Logan Steele
The supinator muscle is a broad muscle in the posterior compartment of the forearm, responsible for rotating the radius laterally, resulting in a movement known as forearm supination. It is located deep within the forearm, wrapping around the proximal third of the radius and connecting it with the ulna. This muscle works in conjunction with the biceps to produce supination, with the notable exception of when the elbow joint is fully extended. The supinator muscle is innervated by the posterior interosseous nerve, a branch of the radial nerve, and is supplied by both the radial and ulnar arteries.
| Characteristics | Values |
|---|---|
| Location | Posterior compartment of the forearm |
| Shape | Spiral |
| Function | Supination of the forearm |
| Attachments | Originates from the lateral epicondyle of the humerus and the posterior surface of the ulna |
| Insertion | Inserts onto the posterior surface of the radius |
| Innervation | Radial nerve (deep branch), posterior interosseous nerve |
| Blood Supply | Superficial layer: Radial artery; Deep layer: Ulnar artery |
| Antagonist | Pronator quadratus muscle |
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What You'll Learn
The supinator muscle is located in the posterior forearm
The supinator muscle consists of two layers: the superficial layer and the deep layer. These layers differ in their mode of attachment. The superficial layer arises from tendinous fibres, surrounding the upper part of the radius and inserting into the lateral edge of the radial tuberosity. On the other hand, the deep layer originates with already formed muscular slips, forming a sling-like structure that encircles the neck of the radius and attaches to its medial surface.
The deep branch of the radial nerve passes between these two layers, providing innervation to the supinator muscle. This nerve becomes the posterior interosseous nerve upon exiting the muscle. Additionally, the supinator muscle receives blood supply from two different sources. The superficial layer is supplied by the radial artery, while the deep layer is supplied by the ulnar artery through its posterior interosseous and posterior interosseous recurrent arteries.
The supinator muscle plays a crucial role in forearm supination, especially during slow and unopposed movements, where it can act as the prime mover. During quick, strong, or forceful supination movements, the supinator muscle is assisted by the biceps brachii muscle. The supinator muscle also works in conjunction with the brachialis muscle to form the floor of the cubital fossa, contributing to the structural stability of the forearm.
Overall, the supinator muscle's location in the posterior forearm and its anatomical characteristics enable it to facilitate forearm supination and contribute to the complex mechanics of the human forearm and hand.
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It rotates the radius laterally
The supinator muscle is a broad muscle in the posterior compartment of the forearm. It is a spiral muscle that wraps around the proximal third of the radius, connecting it with the ulna. This unique anatomy enables the supinator muscle to rotate the radius laterally, producing forearm supination. This movement brings the radius parallel to the ulna, resulting in the hand being in a supine position, with the palm facing up.
The supinator muscle consists of two layers of fibres, or heads, which differ in their mode of attachment. The superficial layer arises from tendinous fibres, while the deep layer originates from already formed muscular slips. These layers surround the upper part of the radius and insert into its lateral edge. The deep branch of the radial nerve passes between these two layers, providing innervation to the supinator muscle.
The supinator muscle is responsible for rotating the radius laterally at the proximal radioulnar joint. This rotation moves the radius into a position parallel to the ulna, allowing the hand to be in a supine position. This action is known as forearm supination, and it is the opposite of pronation, which is produced by the pronator quadratus muscle that rotates the radius medially.
The supinator muscle is essential for simple movements such as rotating the hand to grab something from a bowl. During slow and unopposed supination movements, the supinator muscle is the prime mover. However, for quick, strong, or forceful supination, the supinator muscle is assisted by the biceps brachii muscle. The biceps brachii cannot act as a supinator when the forearm is fully extended, so the most powerful supination occurs when the elbow joint is flexed at a 90-degree angle, such as when turning a screwdriver.
The supinator muscle plays a crucial role in rotating the radius laterally, enabling forearm supination and allowing the hand to be in a supine position. This muscle works in conjunction with the biceps brachii to produce different levels of supination strength, depending on the resistance and elbow joint position.
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It is innervated by the posterior interosseous nerve
The supinator muscle is a broad muscle in the posterior compartment of the forearm. It is responsible for supinating the forearm, which is the action of rotating the radius laterally, resulting in the hand being in a supine position (facing anteriorly, palm up). This movement can be observed when grabbing popcorn from a bowl.
