How many metacarpals are in the hand

Carpal Bones

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

Table of Contents Show

Carpal Bones
Clinical Relevance: Scaphoid Fracture
Metacarpal Bones
Clinical Relevance: Fractures of the Metacarpals
How many metacarpals are in both hands?
What are the 5 metacarpal bones?
How many metacarpal are there?
What are the metacarpals in the hand?

Proximal Row (lateral to medial)	Distal Row (lateral to medial)
Scaphoid Lunate Triquetrum Pisiform (a sesamoid bone, formed within the tendon of the flexor carpi ulnaris)	Trapezium Trapezoid Capitate Hamate (has a projection on its palmar surface, known as the ‘hook of hamate’

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.

Fig 2 – Palmar view of the carpal bones of the left hand.

Fig 3 – Transverse section of the carpal tunnel.

Clinical Relevance: Scaphoid Fracture

The scaphoid bone of the hand is the most commonly fractured carpal bone – typically by falling on an outstretched hand (FOOSH).

In a fracture of the scaphoid, 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.

By Gilo1969 (Own work) [CC-BY-SA-3.0], via Wikimedia Commons

Fig 4 – Radiograph of a scaphoid fracture.

Adapted from work by Iiibalesiii [CC BY-SA 4.0]

Fig 5 – The blood supply to the scaphoid bone runs from distal to proximal.

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 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.

Fig 6 – Bennett’s fracture.

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.

How many metacarpals are in both hands?

The human hand has 27 bones: the carpals or wrist accounts for 8; the metacarpals or palm contains five; the remaining fourteen are digital bones; fingers and thumb. The palm has five bones known as metacarpal bones, one to each of the 5 digits.

What are the 5 metacarpal bones?

Each metacarpal bone has a base, shaft and head..

The first metacarpal articulates with the trapezium..

The second metacarpal articulates with the trapezium, trapezoid and capitate..

The third articulates with the capitate..

The fourth and fifth articulate with the hamate..

How many metacarpal are there?

In humans the five metacarpals are flat at the back of the hand and bowed on the palmar side; they form a longitudinal arch that accommodates the muscles, tendons, and nerves of the palm. The metacarpals also form a transverse arch that allows the fingertips and thumb to be brought together for manipulation.

What are the metacarpals in the hand?

In human anatomy, the metacarpal bones or metacarpus form the intermediate part of the skeletal hand located between the phalanges of the fingers and the carpal bones of the wrist, which forms the connection to the forearm. The metacarpal bones are analogous to the metatarsal bones in the foot.