lumbricalen

Lumbricalen, or lumbrical muscles, are four small intrinsic muscles of the hand. They lie in the palmar aspect and act on the metacarpophalangeal (MCP) and interphalangeal (IP) joints of the fingers, contributing to precise finger movements.

Each lumbrical originates from the tendons of the flexor digitorum profundus (FDP) and inserts into the extensor expansion (extensor hood) on the proximal phalanges. The first and second lumbricals arise from the radial sides of the FDP tendons to the index and middle fingers, while the third and fourth originate from the adjacent sides of the FDP tendons to the ring and little fingers.

Innervation is split: the first and second lumbricals are supplied by the median nerve (via proper palmar digital branches), and the third and fourth lumbricals are innervated by the deep branch of the ulnar nerve. Blood supply comes from branches of the deep and superficial palmar arches, delivered through the surrounding digital arteries.

Functionally, the lumbricalen flex the MCP joints and assist in extending the IP joints. By acting on the extensor expansions, they help convert flexion at the metacarpophalangeal joints into coordinated extension of the proximal and distal IP joints, collaborating with the interossei and FDP during grip and release.

Clinical relevance is mainly neuropathic. Injury or disease affecting the median nerve can impair the first two lumbricals, while ulnar nerve damage can affect the latter two, leading to diminished fine motor control and altered hand function.