Lumbrical muscles of the hand

The lumbrical muscles of the hand are intrinsic muscles of the hand assocated with the FDP tendon.

Summary

• origin: tendons of flexor digitorum profundus in the palm
• insertion: extensor expansion on the dorsum of proximal phalanx after passing along the lateral side of metacarpophalangeal joints
• innervation: following the parent tendon, i.e. ulnar two lumbricals by ulnar nerve (C8, T1), radial two lumbricals by median nerve
• action: provide motor and proprioceptive functions, flex metacarpophalangeal joints, when closing fist extend terminal phalanx

Gross anatomy

The four lumbricals arise from the tendons of the flexor digitorum profundus. The first and second lumbricals arise from the radial side of the FDS tendons of the index and middle fingers. The third lumbrical arises from the adjacent tendons of the middle and ring finger while the fourth arises from the adjacent tendons of the ring and little finger.

Each lumbrical travels on the radial side of its corresponding finger and attaches to the lateral edge of the extensor expansion complex on the dorsum of each finger.

Variant anatomy

Variation in the muscles bellies and attachments of the lumbricals are common with any being possibly unipennate or bipennate. Accessory lumbrical slips have been described as also attaching to the tendons of the flexor digitorum superficialis.

History and etymology

The name comes from the latin 'lumbricus' meaning 'worm' describing the gross appearance of the muscle.