Humeroulnar and Humeroradial Joints
The humeroulnar and humeroradial joints, which make up the medial and lateral sides of the elbow joint, are considered to be a modified-hinge compound synovial joint (Figs. 5.1 and 5.2). The proximal joint surface of the humeroulnar joint consists of the convex, hourglass-shaped trochlea located on the anterior medial surface of the distal humerus. The distal joint surface is the concave trochlear notch on the proximal ulna.
An anterior view of the right elbow showing the humeroulnar and humeroradial joints.
A posterior view of the right elbow showing the humeroulnar and humeroradial joints.
The proximal joint surface of the humeroradial joint is the convex capitulum located on the anterior lateral surface of the distal humerus. The concave, shallow, cup-shaped surface of the proximal end of the radial head is the opposing joint surface.
The joints are enclosed in a large, loose, weak joint capsule that also encloses the superior radioulnar joint. Medial and lateral collateral ligaments reinforce the sides of the capsule and help to provide medial– lateral stability (Figs. 5.3 and 5.4).1
A medial view of the right elbow showing the medial (ulnar) collateral ligament, annular ligament, and joint capsule.
A lateral view of the right elbow showing the lateral (radial) collateral ligament, annular ligament, and joint capsule.
When the arm is in the anatomical position of full elbow extension and supination, the long axes of the humerus and the forearm form an acute angle at the elbow in the frontal plane. This angle, which is called the "carrying angle" (Fig. 5.5), is the result of the slightly more distal projection of the medial epicondyle and trochlear, than the lateral epicondyle. The carrying angle is approximately 10 to 12 degrees in men and 13 to 17 degrees in women.2,3 However, large interindividual variations are present so that some men have greater carrying angles than do some women.3 Children usually have a smaller carrying angle than adults, with the angle gradually increasing with age until puberty when adult values are attained.4,5 The carrying angle of the dominant arm has been reported to be about 1 to 2 degrees greater than the nondominant arm,6 but others have found no differences3 or have found the angle of the left arm to be slightly greater than that of the right.5 A carrying angle that is greater (more acute) than average is called "excessive cubitus valgus," whereas an ...