The elbow

The elbow is part of a kinematic chain of joints which runs from the thoracic wall to the fingertips (Smith, Weiss & Lehmkuhl, 1996, pp. 9-10). In this chain, 19 degrees of freedom in planar motions can be identified. This freedom of motion constitutes the mechanical basis for performances of skilled manual activities and the versatility of the upper extremity. Since the elbow contains both convex and concave surfaces on each articulating bone, it is known as a sellar (or saddle) joint. This type of joint permits a large range of motion with an economy of articular surface and reduction in the size of the joint. The unique positioning and interaction of the bones of the elbow joint allow for rotation as well as hinge action.

The bones which form the elbow are the trochlear of the humerus, which sits into the greater sigmoid cavity of the ulna, and allows the movements particular to the elbow joint, i.e. flexion and extension; the lesser, or radial, head of the humerus, which articulates

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nd inserts volarly on the wrist. The axis of motion of the radio-ulnar articulation is represented by a line through the center of the head of the radius proximally and through the center of the head of the ulna distally (Smith, Weiss & Lehmkuhl, 1996, pp. 160-162). Accessory motions of the elbow are small compared to the motions possible in the shoulder, wrist, and fingers. The great stability of the joint is due to the corrugated fit of the trochlear and capitulum of the humerus with the matching surfaces of the ulna and radius, as well as the strong medial and lateral collateral ligaments that blend with the joint capsule both anteriorly and posteriorly. When the elbow is flexed, a slight amount of distraction can be felt if the distal end of the humerus is stabilized and posterior force is applied to the anterior surface of the proximal forearm. Mediolateral joint play movements are also present. At the proximal radio-ulnar joint, dorsoventral gliding of the head of the radius on the capitulum of the humerus can be produced passively. The most mechanically stable position of the elbow is extension, and for the radio-ulnar joints, at five degrees of supination. To analyze the leverage factors of muscles, it i
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Approximate Word count = 1552
Approximate Pages = 6 (250 words per page)

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