Supinator
Forearm · Upper Limb
The supinator is a deep muscle wrapped around the upper part of the radius. It arises from several points, the lateral epicondyle of the humerus, the radial collateral and anular ligaments, and the supinator crest of the ulna, and its fibres curve around to insert on the lateral, posterior, and anterior surfaces of the proximal radius. Its sole action is supination of the forearm, turning the palm upward, a task it performs alone in slow, unresisted movement and with biceps when power is needed. It is supplied by the deep branch of the radial nerve (posterior interosseous nerve, C6, C7), which passes through the muscle and may be compressed there.
Origin, Insertion, Action & Nerve
Origin
Lateral epicondyle of humerus, radial collateral and anular ligaments, supinator crest of ulna
Insertion
Lateral, posterior, and anterior surfaces of proximal radius
Action
Supination of forearm
Nerve
Deep branch of radial nerve (posterior interosseous) (C6, C7)
Attachments explained
The Supinator 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, radial collateral and anular ligaments, supinator crest of ulna
Insertion
Lateral, posterior, and anterior surfaces of proximal radius
Action & function
When the Supinator contracts, it produces the following movement: Supination of forearm.
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 Supinator receives its nerve supply from the Deep branch of radial nerve (posterior interosseous) (C6, C7). This nerve carries fibres from spinal segment(s) C6, C7.
Because a muscle can only contract when its nerve is intact, injury to the Deep branch of radial nerve or to its spinal roots (C6, C7) can weaken or paralyse the Supinator, impairing the movements it normally produces (supination of forearm). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Supinator (the OIANS method)
The name gives the whole action: supinator supinates, turning the palm up. Picture it wrapping around the neck of the radius, so its contraction unrolls the radius outward. Remember the division of labour: the supinator handles slow, unresisted supination, while the biceps is recruited for powerful, resisted supination.
Its clinical hook parallels the pronator teres: the deep branch of the radial nerve (the posterior interosseous nerve) passes through the supinator and can be entrapped there. Linking muscle, nerve, and entrapment site in one image explains why a lesion here causes finger-drop while sparing the wrist extensors above.
Frequently asked questions
Where is the Supinator located?
The Supinator is a muscle of the Forearm group, located in the Upper Limb.
What is the origin of the Supinator?
Lateral epicondyle of humerus, radial collateral and anular ligaments, supinator crest of ulna
What is the insertion of the Supinator?
Lateral, posterior, and anterior surfaces of proximal radius
What movements does the Supinator produce?
Supination of forearm
What nerve supplies the Supinator?
Deep branch of radial nerve (posterior interosseous) (C6, C7)
Is the Supinator free to study in OIANS?
Yes. The Supinator 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 Supinator
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