First Lumbrical (Hand)

Hand · Upper Limb

First Lumbrical (Hand) belongs to the Hand group of the Upper Limb. Originating at Radial side of the FDP tendon to the index finger (unipennate), it inserts at Radial side of the extensor expansion of the index finger. Functionally, it flexes the MCP joint and extends the IP joints of the index finger. It is innervated by the Median nerve (C8, T1).

Origin, Insertion, Action & Nerve

Origin

Radial side of the FDP tendon to the index finger (unipennate)

Insertion

Radial side of the extensor expansion of the index finger

Action

Flexes the MCP joint and extends the IP joints of the index finger

Nerve

Median nerve (C8, T1)

Attachments explained

The First 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 index finger (unipennate)

Insertion

Radial side of the extensor expansion of the index finger

Action & function

When the First Lumbrical (Hand) contracts, it produces the following movement: Flexes the MCP joint and extends the IP joints of the index 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 First 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 First Lumbrical (Hand), impairing the movements it normally produces (flexes the MCP joint and extends the IP joints of the index finger). This is why knowing the innervation is central to localising nerve lesions in clinical practice.

How to study the First Lumbrical (Hand) (the OIANS method)

OIANS stands for Origin, Insertion, Action and Nerve, the four facts that uniquely define every skeletal muscle. To learn the First Lumbrical (Hand), work through them in order: picture its origin, trace the muscle to its insertion, reason out the action that shortening between those two points must create, then add the nerve that drives it.

Most students remember the First Lumbrical (Hand) fastest by linking its action back to its attachments rather than memorising each fact in isolation. Once the origin and insertion make sense, the action usually follows logically.