Lumbrical muscles of hand

At a glance

English

Lumbrical muscles of hand

Latin (TA2)

Musculi lumbricales manus

System

Muscle

Region

Upper limb

Side

Paired, left and right

About the lumbrical muscles of hand

The lumbrical muscles of the hand are four small muscles shaped like worms, numbered from the index side to the little finger side. They are unusual because they arise from tendons rather than bone, and because they link the flexor and extensor systems of the fingers.

Each lumbrical springs from a tendon of flexor digitorum profundus in the palm, just beyond the carpal tunnel. The first and second, for the index and middle fingers, each arise from the radial side of a single tendon. The third and fourth arise from the facing sides of two neighbouring tendons, so they have a double origin. Each muscle passes forward on the radial side of its finger, in front of the deep transverse metacarpal ligament, and its tendon joins the radial edge of the extensor expansion over the proximal phalanx.

Through this attachment the lumbricals bend the knuckle joints while straightening the middle and end joints of the fingers, the position used in holding a book or writing. They also act as sensors, being rich in stretch receptors that help fine finger control. The first two are supplied by the median nerve and the third and fourth by the deep branch of the ulnar nerve. Their blood comes from the superficial and deep palmar arches and from the digital arteries that leave them.

When the ulnar nerve is damaged, the ring and little fingers lose their lumbricals and interossei and curl into a claw, with the knuckles extended and the end joints bent. The index and middle fingers are less affected because their lumbricals keep the median supply. Infection in the palm can spread along the sheaths of the lumbricals into the web spaces.

Attachments, action and supply

Origin

Tendons of flexor digitorum profundus in the palm: the first and second from one tendon each, the third and fourth from two adjacent tendons.

Insertion

Radial side of the extensor expansions of the index, middle, ring and little fingers.

Action

Bend the finger knuckles while straightening the interphalangeal joints.

Nerve supply

First and second by the median nerve; third and fourth by the deep branch of the ulnar nerve (C8, T1).

Blood supply

Superficial and deep palmar arches and their digital branches.