| Lumbricals of the hand | |
|---|---|
.png) The muscles of the left hand. Palmar surface. (first lumbricalis labeled at bottom right of muscular group) | |
| Details | |
| Origin | Flexor digitorum profundus |
| Insertion | Extensor expansion |
| Artery | Superficial palmar arch,common palmar digital arteries,deep palmar arch,dorsal digital artery |
| Nerve | Third and fourthdeep branch of ulnar nerve, first and secondmedian nerve |
| Actions | Flexmetacarpophalangeal joints,extendinterphalangeal joints |
| Identifiers | |
| Latin | musculi lumbricales manus |
| TA98 | A04.6.02.065 |
| TA2 | 2532 |
| FMA | 37385 |
| Anatomical terms of muscle | |
Thelumbricals are intrinsicmuscles of thehand thatflex themetacarpophalangeal joints,[1] andextend theinterphalangeal joints.[1][2]
Thelumbrical muscles of the foot also have a similar action, though they are of less clinical concern.
The lumbricals are four, small, worm-like muscles on each hand. These muscles are unusual in that they do not attach to bone. Instead, they attach proximally to the tendons offlexor digitorum profundus,[1][2][3] and distally to theextensor expansions.[1][3] The first and second lumbricals areunipennate, while the third and fourth lumbricals arebipennate.[2][4]
| # | Form | Origin | Insertion |
| First | unipennate | It originates from the radial side of the most radial tendon of the flexor digitorum profundus (corresponding to the index finger). | It passes posteriorly along the radial side of the index finger to insert on theextensor expansion near themetacarpophalangeal joint. |
| Second | unipennate | It originates from the radial side of the second most radial tendon of the flexor digitorum profundus (which corresponds to the middle finger). | It passes posteriorly along the radial side of the middle finger and inserts on the extensor expansion near the metacarpophalangeal joint. |
| Third | bipennate | One head originates on the radial side of the flexor digitorum profundus tendon corresponding to the ring finger, while the other originates on the ulnar side of the tendon for the middle finger. | The muscle passes posteriorly along the radial side of the ring finger to insert on its extensor expansion. |
| Fourth | bipennate | One head originates on the radial side of the flexor digitorum profundus tendon corresponding to the little finger, while the other originates on the ulnar side of the tendon for the ring finger. | The muscle passes posteriorly along the radial side of the little finger to insert on its extensor expansion. |
The first and second lumbricals (the most radial two) areinnervated by themedian nerve. The third and fourth lumbricals (most ulnar two) are innervated by the deep branch ofulnar nerve.[5]
This is the usual innervation of the lumbricals (occurring in 60% of individuals). However 1:3 (median:ulnar - 20% of individuals) and 3:1 (median:ulnar - 20% of individuals) also exist. The lumbrical innervation always follows the innervation pattern of the associated muscle unit offlexor digitorum profundus (i.e. if the muscle units supplying thetendon to themiddle finger are innervated by the median nerve, the second lumbrical will also be innervated by the median nerve).[6]
Four separate sources supply blood to these muscles: thesuperficial palmar arch, thecommon palmar digital artery, thedeep palmar arch, and thedorsal digital artery.[7]
The lumbrical muscles, with the help of the interosseous muscles, simultaneously flex themetacarpophalangeal joints while extending bothinterphalangeal joints of the digit on which it inserts. The lumbricals are used during an upstroke in writing.
The term "lumbrical" comes from theLatin, meaning "worm".[8]
