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ch06.qxd 3/22/04 80 3:59 PM Page 80 Chapter 6 Table 6-1. PHYSIOLOGIC MOTION Physiological Movement of the Humeroradial Joint Direction of Slide of the Radius on Capitulum Flexion Anterior Extension OF THE ELBOW Physiologic Motion of the Radius Direction of Slide of the Distal Radius on the Ulna When you pronate The radial head moves posteriorly (dorsal) Posterior When you supinate The radial head moves anteriorly (volar) Physiological Movement of the Ulna Direction of Slide of the Ulna on the Trochlea Physiologic Motion of the Radius Direction of Slide of the Distal Radius on the Ulna Flexion Distal/anterior Varus angular with elbow Lateral Pronation Anterior (volar) Supination Posterior (dorsal) flexion Extension Proximal/posterior Valgus angulation with Medial elbow in extension at the elbow or in providing additional stability to the joint. The resting position of the proximal radioulnar joint is 35 degrees of supination and 70 degrees of elbow flexion. The position of greatest stability (close packed position) is in 5 degrees of supination. The primary muscles involved at the radioulnar joint are the supinator and the pronator quadratus. Arthrokinetics With pronation and supination of the forearm, the direction of slide of the proximal radius on the ulna is opposite to the motion. This is because the convex rim of the radial head articulates with the concave radial notch on the ulna. With rotation of radius, the convex rim moves opposite to the bone motion (Kisner & Colby, 1990) (see Table 6-1). Inferior (Distal) Radioulnar Joint This joint is at the distal end of the forearm near the wrist where the ulnar notch of radius articulates with the head of the ulna. This is an extremely stable joint due to the articular disk, the interosseus between the radius and ulna and the pronator quadratus muscle. Osteokinematics Like the proximal radioulnar joint, the distal radioulnar joint is a uniaxial pivot joint. In order to produce pronation and supination, the distal end of the radius must be free to move about the ulna at its distal end as well as at the proximal portions (Jenkins, 1998). Rotation of the lower end of the radius around the head of the ulna occurs at the distal radioulnar joint. The resting position is in 10 degrees supination, and close packed position is in 5 degrees supination. Arthrokinetics The articulating surface of the radius slides in the same direction as the bone motion because the concave ulnar notch on the distal radius articulates with the convex portion of the head of the ulna (Kisner & Colby, 1990) (see Table 6-1). MOVEMENTS AT THE ELBOW JOINT Flexion and Extension The flexion and extension movements that occur at the humeroradial and humeroulnar joints are primarily gliding motions until the last 5 to 10 degrees, when the surface joint motion changes to rolling. The rolling in flexion occurs when the coronoid process of the ulna comes into contact with the floor of the numeral coronoid fossa. During flexion, there is distal (inferior) glide of the ulna in the trochlea. Supination and adduction of the ulna in the trochlea and distal movement and pronation of the radius on the humerus also occurs at the same time (Hamil & Knutzen, 1995). The capsule limits flexion more than extension and total range of elbow flexion ranges from 135 to 146 degrees.