The second lumbrical is unipennate from the second FDP tendon and is the second median-nerve lumbrical. Together with the first, it maintains the intrinsic-plus position of the index and middle fingers in ulnar nerve palsy. Its anatomical position between the index and middle metacarpals makes it accessible for EMG assessment of median nerve motor function at the hand level.
| Origin | Radial side of the second FDP tendon — unipennate |
|---|---|
| Insertion | Radial side of the extensor expansion of the middle finger |
| Nerve Supply | Median nerve (C8, T1) — most consistently median of the two median lumbricals |
| Blood Supply | Second palmar metacarpal artery |
| Actions | Flexes the MCP joint of the middle finger; Extends the PIP and DIP joints of the middle finger |
|---|
The second lumbrical's median nerve innervation means it is preserved in ulnar nerve palsy but lost in median nerve injuries at the wrist or palm level. Carpal tunnel syndrome may selectively involve the more distal thenar branches while preserving lumbrical function at early stages. EMG of the second lumbrical is a sensitive measure of median nerve motor conduction across the carpal tunnel.
Not palpable directly. Functionally tested by middle finger MCP flexion with IP extension.
Loss of second lumbrical function from selective median nerve injury producing claw posture of the middle finger with ring/little preservation from intact ulnar lumbricals, localising the injury to the median nerve distal to the first lumbrical branch.
