282 



APPLIED ANATOMY. 



ELBOW-JOINT. 



By the term elbow -joint is meant the articulation between the humerus above 

 and the ulna and upper surface of the radius below. The articulation between the 

 upper end of the radius and the ulna forms the superior radio-ulnar articulation and 

 does not belong to the elbow-joint proper. As has already been pointed out, the 

 ulna articulates with the trochlea and the radius with the capitellum. 



The elbow-joint is a pure hinge-joint. The articulation between the trochlea 

 and ulna is so shaped as to allow no lateral motion, but only an anteroposterior one. 

 The articulation between the capitellum and upper surface of the head of the radius 



is, on the contrary, a ball-and-socket joint. The 

 socket, it is true, is shallow, but it is perfectly 

 spherical, made so by the rotary movement of the 

 radius in pronation and supination. Hence it fol- 

 lows that the shape and continuity of the upper ex- 

 tremity depends upon the articulation of the ulna 

 with the humerus: it further follows that if the 

 radius be removed from the elbow -joint the forearm 

 would still be held in its proper relation to the arm, 

 but if the ulna be removed the stability of the joint 

 would be lost and the forearm would move in any 

 direction, laterally as well as anteroposteriorly. It 

 is for this reason that injuries involving the medial 

 condyle and trochlea are more liable to be followed 

 by serious disability than are those of the lateral 

 condyle and capitellum. 



The movement of the joint takes place around 

 a transverse axis, which passes from side to side 

 below and in front of the condyles. The forearm 

 can be extended to an angle of 180 degrees, or a 

 straight line, with the arm. It can be flexed to an 

 angle of 30 to 40 degrees. Sometimes it cannot be 

 flexed so much, so 'that if after an injury to the 

 joint the patient can flex the elbow to half a right 

 angle, or 45 degrees, he may be regarded as hav- 

 ing regained a normal amount of motion. 



Carrying Angle. The axis of motion of the 

 joint is not exactly transverse, but slopes slightly 

 from the outside downward and inward. The 

 effect of this is to give a slight obliquity to the 

 motions of flexion and extension. This obliquity 

 is not noticeable except in extreme extension and 

 flexion. When the forearm is completely extended 

 it is seen to lie not in the axis of the arm but to 

 bend outward from the elbow at an angle of 170 

 degrees. This angle is called the ' ' carrying angle, ' ' 

 because by resting the elbow against the side, any article which is carried in the ex- 

 tended hand is kept away from the body. Sometimes the line of the forearm is almost 

 straight with that of the arm, at others the deflection may amount to 15 degrees. It 

 may vary on the two sides and 10 degrees may be considered an average; Woolsey 

 gives 6 degrees as the average. This carrying angle becomes lost in certain cases of 

 fracture of the elbow, as will be pointed out later. As the elbow is flexed the carrying 

 angle disappears (see Fig. 294). 



When flexion is complete the ulna instead of coming up toward the head of the 

 humerus inclines inward at an angle of 10 degrees. Morris states that the hand has 

 a tendency to point to the middle of the clavicle, which would make an angle of 20 

 degrees. This we believe to be too great. 



Fie;. 294. The carrying angle; formed 

 by the deviation outward of the axis of the 

 forearm from the axis of the arm. 



