Where is the muscle located and how is it structured?
The supinator muscle lies in the deep layer of the posterior forearm. In Latin grammar, its name is derived from the root supinatum (to turn upward/over) with the suffix -or, which denotes the agent performing the action (masculine noun, third declension).
- Origin (O): lateral epicondyle of the humerus (epicondylus lateralis), radial collateral ligament (lig. collaterale radiale), annular ligament of the radius (lig. anulare radii), and the crest of the ulna.
- Insertion (I): proximal (upper) third of the lateral and anterolateral surface of the radius.
Topography and relations to neighboring structures
The supinator plays an important role in the topography of the elbow region:
- Relation to the joint: the muscle directly covers the capsule of the elbow joint externally (laterally), providing protection (whereas the capsule remains unprotected by muscles on the medial side).
What passes through the supinator canal?
The muscle consists of superficial and deep parts, between which the supinator canal (canalis supinatorius) is formed.
At the level of the lateral epicondyle, the radial nerve divides into two branches. Its deep branch (r. profundus n. radialis) runs laterally and enters this canal. Inside the canal, the nerve and the supinator muscle wrap around the neck of the radius, after which the nerve emerges between the muscles of the posterior forearm to innervate them.
Function, blood supply, and innervation
- Function (A): supinates the forearm (rotates it laterally). This action is especially pronounced when the elbow joint is extended. Note: The biceps brachii (*m. biceps brachii*) is also a powerful supinator.
- Blood supply: supplied by branches of the radial recurrent artery (a. recurrens radialis) and the posterior interosseous artery (a. interossea posterior).
- Innervation (N): deep branch of the radial nerve (n. radialis), fibers from spinal segments C6–C7.
Clinical significance
- Mononeuropathies: during a neurological consultation, it is recommended to assess motor function, muscle strength, and trophic status of the supinator. This is evaluated alongside examination of the wrist and finger extensors, brachioradialis, and triceps brachii muscles.
- Extrapyramidal disorders: lesions of the extrapyramidal system (extrapyramidal paralysis) lead to increased muscle tone of a rigid type. A characteristic sign is the uniform increase in tone in both pronators and supinators.
Class and exam questions
Which muscle assists the supinator in rotating the forearm?
The biceps brachii (
How to distinguish the radius from the ulna when studying the attachment sites of the supinator?
When determining the side of forearm bones, it is important to remember that the radius is always positioned laterally and the ulna medially. The supinator originates from the crest of the ulna and inserts onto the lateral surface of the radius.
Which other muscles are innervated by the radial nerve along with the supinator?
The list of muscles associated with the radial nerve includes the triceps brachii, anconeus, brachioradialis, radial extensors of the wrist, extensor digitorum, extensor carpi ulnaris, abductor pollicis longus, extensors of the thumb, and extensor indicis.
What else to study on this topic
- Radial nerve (n. radialis)
- Ulna
- Radius
- Biceps brachii muscle (m. biceps brachii)
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