Supinator muscle
Encyclopedia
In human anatomy, 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.
, and "supinator brevis" was used to the muscle now known as the supinator.
lies. The two planes arise in common — the superficial one by tendinous
(the initial portion of the muscle is actually just tendon) and the deeper by muscular fibers — from the supinator crest of ulna
, the lateral epicondyle
of humerus
, the radial collateral ligament
, and the annular radial ligament.
The superficial fibers (pars superficialis) 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, as low down as the insertion of the pronator teres. The upper fibers (pars profunda) of the deeper plane form a sling-like fasciculus
, which encircles the neck of the radius above the tuberosity and is attached to the back part of its medial surface; the greater part of this portion of the muscle is inserted into the dorsal and lateral surfaces of the body of the radius, midway between the oblique line and the head of the bone.
The proximal aspect of the superficial head is known as the arcade of Frohse
or the supinator arch.
, it is able to do this in all positions of elbow flexion and extension.
Supinator always acts together with biceps, except when the elbow joint is extended.
It is the most active muscle in forearm supination during unresisted supination, while biceps becomes increasingly active with heavy loading. Supination strength decreases by 64% if supinator is disabled by, for example, injury.
, a continuation of the deep branch of the radial nerve
.
The radial nerve divides into deep and sensory superficial branches just proximal to the supinator muscle — an arrangement that can lead to entrapment and compression of the deep part, potentially resulting in selective paralysis
of the muscles served by this nerve (the extensor muscles and the abductor pollicis longus
.)
Many possible causes are known for this nerve syndrome, known as supinator entrapment syndrome, including compression by various soft-tissued masses surrounding the nerve, and stress caused by repetitive supination and pronation.
in remaining cases.
Posterior compartment of the forearm
The posterior compartment of the forearm contains the following muscles:-Muscles:* "E/I" refers to "extrinsic" or "intrinsic"....
, curved around the upper third of the radius
Radius (bone)
The radius is one of the two large bones of the forearm, the other being the ulna. It extends from the lateral side of the elbow to the thumb side of the wrist and runs parallel to the ulna, which exceeds it in length and size. It is a long bone, prism-shaped and slightly curved longitudinally...
. Its function is to supinate
Supination
Supination is a position of either the forearm or foot; in the forearm when the palm faces anteriorly, or faces up . Supination in the foot occurs when a person appears "bow-legged" with their weight supported primarily on the anterior of their feet.The hand is supine in the anatomical position...
the forearm.
Terminology
The term "supinator" can also refer more generally to a muscle that causes supination of a part of the body. In older texts, the term "supinator longus" was used to refer to the brachioradialisBrachioradialis
Brachioradialis is a muscle of the forearm that acts to flex the forearm at the elbow. It is also capable of both pronation and supination, depending on the position of the forearm...
, and "supinator brevis" was used to the muscle now known as the supinator.
Origin and insertion
Supinator consists of two planes of fibers, between which the deep branch of the radial nerveDeep branch of the radial nerve
The deep branch of the radial nerve winds to the back of the forearm around the lateral side of the radius between the two planes of fibers of the Supinator, and is prolonged downward between the superficial and deep layers of muscles, to the middle of the forearm.Considerably diminished in size,...
lies. The two planes arise in common — the superficial one by tendinous
Tendon
A tendon is a tough band of fibrous connective tissue that usually connects muscle to bone and is capable of withstanding tension. Tendons are similar to ligaments and fasciae as they are all made of collagen except that ligaments join one bone to another bone, and fasciae connect muscles to other...
(the initial portion of the muscle is actually just tendon) and the deeper by muscular fibers — from the supinator crest of ulna
Ulna
The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form and runs parallel to the radius, which is shorter and smaller. In anatomical position The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form...
, the lateral epicondyle
Lateral epicondyle of the humerus
The lateral epicondyle of the humerus is a small, tuberculated eminence, curved a little forward, and giving attachment to the radial collateral ligament of the elbow-joint, and to a tendon common to the origin of the Supinator and some of the Extensor muscles. In birds, where the arm is somewhat...
of humerus
Humerus
The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....
