Dominic Stone
The supinator muscle is a broad muscle in the posterior compartment of the forearm, responsible for supinating the forearm, or twisting it into the palm-up position. This movement is essential for everyday tasks such as turning a screwdriver or a key. The supinator works with the biceps brachii to achieve powerful supination and is innervated by the deep branch of the radial nerve. The supinator is also important as a location where the radial nerve can be entrapped, leading to potential paralysis of the muscles it serves.
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What You'll Learn
- The supinator muscle is located in the posterior compartment of the forearm
- The biceps brachii is the main supinator of the forearm
- The supinator works with the biceps brachii for powerful supination
- The supinator muscle consists of two planes of fibres
- The supinator muscle is innervated by the radial nerve
The supinator muscle is located in the posterior compartment of the forearm
The supinator muscle is responsible for supinating the forearm, which involves twisting the forearm so that the palm faces upwards. This movement is essential for grip, hand movement, and the everyday functioning of the upper limb. The ability to supinate gives us enhanced functionality, allowing us to perform tasks such as turning a screwdriver or a key.
The supinator works in conjunction with the biceps brachii to achieve powerful supination. However, the biceps brachii is unable to supinate when the elbow is extended. The biceps brachii is also prone to injury, particularly in the tendon of the long head and the distal tendon, which inserts into the radius.
The supinator muscle is innervated by the deep branch of the radial nerve, which becomes the posterior interosseous nerve upon exiting the muscle. Its nerve roots are primarily from C6, with some C5 involvement and possible additional innervation from C7. The radial nerve divides into deep and sensory superficial branches just proximal to the supinator muscle, which can lead to entrapment and potential paralysis of the muscles it serves.
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The biceps brachii is the main supinator of the forearm
The biceps brachii is a large muscle that lies on the front of the upper arm between the shoulder and the elbow. It is one of the most variable muscles in the human body and has two or three heads. The biceps brachii is the main supinator of the forearm, i.e., it turns the palm upwards. This action requires the humeroulnar joint of the elbow to be at least partially flexed. If the humeroulnar joint is fully extended, supination is primarily carried out by the supinator muscle.
The biceps brachii is a powerful supinator due to the distal attachment of the muscle at the radial tuberosity, on the opposite side of the bone from the supinator muscle. When flexed, the biceps effectively pulls the radius back into its neutral supinated position in concert with the supinator muscle. The biceps brachii also functions as an important flexor of the forearm, particularly when the forearm is supinated.
The supinator muscle is located in the posterior compartment of the forearm. It is a broad muscle that curves around the upper third of the radius. The supinator consists of two planes of fibres, between which passes the deep branch of the radial nerve. The supinator muscle has a broad origin from the ulna and humerus. The two layers of fibres originate in common from the supinator crest of the ulna, the lateral epicondyle of the humerus, the radial collateral ligament, and the annular radial ligament.
The biceps and supinator muscles work together when powerful supination is required. However, the biceps brachii is unable to supinate when the elbow is extended. The radial nerve divides into deep and sensory superficial branches just proximal to the supinator muscle. This can lead to entrapment and compression of the deep branch and could potentially result in selective paralysis of the muscles served by this nerve.
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The supinator works with the biceps brachii for powerful supination
The supinator is a broad muscle in the posterior compartment of the forearm. It curves around the upper third of the radius and consists of two layers of fibres. The supinator muscle's main function is to supinate the forearm. This can be done with the elbow in any position of flexion or extension.
However, for a quick, strong, forceful supination movement, or when the movement happens against resistance, the supinator muscle is assisted by the biceps brachii muscle. The biceps brachii is a powerful supinator when the limb is pronated. It is unable to supinate when the elbow is extended. The most powerful supination occurs when the elbow joint is flexed to 90 degrees. An example of this movement is turning a screwdriver or uncorking a wine bottle.
The supinator muscle works with the biceps brachii for powerful supination. The biceps brachii is also one of the muscles that flex the elbow, along with the brachialis and brachioradialis. The supination movement occurs at the radioulnar joints. The head of the radius is discoid and fits with the radial neck within the circular anular ligament, attaching the proximal radius to the ulna. The wheel-like rotation of the head of the radius enables supination (palm facing upwards).
