Skilled activities performed by our hand includes writing or picking up objects from the table or eating . These functions involve the bending or flexion at metacarpophalangeal joints and straightening or extension of the joints of the digits or fingers.

This important function is due to small worm like muscles in our hand known as Lumbricals.

Our hand has 8 carpals, 5 metacarpals and 14 phalanges.

The joint between metacarpals and phalanges is known as metacarpophalangeal joint.

The joint between proximal and middle phalanx is known as proximal interphalangeal joint.

The joint between middle and distal phalanx is known as distal interphalangeal joint.

Lumbrical muscles cross all the 3 above joints and cause action at these joints.

In an anatomical position, bones are numbered from lateral to medial side. So, thumb has the first metacarpal and little finger has the 5th metacarpal.


They are 4 in number

Shaped like earthworm

Numbered from lateral to medial side

1st and 2nd lumbricals are unipennate and 3rd and 4th lumbricals are bipennate muscles.

They are the link muscles because they connect flexors with extensors of hand.


All the lumbricals take origin from the tendons of FLEXOR DIGITORUM PROFUNDUS ( FDP).

There are 4 tendons of FDP for the medial four fingers.

1st and 2nd lumbricals:

From the lateral sides of tendons of flexor digitorum profundus to the index and middle finger respectively.

They are unipennate muscles because they arise from only 1 side of the tendon.

3rd and 4th lumbricals :

From the adjacent sides of the tendons of middle finger and ring finger and ring finger and little finger respectively.

They are bipennate muscles because they take origin from the adjacent sides of tendons of FDP respectively.


Into the lateral side of the dorsal digital expansion or extensor expansion and through the expansion a slip of attachment extends into the dorsal surface of the middle and distal phalanx.


The 4 tendons of extensor digitorum forms the dorsal digital expansion or extensor expansion.

They form a triangular hood on the dorsal aspect of metacarpophalangeal joints and proximal phalanges of medial 4 fingers. At the distal end of proximal phalanx they divide onto 3 slips. Middle slip will be attached to the base of the middle phalanx and the 2 lateral slips will fuse at the distal end of middle phalanx and will be attached to the distal phalanx.


1st and 2nd lumbricals are supplied by median nerve

3rd and 4th lumbricals are supplied by ulnar nerve


Injury or paralysis of lumbricals results in CLAW HAND.

Patient will present with extension at metacarpophalangeal joints and flexion at inter phalangeal joints.