Extensor Carpi Ulnaris
Forearm · Upper Limb
The extensor carpi ulnaris is the most medial of the superficial extensors of the forearm. It arises from the lateral epicondyle of the humerus and the posterior border of the ulna and inserts onto the base of the fifth metacarpal. It extends the wrist and adducts it (ulnar deviation), and, working with flexor carpi ulnaris, it produces pure ulnar deviation of the hand. It is supplied by the posterior interosseous nerve (C7, C8).
Origin, Insertion, Action & Nerve
Origin
Lateral epicondyle of humerus and posterior border of ulna
Insertion
Base of 5th metacarpal
Action
Extension and adduction (ulnar deviation) of wrist
Nerve
Posterior interosseous nerve (C7, C8), Radial
Attachments explained
The Extensor Carpi Ulnaris 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
Lateral epicondyle of humerus and posterior border of ulna
Insertion
Base of 5th metacarpal
Action & function
When the Extensor Carpi Ulnaris contracts, it produces the following movement: Extension and adduction (ulnar deviation) of wrist.
As part of the Forearm 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 Extensor Carpi Ulnaris receives its nerve supply from the Posterior interosseous nerve (C7, C8), Radial. This nerve carries fibres from spinal segment(s) C7, C8.
Because a muscle can only contract when its nerve is intact, injury to the Posterior interosseous nerve or to its spinal roots (C7, C8) can weaken or paralyse the Extensor Carpi Ulnaris, impairing the movements it normally produces (extension and adduction (ulnar deviation) of wrist). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Extensor Carpi Ulnaris (the OIANS method)
Decode the name once more: it extends the wrist and, being ulnaris, deviates the hand toward the little-finger side. Its insertion on the base of the fifth metacarpal places its pull firmly on the medial edge of the wrist.
A powerful way to learn wrist movements is to pair the deviators: extensor carpi ulnaris works with flexor carpi ulnaris to produce pure ulnar deviation, cancelling each other's flexion and extension. That teamwork, plus its posterior interosseous nerve supply, fixes the muscle in the extensor group.
Frequently asked questions
Where is the Extensor Carpi Ulnaris located?
The Extensor Carpi Ulnaris is a muscle of the Forearm group, located in the Upper Limb.
What is the origin of the Extensor Carpi Ulnaris?
Lateral epicondyle of humerus and posterior border of ulna
What is the insertion of the Extensor Carpi Ulnaris?
Base of 5th metacarpal
What movements does the Extensor Carpi Ulnaris produce?
Extension and adduction (ulnar deviation) of wrist
What nerve supplies the Extensor Carpi Ulnaris?
Posterior interosseous nerve (C7, C8), Radial
Is the Extensor Carpi Ulnaris free to study in OIANS?
Yes. The Extensor Carpi Ulnaris 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 Extensor Carpi Ulnaris
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