| Humeroradial joint | |
|---|---|
 Leftelbow-joint, showing anterior andulnar collateral ligaments | |
| Details | |
| Identifiers | |
| Latin | articulatio humeroradialis |
| TA98 | A03.5.09.003 |
| TA2 | 1774 |
| FMA | 38855 |
| Anatomical terminology | |
Thehumeroradial joint is thejoint between thehead of theradius and thecapitulum of thehumerus, is a limitedball-and-socket joint, hinge type ofsynovial joint.
Theannular ligament binds the head of the radius to theradial notch of theulna, preventing any separation of the two boneslaterally. Therefore, the humeroradial joint is not functionally aball and socket joint, although the joint surface in itself allows movement in all directions.
The annular ligament secures the head of the radius fromdislocation, which would otherwise tend to occur, from the shallowness of the cup-like surface on the head of the radius. Without this ligament, thetendon of thebiceps brachii would be liable to pull the head of the radius out of the joint.
The head of the radius is not in complete contact with the capitulum of the humerus in all positions of the joint.
The capitulum occupies only theanterior andinferior surfaces of the lower end of the humerus, so that in complete extension a part of the radial head can be plainly felt projecting at the back of the joint.
In fullflexion the movement of the radial head is hampered by the compression of the surrounding soft parts, so that the freest rotatory movement of the radius on the humerus (pronation andsupination) takes place in semiflexion, in which position the two articular surfaces are in most intimate contact.
Flexion andextension of the elbow-joint are limited by the tension of the structures on the front and back of the joint; the limitation of flexion is also aided by the soft structures of the arm and forearm coming into contact.
A subluxation of the humeroradial joint is called a "nursemaid's elbow", also known asradial head subluxation.[1] It is generally caused by a sudden pull on the extendedpronated forearm, such as by an adult tugging on an uncooperative child or by swinging the child by the arms during play.
In radial headsubluxation, there is little complaint of pain, and the person generally reports pain in the proximalforearm. The mechanism is slippage of the head of the radius under the annular ligament. The distal attachment of the annular ligament covering the radial head is weaker in children than in adults, allowing it to be more easily torn. The older child will usually point to the dorsal aspect of the proximal forearm when asked where it hurts. This may mislead one to suspect a buckle fracture of the proximal radius.[2] There is no tear in the soft tissue (probably due to the pliability of young connective tissues).[2]
Aradial head dislocation is mainly caused by trauma, or by a congenital state. The traumatic form is usually seen in infancy and childhood as an isolated injury.[3]
![The radiocapitellar line is used in the detection of radial head dislocation on lateral X-rays. It normally goes through the capitulum of the humerus.[4]](/mt/?noimg=&dark=on&url=https%3a%2f%2fwikipedia.org%2fwiki%2fFile%3aRadiocapitellar_line_-_normal.jpg)
![Abnormally pointed radiocapitellar line, indicating radial head dislocation.[4]](/mt/?noimg=&dark=on&url=https%3a%2f%2fwikipedia.org%2fwiki%2fFile%3aRadiocapitellar_line_-_abnormal.jpg)
This article incorporates text in thepublic domain frompage 321 of the 20th edition ofGray's Anatomy(1918)
