The head of the radius has a cylindrical form, and on its upper surface is a shallow cup or fovea for articulation with the capitulum of the humerus. The circumference of the head is smooth; it is broad medially where it articulates with the radial notch of the ulna, narrow in the rest of its extent, which is embraced by the annular ligament.[1]
Head of radius
The radius and ulna of the left forearm, posterior surface. The top is proximal (elbow) and bottom is distal (wrist).
The head of the radius is shaped to articulate with a complex of articular surfaces during both flexion-extension at the elbow and supination-pronation in the forearm:[2]
The head's proximal surface is concave and cup-shaped to correspond to the spherical surface of the capitulum of the humerus. The radius can thus glide on the capitulum during elbow flexion-extension while simultaneously rotate about its own main axis during supination-pronation.[2]
Between the capitulum and the trochlea of the humerus is the capitulotrochlear groove. A semi-lunar surface around the circumference of head is shaped to articulate continuously with this groove.[2]
The capitulum does not extend to the posterior side of the humerus and, consequently, during full elbow extension only the anterior half of the head articulates with the capitulum. In full flexion the head similarly reaches beyond the capitulum to enter the shallow radial fossa on the anterior side of the humerus.[2]
The head is cylindrical to allow axial rotation of the radius, thus to articulate with the annular ligament and the radial notch on the ulna.[3]
However, the head of the radius is not perfectly cylindrical but slightly oval. In anatomical position, its major axis (28 mm (1.1 in)) is directed antero-posteriorly and the shorter axis (24 mm (0.94 in)) lateralo-medially. Even though the annular ligament holds the head firmly in place, the ligament is still flexible enough to allow some stretching while the head rotates within it.[3]
During pronation the radius is rotated so that the head's major axis reaches the radial notch on the ulna. This causes a small but significant lateral displacement of the radius' main axis — equal to half the difference between the two axes of the head (2 mm (0.079 in)) — just enough space to accommodate the radial tuberosity as it being moved medially.[3]
head, radius, head, radius, cylindrical, form, upper, surface, shallow, fovea, articulation, with, capitulum, humerus, circumference, head, smooth, broad, medially, where, articulates, with, radial, notch, ulna, narrow, rest, extent, which, embraced, annular, . The head of the radius has a cylindrical form and on its upper surface is a shallow cup or fovea for articulation with the capitulum of the humerus The circumference of the head is smooth it is broad medially where it articulates with the radial notch of the ulna narrow in the rest of its extent which is embraced by the annular ligament 1 Head of radiusThe radius and ulna of the left forearm posterior surface The top is proximal elbow and bottom is distal wrist DetailsIdentifiersLatinCaput radiiTA98A02 4 05 002TA21211FMA33773Anatomical terms of bone edit on Wikidata Contents 1 Articular surfaces 1 1 Humeroradial joint 1 2 Proximal radioulnar joint 2 Additional images 3 See also 4 ReferencesArticular surfaces editThe head of the radius is shaped to articulate with a complex of articular surfaces during both flexion extension at the elbow and supination pronation in the forearm 2 Humeroradial joint edit Main article Humeroradial joints The head s proximal surface is concave and cup shaped to correspond to the spherical surface of the capitulum of the humerus The radius can thus glide on the capitulum during elbow flexion extension while simultaneously rotate about its own main axis during supination pronation 2 Between the capitulum and the trochlea of the humerus is the capitulotrochlear groove A semi lunar surface around the circumference of head is shaped to articulate continuously with this groove 2 The capitulum does not extend to the posterior side of the humerus and consequently during full elbow extension only the anterior half of the head articulates with the capitulum In full flexion the head similarly reaches beyond the capitulum to enter the shallow radial fossa on the anterior side of the humerus 2 Proximal radioulnar joint edit Main article Proximal radioulnar joint The head is cylindrical to allow axial rotation of the radius thus to articulate with the annular ligament and the radial notch on the ulna 3 However the head of the radius is not perfectly cylindrical but slightly oval In anatomical position its major axis 28 mm 1 1 in is directed antero posteriorly and the shorter axis 24 mm 0 94 in lateralo medially Even though the annular ligament holds the head firmly in place the ligament is still flexible enough to allow some stretching while the head rotates within it 3 During pronation the radius is rotated so that the head s major axis reaches the radial notch on the ulna This causes a small but significant lateral displacement of the radius main axis equal to half the difference between the two axes of the head 2 mm 0 079 in just enough space to accommodate the radial tuberosity as it being moved medially 3 Additional images edit nbsp Elbow joint Deep dissection Posterior view nbsp Elbow joint Deep dissection Posterior view nbsp Elbow joint Deep dissection Posterior view See also editNursemaid s elbowReferences edit nbsp This article incorporates text in the public domain from page 1 of the 20th edition of Gray s Anatomy 1918 Gray s Anatomy 1918 see infobox a b c d Kapandji Ibrahim Adalbert 1982 The Physiology of the Joints Volume One Upper Limb 5th ed New York Churchill Livingstone p 82 a b c Kapandji Ibrahim Adalbert 1982 The Physiology of the Joints Volume One Upper Limb 5th ed New York Churchill Livingstone p 112 Portal nbsp Anatomy Retrieved from https en wikipedia org w index php title Head of radius amp oldid 1031851739, wikipedia, wiki, book, books, library,
