The brachioradialis is a muscle of the forearm that flexes the forearm at the elbow. It is capable of both pronation and supination, depending on the position of the forearm, it is attached to the distal styloid process of the radius by way of the brachioradialis tendon, to the lateral supracondylar ridge of the humerus. The brachioradialis is a superficial, fusiform muscle on the lateral side of the forearm that attaches proximally on the lateral supracondylar ridge of the humerus and distally on the radius, close to its styloid process. Near the elbow, it forms the lateral limit of the cubital elbow pit. Despite the bulk of the muscle body being visible from the anterior aspect of the forearm, the brachioradialis is a posterior compartment muscle and is innervated by the radial nerve. Of the muscles that receive innervation from the radial nerve, it is one of only four that receive input directly from the radial nerve; the other three are the triceps and extensor carpi radialis longus. The brachioradialis flexes the forearm at the elbow.
When the forearm is pronated, the brachioradialis tends to supinate. In a supinated position, it tends to pronate; this assists the biceps brachii. The brachioradialis is a stronger elbow flexor when the forearm is in a midposition between supination and pronation at the radioulnar joint; when pronated, the brachioradialis is more active during elbow flexion since the biceps brachii is in a mechanical disadvantage. With the insertion of the muscle so far from the fulcrum of the elbow, the brachioradialis does not generate as much joint torque as the brachialis or the biceps, it is effective when those muscles have partially flexed at the elbow. The brachioradialis flexes the forearm at the elbow when quick movement is required and when a weight is lifted during slow flexion of the forearm; the muscle is used to stabilize the elbow during rapid flexion and extension while in a midposition, such as in hammering. The brachioradialis is synergistic with the biceps brachii. Illustration: upper-body/brachialis from The Department of Radiology at the University of Washington Anatomy figure: 07:01-09 at Human Anatomy Online, SUNY Downstate Medical Center - "Transverse section through the left arm just proximal to the elbow."
Anatomy figure: 07:03-07 at Human Anatomy Online, SUNY Downstate Medical Center - "Superficial muscles of the anterior compartment of the left forearm." Anatomy figure: 09:02-02 at Human Anatomy Online, SUNY Downstate Medical Center - "Superficial muscles of the posterior compartment of the left forearm." Lesson5musofpostforearm at The Anatomy Lesson by Wesley Norman
Annular ligament of radius
The annular ligament is a strong band of fibers that encircles the head of the radius, retains it in contact with the radial notch of the ulna. Per Terminologia Anatomica, the spelling is "anular", but the spelling "annular" is encountered; the annular ligament is attached by both its ends to the anterior and posterior margins of the radial notch of the ulna, together with which it forms the articular surface that surrounds the head and neck of the radius. The ligament is strong and well defined, yet its flexibility permits the oval head of the radius to rotate during pronation and supination; the head of the radius is wider than the bone's neck, because the annular ligament embraces both, the radial head is "trapped" inside the ligament which thus acts to prevent distal displacement of the radius. Superiorly, the ligament is supported by attachments to the radial collateral ligament and the fibrous capsule of the elbow joint. Inferiorly, a few fibres attached to the neck of the radius support a fold of the synovial membrane without interfering with the movements at the joint.
The fibrocartilage on the upper part of the ligament is continuous with the hyaline cartilage of the radial notch. At the posterior attachment the ligament widens to reach below the radial notch. A thickened band which extends from the inferior border of the annular ligament below the radial notch to the neck of the radius is known as the quadrate ligament. Children who have not finished fusing their proximal radial epiphyseal plate may suffer dislocations of this joint; this happens when parents jerk their children by their arms, e.g. the act of grabbing a child away from traffic. This article incorporates text in the public domain from page 324 of the 20th edition of Gray's Anatomy Anatomy figure: 10:5a-02 at Human Anatomy Online, SUNY Downstate Medical Center
Radial recurrent artery
The radial recurrent artery arises from the radial artery below the elbow. It ascends between the branches of the radial nerve, lying on the supinator muscle and between the brachioradialis muscle and the brachialis muscle, supplying these muscles and the elbow-joint, anastomosing with the terminal part of the profunda brachii; this article incorporates text in the public domain from page 594 of the 20th edition of Gray's Anatomy lesson4arteriesofarm at The Anatomy Lesson by Wesley Norman lesson4artofforearm at The Anatomy Lesson by Wesley Norman
Deep branch of radial nerve
The radial nerve divides into a superficial and deep branch at the cubital fossa. 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, is prolonged downward between the superficial and deep layers of muscles, to the middle of the forearm; the deep branch provides motor function to the muscles in the posterior compartment of the forearm, the extensor muscles of the hand. The radial nerve arises from the posterior cord of the brachial plexus; the posterior cord takes nerves from the upper and middle trunk, so the radial nerve is formed from the anterior rami of C5 through T1. The radial nerve passes through the axilla, it can be compressed against the humerus by crutches. Symptoms of damage to the deep branch of the radial nerve include "wrist drop", the flexion of fingers and wrist, since the extensor muscles supplied by the nerve are paralyzed. Normal sensation of the skin is retained, since this nerve only provides sensory function to ligaments and articulations of the carpal and metacarpal joints.
