Second Lumbrical (Hand)
Hand · Upper Limb
The second lumbrical is a slender muscle arising, like the first, from the radial side of a single flexor digitorum profundus tendon, here the tendon to the middle finger, and inserting onto the radial side of that finger's extensor expansion. It flexes the metacarpophalangeal joint and extends the interphalangeal joints of the middle finger, contributing to precise, coordinated finger movement. As one of the two radial (lateral) lumbricals it is supplied by the median nerve (C8, T1).
Origin, Insertion, Action & Nerve
Origin
Radial side of the FDP tendon to the middle finger (unipennate)
Insertion
Radial side of the extensor expansion of the middle finger
Action
Flexes the MCP joint and extends the IP joints of the middle finger
Nerve
Median nerve (C8, T1)
Attachments explained
The Second Lumbrical (Hand) is defined first by where it attaches. Its origin is the more fixed anchor, usually the proximal or more stable end that stays put during contraction, while its insertion is the more mobile point that is pulled toward the origin when the muscle shortens.
Origin
Radial side of the FDP tendon to the middle finger (unipennate)
Insertion
Radial side of the extensor expansion of the middle finger
Action & function
When the Second Lumbrical (Hand) contracts, it produces the following movement: Flexes the MCP joint and extends the IP joints of the middle finger.
As part of the Hand group of the Upper Limb, it works alongside neighbouring muscles to generate smooth, coordinated movement and to stabilise the structures it acts on.
Nerve supply & clinical relevance
The Second Lumbrical (Hand) receives its nerve supply from the Median nerve (C8, T1). This nerve carries fibres from spinal segment(s) C8, T1.
Because a muscle can only contract when its nerve is intact, injury to the Median nerve or to its spinal roots (C8, T1) can weaken or paralyse the Second Lumbrical (Hand), impairing the movements it normally produces (flexes the MCP joint and extends the IP joints of the middle finger). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Second Lumbrical (Hand) (the OIANS method)
Treat the second lumbrical as the middle-finger version of the first: same tendon-to-expansion bridge, same knuckle-flexing and finger-straightening action, just one digit over. Because it too is unipennate, arising from a single profundus tendon, it belongs with the first in the lateral group.
Reinforce the rule of halves rather than learning the nerve afresh: this is the second of the two median-supplied lateral lumbricals. Grouping lumbricals one and two together under the median nerve keeps them distinct from the ulnar-supplied third and fourth.
Frequently asked questions
Where is the Second Lumbrical (Hand) located?
The Second Lumbrical (Hand) is a muscle of the Hand group, located in the Upper Limb.
What is the origin of the Second Lumbrical (Hand)?
Radial side of the FDP tendon to the middle finger (unipennate)
What is the insertion of the Second Lumbrical (Hand)?
Radial side of the extensor expansion of the middle finger
What movements does the Second Lumbrical (Hand) produce?
Flexes the MCP joint and extends the IP joints of the middle finger
What nerve supplies the Second Lumbrical (Hand)?
Median nerve (C8, T1)
Is the Second Lumbrical (Hand) free to study in OIANS?
Yes. The Second Lumbrical (Hand) is free in OIANS: its full origin, insertion, action and nerve details are open to everyone in the Muscle Directory, and because it belongs to the Upper Limb it is also covered by the free Quiz and Flashcard decks. The other regions, the "All Muscles" deck, and the Progress and Explore tools are unlocked with a one-time Lifetime purchase.
Related muscles
Study the Second Lumbrical (Hand)
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