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.
|Proximal Row (lateral to medial)||Distal Row (lateral to medial)|
Collectively, the carpal bones form an arch in the coronal plane. A membranous band, the flexor retinaculum, spans between the medial and lateral edges of the arch, forming the carpal tunnel.
Proximally, the scaphoid and lunate articulate with the radius to form the wrist joint (also known as the ‘radio-carpal joint’). In the distal row, all of the carpal bones articulate with the metacarpals.
Clinical Relevance: Scaphoid Fracture
The most commonly fractured bone in the hand is the scaphoid. The most common mechanism is falling on an oustretched hand (FOOSH)
In a scaphoid fracture, the characteristic clinical feature is pain and tenderness in the anatomical snuffbox.
The scaphoid is at particular risk of avascular necrosis after fracture because of its so-called ‘retrograde blood supply’ which enters at its distal end. This means that a fracture to the middle (or ‘waist’) of the scaphoid may interrupt the blood supply to the proximal part of the scaphoid bone rendering it avascular.
Patients with a missed scaphoid fracture are likely to develop osteoarthritis of the wrist in later life.
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 interossei 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 anteriorly, producing shortening of the affected finger.
- Bennett’s fracture – A fracture of the 1st metacarpal base, caused by forced hyperabduction of the thumb. This fracture extends into the first carpometacarpal joint leading to instability and subluxation of the joint. As a result, it often needs surgical repair.
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.