Lumbricals of the hand


The lumbricals are intrinsic muscles of the hand that flex the metacarpophalangeal joints and extend the interphalangeal joints.
The lumbrical muscles of the foot also have a similar action, though they are of less clinical concern.

Structure

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 of flexor digitorum profundus and distally to the extensor expansions.
#FormOriginInsertion
FirstunipennateIt originates from the radial side of the most radial tendon of the flexor digitorum profundus.It passes posteriorly along the radial side of the index finger to insert on the extensor expansion near the metacarpophalangeal joint.
SecondunipennateIt originates from the radial side of the second most radial tendon of the flexor digitorum profundus.It passes posteriorly along the radial side of the middle finger and inserts on the extensor expansion near the metacarpophalangeal joint.
ThirdbipennateOne 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.
FourthbipennateOne 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.

Nerve supply

The first and second lumbricals are innervated by the median nerve.
The third and fourth lumbricals are innervated by the ulnar nerve.
This is the usual innervation of the lumbricals. However 1:3 and 3:1 also exist. The lumbrical innervation always follows the innervation pattern of the associated muscle unit of flexor digitorum profundus.

Blood supply

Four separate sources supply blood to these muscles: the superficial palmar arch, the common palmar digital artery, the deep palmar arch, and the dorsal digital artery.

Function

The lumbrical muscles, with the help of the interosseous muscles, simultaneously flex the metacarpophalangeal joints while extending both interphalangeal joints of the digit on which it inserts. The lumbricals are used during an upstroke in writing.

Additional images