Since the nerve passes dorsally around the head of the radius, it is susceptible to traction or compression injuries when the elbow joint is injured, in particular, radial dislocation. Another area of potential entrapment is the arcade of Frohse, a fibrous arch formed from the proximal part of the superficial head of the supinator, under which the deep branch of the radial nerve passes; the passage for the nerve varies in size. In some cases of spontaneous paralysis of the nerve, releasing this fibrous band released pressure on the nerve and restored function Considerably diminished in size, it descends as the posterior interosseous nerve. For some authors, the deep branch of the radial nerve is the same as the posterior interosseous nerve; this article incorporates text in the public domain from page 944 of the 20th edition of Gray's Anatomy lesson5nervesofhand at The Anatomy Lesson by Wesley Norman
Pronator quadratus muscle
Pronator quadratus is a square shaped muscle on the distal forearm that acts to pronate the hand. As it is on the anterior side of the arm, it is innervated by a branch of the median nerve, the anterior interosseous nerve. Arterial blood comes via the interosseous artery, its fibres run perpendicular to the direction of the arm, running from the most distal quarter of the anterior ulna to the distal quarter of the radius. It has two heads: the superficial head originates from the anterior distal aspect of the diaphysis of the ulna and inserts into the anterior distal diaphysis of the radius, as well as its anterior metaphysis; the deep head has the same origin. It is the only muscle that attaches only to the radius at the other end; when pronator quadratus contracts, it pulls the lateral side of the radius towards the ulna, thus pronating the hand. Its deep fibers serve to keep the two bones in the forearm bound together. Moreover, this muscle can be absent in some humans, that does not affect the action of pronation notably, as the pronator teres does the major role in that action.
The lateral corticospinal tract is responsible for the motor pathway of the pronator quadratus. This tract begins in the precentral gyrus of the motor cortex where a signal is transmitted from the upper motor nerve through the progression tracts of the internal capsule and through the cerebral peduncles of the midbrain, it decussates in the medulla and travels down the lateral corticospinal tract in the lateral column of the spinal cord. It decussates in the spinal cord and synapses at the anterior horn to the lower motor neurons of the skeletal muscles; the cuneate fasciculus tract is responsible for the sensation of the pronator quadratus position and movement, deep touch, visceral pain, vibration. This tract begins in the dorsal nerve root where the signal is transmitted through the dorsal horn and up the posterior column of the spinal cord, it synapses with an interneuron in the gracile nucleus. It decussates in the medial lemniscus of the medulla, travels through the cuneate nucleus and through the medial lemniscus of the midbrain to synapse in the thalamus.
It synapses with a third order neuron and transmits the signal to the postcentral gyrus of the somesthetic cortex. This could not specific to this muscle. Illustration: upper-body/pronator-quadratus from The Department of Radiology at the University of Washington
Radial collateral ligament of elbow joint
The radial collateral ligament, lateral collateral ligament, or external lateral ligament is a ligament in the elbow on the side of the radius. The composition of the triangular ligamentous structure on the lateral side of the elbow varies between individuals and can be considered either a single ligament, in which case multiple distal attachments are mentioned and the annular ligament is described separately, or as several separate ligaments, in which case parts of those ligaments are described as indistinguishable from each other. In the latter case, the ligaments are collectively referred to as the lateral collateral ligament complex, consisting of four ligaments: the radial collateral ligament, from the lateral epicondyle to the annular ligament deep to the common extensor tendon the lateral ulnar collateral ligament, from the lateral epicondyle to the supinator crest on the ulna. Near the attachment on the humerus this ligament is indistinguishable from the RCL and can be considered the posterior portion of it.
Martin 1958 described the distal part of the LUCL as "a definite bundle which crosses the annular band and gains attachment to the supinator crest to a special tubercle on that crest" but didn't name it. The annular ligament, from the posterior to the anterior margins of radial notch on the ulna, encircles the head of radius and holds it against the radial notch of ulna. the accessory lateral collateral ligament. From the inferior margin of the annular ligament to the supinator crest
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