THE RADIO-ULNAR ARTICULATIONS. 353 



usuall.v of tubercular origin, is of common occurrence in the elbow-joint : under these circum- 

 stances the forearm tends to assume the position of semi-flexion, which is that of greatest ease 

 and relaxation of ligaments. It should be borne in mind, that should ankylosis occur in this or 

 the extended position, the limb will not be nearly so useful as if ankylosed in a position of rather 

 less than a right angle. Loose cartilages are sometimes met with in the elbow-joint, not so 

 commonly, however, as in the knee ; nor do they, as a rule, give rise to such urgent symptoms 

 as in this articulation, and rarely require operative interference. The elbow-joint is also some- 

 times affected with osteo-arthritis. but this affection is less common in this articulation than in 

 some other of the larger joints. 



Excision of the elbow is principally required for three conditions : viz. tubercular arthritis, 

 injury and its results, and faulty ankylosis ; but may be necessary for some other rarer condi- 

 tions, such as disorganizing arthritis after pyaemia, unreduced dislocations, and osteo-arthritis. 

 The results of the operation are. as a rule, more favorable than those of excision of any other 

 joint, and it is one. therefore, that the surgeon should never hesitate to perform, especially in 

 the first three of the conditions mentioned above. The operation is best performed by a single 

 vertical incision down the back of the joint, a transverse incision, over the outer condyle, being 

 added if the parts are much thickened and fixed. A straight incision is made about four 

 inches long, the mid- point of which is on a level with and a little to the inner side of the tip of 

 the olecranon. This incision is made down to the bone, through the substance of the Triceps 

 mus -le. The operator with the point of his knife, and guarding the soft parts with his thumb- 

 nail, separates them from the bone. In doing this there are two structures which he should 

 carefully avoid : the ulnar nerve, which lies parallel to his incision, but a little internal, as 

 it courses down between the internal condyle and the olecranon process, and the prolongation of 

 the Triceps into the deep fascia of the forearm over the Anconeus muscle. Having cleared the 

 bones and divided the lateral and posterior ligaments, the forearm is strongly flexed and the 

 ends of the bone turned out and sawn off. The section of the humerus should be through 

 the base of the condyles. that of the ulna and radius should be just below the level of the 

 les<t r sigmoid cavity of the ulna and the neck of the radius. In this operation the object is 

 to obtain such union as shall allow free motion of the bones of the forearm ; and, therefore, 

 passive motion must be commenced early, that is to say, about the tenth day. 



VI. Radio-ulnar Articulations. 



The articulation of the radius with the ulna is effected by ligaments which 

 connect together both extremities as well as the shafts of these bones. They may, 

 consequently, be subdivided into three sets : 1, the superior radio-ulnar, which is 

 a portion of the elbow-joint; 2, the middle radio-ulnar; and, 3, the inferior radio- 

 ulnar articulations. 



1. SUPERIOR RADIO-ULNAR ARTICULATION. 



This articulation is a trochoid or pivot-joint. The bones entering into its 

 formation are the inner side of the circumference of the head of the radius rotating 

 within the lesser sigmoid cavity of the ulna. Its only ligament is the annular or 

 orbicular, 



The Orbicular Ligament (Fig. 246) is a strong, flat band of ligamentous fibres, 

 which surrounds the head of the radius, and retains it in firm connection with the 

 k-.-M.-r sigmoid cavity of the ulna. It forms about four-fifths of a fibrous ring, 

 attached by each end to the extremities of the lesser sigmoid cavity, and is smaller 

 at the lower part of its circumference than above, by which means the head of the 

 radius is more securely held in its position. Its outer surface, is strengthened 

 by the external lateral ligament of the elbow, and affords origin to part of the 

 Supinator brevis muscle. Its inner surface is smooth, and lined by synovial 

 membrane. The synovial membrane is continuous with that which lines the 

 elbow-joint. 



Actions. The movement which takes place in this articulation is limited to 

 rotation of the head of the radius within the orbicular ligament, and upon the 

 lesser sigmoid cavity of the ulna, rotation forward being called pronation; rotation 

 backward, xii^'mat'inn. Supination is performed by the Biceps and Supinator 

 brevis. assisted to a slight extent by the Extensor muscles of the thumb and, in 

 certain positions, by the Supinator longus. Pronation is performed by the Pro- 

 nator radii teres and the Pronator quadratus, assisted, in some positions, by the 

 Flexor carpi radialis. 



Surface Form. The position of the superior radio-ulnar joint is marked on the surface of 



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