Phalanges of the hand

At a glance

English

Phalanges of the hand

Latin (TA2)

Ossa digitorum manus

System

Bone

Region

Hand

In order

From the proximal phalanx of first finger of hand to the distal phalanx of fifth finger of hand

About the phalanges of the hand

Each digit of the hand is stiffened by a short chain of bones called phalanges. The thumb has a proximal and a distal phalanx only, while the index, middle, ring and little fingers each have a proximal, a middle and a distal one. The proximal phalanx of every digit meets the head of its metacarpal at the knuckle, or metacarpophalangeal joint, and the bones beyond are linked by interphalangeal joints: a single one in the thumb, and a proximal and a distal one in each finger.

Every phalanx is a miniature long bone with a base, a shaft and a head. The base is the end nearer the palm and carries a concave facet; the head is the end nearer the fingertip. In the proximal and middle phalanges the head is shaped like a small pulley with two condyles and a groove between them, which turns the interphalangeal joints into hinges that allow bending and straightening but almost no sideways movement. The shaft is flattened on its palmar side, where the fibrous sheaths of the flexor tendons attach to its edges, and rounded on the back, which lies under the extensor expansion.

The three rows differ in length and in what attaches to them. Proximal phalanges are the longest and receive the interossei and lumbricals through the extensor expansion. Middle phalanges are shorter; flexor digitorum superficialis divides to insert on the sides of each one, and the central slip of the extensor tendon reaches its base. Distal phalanges are the smallest and end in a flattened, horseshoe-shaped tuft that supports the pulp of the fingertip and the nail bed; flexor digitorum profundus inserts on the palmar side of the base and the terminal extensor tendon on the dorsal side. In the thumb, flexor pollicis longus and extensor pollicis longus take the same places on the distal phalanx.

Fractures of the phalanges are among the commonest broken bones, especially crush injuries of the distal tuft. Two tendon injuries are named after the shape they give the finger: a mallet finger, when the extensor is torn from the distal phalanx so the fingertip droops, and a boutonniere deformity, when the central slip fails over the middle phalanx. Each phalanx ossifies from a centre in the shaft and a single secondary centre at its base.