58 THE SUPERIOR EXTREMITY 



Ossification of the Proximal Extremity of the Ulna. 

 The formation of the olecranon is due chiefly to the growth of 

 the diaphysis which occurs during childhood. A secondary 

 centre appears in the cartilaginous extremity about the eighth 

 or ninth year. It forms the proximal portion of the olecranon 

 (Fig. 1 8), but, as a rule, it takes no part in the formation of the 

 articular surface of the semilunar notch (greater sigmoid cavity). 

 It joins the shaft about the seventeenth year. 



Dislocation of the elbow is common in childhood; because 

 the bony prominences, which in adults produce an osseously 

 strong joint, are only developing at that period. 



Ossification of the Proximal Extremity of the Radius. 

 In the cartilaginous proximal extremity of the radius a secondary 

 centre appears between four and five, and forms a disc-shaped 

 epiphysis, which joins the shaft between eighteen and twenty. 

 Until this centre begins to enlarge, there is relatively little 

 difference between the circumferences of the head and the neck 

 of the bone. This fact explains the frequency of subluxation 

 of the radius (p. 62) in little children. 



The various epiphyses of the elbow have been described in 

 some detail, as a thorough knowledge of them is necessary for 

 the correct interpretation of radiograms of this region. It is not 

 uncommon for the clear area of epiphyseal cartilage to be mis- 

 taken for the line of a fracture, if there is any history of injury ; 

 and the olecranon has been cut down upon owing to this error. 



Separation of the Epiphysis at the distal end of the 

 humerus is the commonest of the more severe injuries of the 

 elbow region which occur during childhood and adolescence. 

 It may be complicated by fracture across the distal and medial 

 portion of the diaphysis. The displacement of the distal 

 fragment is usually backwards, and, owing to the exceedingly 

 strong attachment of periosteum to epiphyseal cartilage, the 

 periosteum is stripped up from the posterior aspect of the distal 

 part of the diaphysis for a varying distance. Unless the 

 replacement is accurate, the stripped periosteum forms a new 

 shaft to the humerus posterior to the existing one, which remains 

 as a prominent exostosis (Fig. 22), and subsequently interferes 

 with flexion by impinging on the coronoid process. As the 

 cartilaginous extremity is translucent to the X-rays, there may 

 be great difficulty in diagnosing this condition in children of less 

 than three years of age, i.e. before the secondary ossific centres 

 are present. 



