286 



HUMAN ANATOMY. 



Fig. 



I; 



plane anterior to the epicondyles. For these anatomical reasons, neither muscular 

 action (triceps) nor falls on the elbow are so productive of separation of this epiph- 

 ysis in children as of fracture of the olecranon in adults. It is, in fact, one of the 



rarest of epiphyseal disjunctions. The symptoms are very 

 similar to those of fractured olecranon. 



The coronoid process is rarely broken except in cases 

 of dislocation of the forearm backward from falls upon the 

 hand. The mechanism is obvious. The force is applied 

 through the medium of the oblique fibres of the interosseous 

 membrane. The line of fracture is nearer the tip than the 

 base of the process. The insertion of the brachialis anticus 

 tendon in the latter region prevents much displacement of 

 the fragment, and the attachment of the capsule of the 

 joint to its edge insures a sufficient vascular supply for pur- 

 poses of repair. Great proneness to recurrence after re- 

 duction in a case of backward dislocation of the forearm 

 should lead to a suspicion of the existence of this fracture. 



Fracture of the shaft of the ulna alone may occur at 

 any point, and is usually the result of direct violence, as 

 when the arm is raised to protect the head from a blow, 

 or in a fall upon the ulnar side of the forearm. In the lat- 

 ter case, when the ulnar fracture is in the upper third, it 

 is not infrequently associated with forward dislocation of 

 the head of the radius (Fig. 300). 



The subcutaneous position of the ulna renders fracture 

 frequently compound. This accounts for the greater fre- 

 quency of non-union in this bone as compared with the 

 radius. In fracture at the lower third the lower fragment 

 is drawn towards the radius by the pronator quadratus. 



Fractures associated with those of the radial shaft will 

 be considered in relation to the effect of muscular action 

 upon them (page 604). 

 The lower epiphysis of the ulna comprises the articular surfaces on the radial 

 and inferior aspects and the styloid process. It is concave superiorly to fit the 

 rounded lower end of the diaphysis. The level of the epiphyseal line is about one- 

 sixteenth of an inch above the level of that of the radius. This epiphysis is strongly 



Lines of fracture of coro- 

 noid, olecranon, and styloid 

 processes of ulna. 



Fig. 300. 



Fracture of upper third of ulna, with dislocation of radius forward. 



held to the lower epiphysis of the radius by the inferior radio-ulnar ligaments and 

 also by the triangular fibro- cartilage extending from the root of the styloid process 

 to the concave margin of the radius. For that reason, and because of its indirect 

 relation to the hand, the uncomplicated separation of this epiphysis is of great 



