of the hand.

Fig 1.0 – Overview of the bones of the hand.

The bones of the hand provide support and flexibility to the soft tissues. They can be divided into three categories:

  • Carpal bones (Most proximal) – A set of eight irregularly shaped bones. These are located in the wrist area.
  • Metacarpals – There are five metacarpals, each one related to a digit
  • Phalanges (Most distal) – The bones of the fingers. Each finger has three phalanges, except for the thumb, which has two.

In this article, we shall look at the anatomical features of the bones of the hand.


Carpal Bones

The carpal bones are a group of eight, irregularly shaped bones. They are organised into two rows – proximal and distal.

In the proximal row, the bones are (lateral to medial):

  • Scaphoid
  • Lunate
  • Triquetrum
  • Pisiform – A sesamoid bone, formed within the tendon of the flexor carpi ulnaris

In the distal row, the bones are (lateral to medial):

  • Trapesium
  • Trapezoid
  • Capitate
  • Hamate – has a projection on its palmar surface called the hook of hamate

Proximally, the scaphoid and lunate articulate with the radius to form the wrist joint. In the distal row, all of the carpal bones articulate with the metacarpals.

Fig 1.1 - Palmar view of the carpal bones.

Fig 1.1 – Palmar view of the carpal bones.

Clinical Relevance: Fractures of the Carpal Bones

Fig 1.3 - Radiograph of a scaphoid fracture.

Fig 1.3 – Radiograph of a scaphoid fracture.

The two carpal bones that are most commonly fractured are the scaphoid and lunate. The most common mechanism of injury in both cases is FOOSH (falling on an outstretched hand).

The scaphoid is more commonly fractured. Characteristically there is pain and tenderness in the anatomical snuffbox. A fracture  needs to be fixed quickly, as the off the blood supply to the proximal part of the bone can be cut off, causing it to undergo asvascular necrosis. Patients with an undiagnosed scaphoid fracture are very likely to develop wrist arthritis.

A lunate fracture occurs when falling on a outstretched hand causes hyperextension at the wrist. It is can be associated with some median nerve damage.

Metacarpal Bones

The metacarpal bones articulate proximally with the carpals, and distally with the proximal phalanges. They are numbered, and each associated with a digit:

  • Metacarpal I – Thumb.
  • Metacarpal II – Index finger.
  • Metacarpal III – Middle finger.
  • Metacarpal IV – Ring finger.
  • Metacarpal V – Little finger.

Each metacarpal consists of a base, shaft and a head. The medial and lateral surfaces of the metacarpals are concave, allowing attachment of the interoessei muscles.

Fig 1.2 - Bennett's fracture.

Fig 1.2 – Bennett’s fracture.

Clinical Relevance: Fractures of the Metacarpals

There are two common fractures of the metacarpals.

  • Boxer’s fracture –  A fracture of the 5th metacarpal neck. It is usually caused by a clenched fist striking a hard object.  The distal part of the fracture is displaced posteriorly, producing shortening of the affected finger.
  • Bennett’s fracture – A fracture of the 1st metacarpal base, extending into the carpometacarpal joint. It is caused by hyperabduction of the thumb.

Phalanges

The phalanges are the bones of the fingers. The thumb has a proximal and distal phalanx, while the rest of the digits have proximal, middle and distal phalanges.

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