First lumbrical muscle
Musculus lumbricalis primus
- Related terms: Lumbricals (1)
Definition
First lumbrical muscle | |||
Origin | The lateral side of the first flexor digitorum profundus tendon to the index finger | ||
Insertion | Extensor expansions of the 2nd digit (index finger) | ||
Artery | Superficial palmar arch, deep palmar arch, common palmar digital arteries, dorsal digital artery | ||
Innervation | Median nerve (common palmar digital branch) | ||
Action | Flexes the metacarpophalangeal joint and extends the proximal and distal interphalangeal joints of the index finger | ||
The first lumbrical muscle is a slender, unipennate intrinsic muscle of the hand. It originates from the radial side (and adjacent volar surface) of the first flexor digitorum profundus (FDP) tendon, which is destined for the index finger.
The muscle then courses distally, passing around the lateral side of the metacarpophalangeal (MCP) joint of the index finger. It eventually reaches the dorsal aspect of the hand, where it inserts into the dorsal digital expansion (extensor expansion) covering the index finger. This unique insertion mechanism enables the first lumbrical to flex the MCP joint of the index finger while simultaneously extending both the proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints of that same finger.
References
Valenzuela M, Launico MV, Varacallo MA. Anatomy, Shoulder and Upper Limb, Hand Lumbrical Muscles. [Updated 2023 Nov 17]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK534876/