, the radial collateral ligament
Radial collateral ligament (elbow)
The radial collateral ligament is a short and narrow fibrous band, less distinct than the ulnar collateral, attached, above, to a depression below the lateral epicondyle of the humerus; below, to the annular ligament, some of its most posterior fibers passing over that ligament, to be inserted...
, and the annular radial ligament.
The superficial fibers (pars superficialis) surround the upper part of the radius, and are inserted into the lateral edge of the radial tuberosity
Radial tuberosity
Beneath the neck of the radius, on the medial side, is an eminence, the radial tuberosity; its surface is divided into:* a posterior, rough portion, for the insertion of the tendon of the biceps brachii....
and the oblique line of the radius, as low down as the insertion of the pronator teres. The upper fibers (pars profunda) of the deeper plane form a sling-like fasciculus
Muscle fascicle
In anatomy, a fascicle is a bundle of skeletal muscle fibers surrounded by perimysium, a type of connective tissue.Specialized muscle fibers in the heart that transmit electrical impulses from the Atrioventricular Node to the Purkinje Fibers are fascicles, also referred to as bundle branches...
, which encircles the neck of the radius above the tuberosity and is attached to the back part of its medial surface; the greater part of this portion of the muscle is inserted into the dorsal and lateral surfaces of the body of the radius, midway between the oblique line and the head of the bone.
The proximal aspect of the superficial head is known as the arcade of Frohse
Arcade of Frohse
Arcade of Frohse, sometimes called the supinator arch, is the most superior part of the superficial layer of the supinator muscle, and is a fibrous arch over the posterior interosseous nerve....
or the supinator arch.
Action
Encircling the radius, supinator brings the hand into the supinated position. In contrast to the biceps brachiiBiceps brachii muscle
In human anatomy, the biceps brachii, or simply biceps in common parlance, is, as the name implies, a two-headed muscle located on the upper arm. Both heads arise on the scapula and join to form a single muscle belly which is attached to the upper forearm...
, it is able to do this in all positions of elbow flexion and extension.
Supinator always acts together with biceps, except when the elbow joint is extended.
It is the most active muscle in forearm supination during unresisted supination, while biceps becomes increasingly active with heavy loading. Supination strength decreases by 64% if supinator is disabled by, for example, injury.
Innervation
It is innervated by the posterior interosseous nervePosterior interosseous nerve
The posterior interosseous nerve is a nerve in the forearm. It is the continuation of the deep branch of the radial nerve, after this has crossed the supinator muscle. It is considerably diminished in size compared to the deep branch of the radial nerve...
, a continuation of the deep branch of the radial nerve
Deep branch of the radial nerve
The deep branch of the radial nerve winds to the back of the forearm around the lateral side of the radius between the two planes of fibers of the Supinator, and is prolonged downward between the superficial and deep layers of muscles, to the middle of the forearm.Considerably diminished in size,...
.
The radial nerve divides into deep and sensory superficial branches just proximal to the supinator muscle — an arrangement that can lead to entrapment and compression of the deep part, potentially resulting in selective paralysis
Palsy
In medicine, palsy is the paralysis of a body part, often accompanied by loss of sensation and by uncontrolled body movements, such as shaking. Medical conditions involving palsy include cerebral palsy , brachial palsy , and Bell's palsy ....
of the muscles served by this nerve (the extensor muscles and the abductor pollicis longus
Abductor pollicis longus muscle
The abductor pollicis longus muscle is one of the extrinsic muscles of the hand. It lies immediately below the supinator muscle and is sometimes united with it.-Origin and insertion:...
.)
Many possible causes are known for this nerve syndrome, known as supinator entrapment syndrome, including compression by various soft-tissued masses surrounding the nerve, and stress caused by repetitive supination and pronation.
Variation
The deep radial nerve passes through the belly of supinator in 70% of cases and via the arcade of FrohseArcade of Frohse
Arcade of Frohse, sometimes called the supinator arch, is the most superior part of the superficial layer of the supinator muscle, and is a fibrous arch over the posterior interosseous nerve....
in remaining cases.