Bones of the Hand: Carpals, Metacarpals and Phalanges
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.
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):
- Pisiform – A sesamoid bone, formed within the tendon of the flexor carpi ulnaris
In the distal row, the bones are (lateral to medial):
- 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.
Clinical Relevance: Fractures of the Carpal Bones
The two carpal bones that are most commonly fractured are the scaphoid and lunate. The usual mechanism of injury in both cases is FOOSH (falling on an outstretched hand).
In a scaphoid fracture, the classical clinical feature is pain and tenderness in the anatomical snuffbox. This fracture type needs to be reduced quickly, as the blood supply to the proximal part of the bone can be cut off – causing it to undergo avascular necrosis. Patients with a missed scaphoid fracture are likely to develop wrist arthritis in later life.
A lunate fracture occurs when there is hyperextension at the wrist. It is associated with damage to the median nerve.
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.
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.
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.