The supinator muscle is innervated by the posterior interosseous nerve, which is a continuation of the deep branch of the radial nerve. This nerve is formed when the radial nerve bifurcates into the posterior interosseous nerve and the superficial radial nerve, just proximal to the supinator muscle. The deep branch of the radial nerve then passes between the two heads of the supinator muscle and exits the muscle, becoming the posterior interosseous nerve.
The nerve roots of the posterior interosseous nerve are primarily from C6, with some C5 involvement, and possible additional C7 innervation. The nerve carries fibres from the C7 and C8 spinal nerves, supplying the majority of the muscles in the posterior compartment of the forearm. The posterior interosseous nerve provides motor innervation to all the muscles in the posterior compartment of the forearm, except for the anconeus muscle, brachioradialis muscle, and extensor carpi radialis longus muscle.
The posterior interosseous nerve is susceptible to entrapment, particularly at the arcade of Frohse, which is part of the supinator muscle. This nerve can be injured in a Monteggia fracture due to the dislocation of the proximal head of the radius bone, resulting in posterior interosseous nerve palsy.
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Supination strength decreases by 64% if the supinator is disabled
The supinator is a broad muscle in the posterior compartment of the forearm, curved around the upper third of the radius. Its function is to supinate the forearm, rotating the radius laterally at the proximal radioulnar joint. This action puts the radius parallel to the ulna, bringing the hand into the supine position (facing anteriorly, palm up).
The supinator consists of two planes of fibres, or superficial and deep layers, between which passes the deep branch of the radial nerve. The deep branch then becomes the posterior interosseous nerve upon exiting the supinator muscle. Its nerve roots are primarily from C6, with some C5 involvement and possible additional C7 innervation. The superficial layer receives blood from the radial artery, while the deep layer is supplied by the ulnar artery.
The supinator always acts together with the biceps, except when the elbow joint is extended. It is the most active muscle in forearm supination during unresisted supination, while the biceps become increasingly active with heavy loading. If the supinator is disabled, such as by injury, supination strength decreases by 64%. This is because the supinator is the prime mover during slow and unopposed supination movements, and even during quick and forceful supination movements, the supinator is assisted by the biceps brachii muscle.
Supinator entrapment syndrome is a nerve syndrome that can result from compression by various soft-tissue masses surrounding the nerve or stress caused by repetitive supination and pronation. This can lead to selective paralysis of the muscles served by the deep radial nerve, such as the extensor muscles and the abductor pollicis longus.
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It is associated with supinator entrapment syndrome
The supinator muscle is a broad muscle in the posterior compartment of the forearm. It wraps around the upper third of the radius, connecting it with the ulna. This muscle is responsible for rotating the radius laterally, resulting in a movement called forearm supination. Its antagonist is the pronator quadratus muscle, which produces the opposite movement of pronation.
The supinator muscle is associated with supinator entrapment syndrome, also known as posterior interosseous nerve syndrome. This syndrome occurs when there is compression of the deep branch of the radial nerve distal to the elbow joint. The radial nerve divides into deep and superficial branches just proximal to the supinator muscle, and this arrangement can lead to entrapment and compression of the deep part. As a result, there may be selective paralysis of the muscles served by this nerve, including the extensor muscles and the abductor pollicis longus.
Supinator entrapment syndrome can be caused by various factors, including compression by soft tissue masses surrounding the nerve and stress from repetitive supination and pronation movements. The deep radial nerve passes through the belly of the supinator in the majority of cases, making it susceptible to nerve entrapment. Symptoms of this syndrome include vague proximal posterior forearm pain in mild cases, while more severe cases may present with weakness in the wrist and finger extensors.
Diagnosis of supinator entrapment syndrome involves careful clinical and electrophysiological examination. Imaging techniques such as sonography and MR imaging can also be used to localize and characterize abnormalities associated with the syndrome. Treatment options include conservative approaches, and if unsuccessful, surgical treatment may be indicated. Surgical exploration of the posterior interosseous nerve can be performed through dorsal or anterior approaches, releasing all potential sites of entrapment.
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Frequently asked questions
The supinator muscle is located in the deep layer of the posterior compartment of the forearm.
The supinator muscle rotates the radius laterally at the proximal radioulnar joint, bringing the hand into the supine position.
The supinator muscle is a supinator of the forearm, meaning it brings the hand into the supinated position.
