Corpus: Lumbrical muscles of hand

Origin

The lumbrical muscles of hand originate from the tendons of the flexor digitorum profundus muscle. The 1st and 2nd muscles originate from the radial and palmar sides of the tendons of the index and middle fingers. The 3rd muscle originates from the tendons of the middle and ring fingers, and the 4th from the tendons of the ring and little fingers.

Insertion

The short tendons of these muscles extend to the radial side of the corresponding finger and insert at the level of the metacarpophalangeal joints into the dorsal aponeuroses of the 2nd to 5th fingers.

The innervation of the two radial lumbrical muscles (2nd and 3rd fingers) is provided by the median nerve from the brachial plexus (segments: C8 and Th1). The innervation of the two ulnar lumbrical muscles (4th and 5th fingers) is provided by the deep branch of the ulnar nerve (segments: C8 and Th1).

The innervation of the muscles can vary. In about 20 % of cases, there is a different innervation pattern:

• Lumbrical muscle I by the median nerve, lumbrical muscles II - IV by the ulnar nerve, or
• lumbrical muscles I - III by the median nerve, lumbrical muscle IV by the ulnar nerve

The blood supply of the muscles is provided by the following vessels:

• Branches of the superficial palmar arch and the deep palmar arch
• Common palmar digital arteries
• Dorsal digital arteries of hand

The lumbrical muscles of hand cause flexion (bending) at the metacarpophalangeal joints of the fingers and extension (straightening) at the proximal and distal interphalangeal joints.