The supinator muscle is innervated by the deep branch of the radial nerve, which becomes the posterior interosseous nerve upon exiting the supinator muscle. Its nerve roots are primarily from C6, with some C5 involvement. The supinator muscle is also known as supinator longus in older texts.
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The supinator muscle consists of two planes of fibres
The supinator muscle is a broad muscle located in the posterior compartment of the forearm. It is responsible for supinating the forearm, allowing the hand to be in the supine position (palm facing upwards). This muscle works in synergy with several other muscles to enable a wide range of functional movements, such as turning a screwdriver or opening a bottle of wine.
The supinator muscle consists of two planes or layers of fibres, namely the superficial layer and the deep layer. These layers differ in their mode of attachment. The superficial layer arises from tendons, while the deep layer originates from already formed muscular slips. Despite their distinct origins, both layers share common landmarks for their attachments. These landmarks include several osteofibrous structures of the elbow, such as the lateral epicondyle of the humerus, the radial collateral ligament, the annular radial ligament, the supinator crest of the ulna, and the adjacent part of the ulnar fossa.
The superficial layer of fibres surrounds the upper part of the radius and inserts into the lateral edge of the radial tuberosity and the oblique line of the radius. This layer receives its blood supply from the radial artery, specifically through its radial recurrent branch. On the other hand, the deep layer of fibres forms a sling-like structure that encircles the neck of the radius above the radial tuberosity. This deeper layer is supplied by the ulnar artery, particularly through its posterior interosseous and posterior interosseous recurrent arteries.
Between these two layers of the supinator muscle runs the deep branch of the radial nerve. This nerve divides into deep and sensory superficial branches just proximal to the supinator muscle. This unique arrangement can sometimes lead to entrapment and compression of the deep branch, potentially resulting in selective paralysis of the muscles it serves. This condition is known as supinator entrapment syndrome and can be caused by repetitive supination and pronation movements.
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The supinator muscle is innervated by the radial nerve
The supinator muscle is a spiral muscle in the posterior compartment of the forearm that rotates the radius laterally to accomplish forearm supination. It is innervated by the deep branch of the radial nerve, which passes through the belly of the supinator in 70% of cases. The radial nerve divides into deep and sensory superficial branches just proximal to the supinator muscle. This arrangement can lead to entrapment and compression of the deep branch, potentially resulting in selective paralysis of the muscles served by this nerve. This nerve syndrome is known as supinator entrapment syndrome.
The supinator muscle consists of two planes or layers of fibres, between which passes the deep branch of the radial nerve. The two planes arise in common, with the superficial one originating as tendons and the deeper one by muscular fibres. The superficial fibres surround the upper part of the radius and are inserted into the lateral edge of the radial tuberosity and the oblique line of the radius. The upper fibres of the deeper plane form a sling-like structure that encircles the neck of the radius above the tuberosity and is attached to the back part of its medial surface.
The nerve roots of the radial nerve are primarily from C6, with some C5 involvement. There is also possible additional C7 innervation. The radial nerve innervates the muscles in the posterior compartment of the forearm. Before the radial nerve passes through the supinator, it is commonly identified as the deep branch of the radial nerve. After exiting the supinator muscle, the deep branch of the radial nerve becomes the posterior interosseous nerve.
The supinator muscle is the prime supinator of the forearm and works with the biceps brachii if powerful supination is required. However, the biceps brachii cannot supinate when the elbow is extended. The simple rotation of the hand when grabbing popcorn from a bowl is an example of an unopposed supination movement where the supinator muscle can act alone. More forceful supination movements, such as turning a screwdriver or pulling out a cork from a bottle of wine, require assistance from the biceps brachii.
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Frequently asked questions
Supination is the act of twisting the forearm into the palm-up position.
The supinator muscle is the prime muscle responsible for supinating the forearm. The biceps brachii of the upper arm also supinates the forearm.
The supinator muscle is located in the posterior compartment of the forearm. It curves around the upper third of the radius and consists of two layers of fibres. The supinator muscle provides about half the power of the biceps muscle for supination.
