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You are watching: The antebrachium is composed of which two bones

StatPearls . Endowment Island (FL): StatPearls Publishing; 2021 Jan-.


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Anatomy, Shoulder and also Upper Limb, Forearm Radius

Michael M. Bair; Anoosh Zafar Gondal.

Author Information

Introduction

The radius is just one of two long bones that consist of the person antebrachium, the other bone gift the ulna. The radius has actually three borders, three surfaces, and also has a prismoid shape in i m sorry the base is more comprehensive than the anterior border. The radius articulates proximally in ~ the elbow v the capitulum of the humerus and also the radial notch the the ulna. It articulates in ~ its distal finish with the ulna in ~ the ulnar notch and with the articular surface of the scaphoid and lunate carpal bones. 

The most proximal segment the the radius is the radial head. The head is cylindrical and also contains the articular disc i m sorry articulates v the humeral capitulum and also radial notch of the ulna. Distal to the radial head is the neck of the radius and also radial tuberosity - an oval prestige that is the website of attachments of the biceps brachii muscle. Distal to the radial tuberosity is the column of the radius wherein multiple muscles attach, including the pronator teres, pronator quadratus, supinator, and extrinsic hand muscles.<1>

 Fractures of the distal radius account for several of the most usual low-energy fractures checked out in ambulatory orthopedics accounting for between 8% and 15% of every bone-related injuries in adults.<2> It is 2nd only come the hip together the most commonly broken bone in the elderly.<3> Additionally, the subluxation of the annular ligament i beg your pardon stabilizes the proximal radius is an injury frequently seen through pediatricians. 


Structure and also Function

Function:

The radius permits the forearm and hand to pronate and also supinate, flex and extend at the elbow, and adduct, abduct, extend, flex, and also circumduct the wrist. Pronation and also supination occur through complex articulation through the cylindrical shaped radial head, i beg your pardon is stabilized to the ulnar notch through the annular ligament. This arrangement enables the radial head to turn proximally, causing anteromedial activity of the distal radius. The distal radius the cross over the distal ulna and also inverts to allow the wrist and hand come pronate. A reversal of this movement allows for supination. 

In addition to pronation and supination, three articulations permit for extension and flexion in ~ the elbow joint. The elbow joint is a pivot joint (radiocapitellar articulation), a hinge joint (humeroulnar articulation), and also a second pivot joint (proximal radioulnar joint). The radius also articulates with the capitulum of the humerus. The olecranon of the ulna articulates with the trochlea of the humerus enabling for the antebrachium come flex and extend with the brachium. While the proximal radioulnar joint"s primary duty is to allow pronation and also supination, the annular ligament maintains proximity between the two bones as the biceps and brachialis contract, causing flexion and permitting the 2 bones to relocate as one unit.

Distally, the ulnar notch the the radius and also the ulnar head articulate at another pivot joint permitting for supination and also pronation. The radius articulates through the wrist via the scaphoid and also lunate bones. This articulation is a condyloid or "ellipsoidal" joint which permits the wrist to relocate in two planes. The radiocarpal joint enables the wrist come adduct, abduct, flex, extend, and circumduct.<4>

Joints and Ligaments:

The lateral ligaments that the elbow are collectively named the lateral collateral ligament complex, i beg your pardon is written of 4 ligaments the are difficult to separate. First, the lateral collateral ligament (a.k.a. "radial collateral ligament") attaches native the lateral epicondyle that the humerus to the annular ligament. The lateral collateral ligament join the radius to the humerus and also protects the antebrachium versus varus stress. The annular ligament attaches from anterior to the posterior radial notch the the ulna encircling the radial head enabling pronation and also supination. The lateral ulnar collateral ligament attaches indigenous the lateral epicondyle of the humerus come the ulnar supinator crest. The lateral ulnar collateral ligament helps safeguard the antebrachium versus valgus stress. Finally, the accessory lateral collateral ligament attaches from the supinator crest come the worse margin of the annular ligament, providing additional stability to the joint.<5>

Between the medial border the the radius and the lateral border of the ulna resides the interosseous membrane i beg your pardon divides the anterior and also posterior compartments of the antebrachium. The interosseus membrane serves as an attachment website for muscle while permitting for force distribution throughout the forearm. When the forearm supinates, the interosseous membrane fibers come to be taught, stabilizing distal and proximal joints.<6> prefer the lateral collateral ligament complex, the composition of the interosseous membrane is of multiple ligaments that are an overwhelming to separate. The 5 ligaments the the interosseous membrane are the proximal slope cord, accessory band, main band, dorsal oblique accessory cord, and the distal tilt bundle.<7>

The distal radioulnar articulation is created of the palmar radioulnar ligament (volar radioulnar ligament) that attaches the anterior radius to the anterior ulna, the dorsal radioulnar ligament (posterior radioulnar ligament) i m sorry attaches the posterior radius to the posterior ulna, and the articular disc which lies in between the distal ulna and radius. These structures allow for load circulation and permit the second pivot throughout pronation and supination that the forearm.

The distal radius is attached to the lunate bone via 2 ligaments, the long and also short radiolunate ligaments. These ligaments stop hyperextension the the lunate bone throughout wrist extension. The distal radius is attached to the scaphoid via the radial collateral ligament the the wrist, and the radioscaphocapitate ligament attaches the volar facet of the radius come the scaphoid and also capitate carpal bones. Lastly, the dorsal radiotriquetral ligament is a vast ligament, which connect the dorsal radius to the dorsal scaphoid, lunate, and triquetrum.

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Borders and Surfaces:

The radius has actually three boundaries (volar, dorsal, and also internal) and also three surfaces (volar, dorsal, and lateral). The volar border the end the lateral and volar surfaces, the dorsal border off the lateral and also posterior surfaces, and also the inner (interosseous border) the end the volar and also dorsal surfaces.  

The volar surface ar (anterior surface) offers the site of origin to the flexor pollicis longus and flexor digitorum superficialis muscles, and also site that insertion to the pronator quadratus, supinator, and also biceps brachii muscles. It also provides the surface for the anterior radiocarpal ligament attachment. The dorsal surface offers the beginning site come the abductor pollicis longus and extensor pollicis brevis muscles as well as the insertion because that the remainder of the supinator muscle. The lateral surface provides the insertion sites because that the brachioradialis and pronator teres muscles. These room generalizations of where each muscle attaches, and also in enhancement to anatomical variation, plenty of of the muscles attach to an ext than one radial surface.<10><11>