Fourth lumbrical muscle
Musculus lumbricalis quartus
- Related terms: Lumbricals (4)
Definition
Fourth lumbrical muscle | |||
Origin | From the medial side of the flexor digitorum profundus tendon to the fourth digit (ring finger) and the lateral side of the flexor digitorum profundus tendon to the fifth digit (little finger) | ||
Insertion | Extensor expansions of the 5th digit (little finger) | ||
Artery | Superficial palmar arch, deep palmar arch, common palmar digital arteries, dorsal digital artery | ||
Innervation | Deep branch of the ulnar nerve | ||
Action | Flexes the metacarpophalangeal joint and extends the proximal and distal interphalangeal joints of the little finger | ||
The fourth lumbrical muscle is a bipennate intrinsic muscle of the hand. It originates from the adjacent sides of the third and fourth flexor digitorum profundus (FDP) tendons. Specifically, its origin includes the ulnar side (and adjacent volar surface) of the FDP tendon going to the ring finger, and the radial side (and adjacent volar surface) of the FDP tendon going to the little finger.
The muscle then courses distally, passing around the lateral side of the metacarpophalangeal (MCP) joint of the little finger. It eventually reaches the dorsal aspect of the hand, where it inserts into the dorsal digital expansion (extensor expansion) covering the little finger. This unique insertion mechanism enables the fourth lumbrical to flex the MCP joint of the little 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/
