906 



NAVICULAR DISEASE. 



and the process commences. But the course of the disease, and 

 especially its long period of development, contradict this view, 

 though it is a fact that, with few exceptions, the tendon surface 

 is always affected. Smith found disease of the tendon in 99 per 

 cent, of cases. The portion of tendon in contact with the 

 navicular bone at first shows brown-coloured spots, its surface 

 loses its glistening character, and soon shows abrasion. Single 

 fasciculi at the surface of the tendon become ruptured (Fig. 518), 

 partly torn away, and rolled upward. Microscopic examination 

 shows them to have undergone fatty degeneration (Smith). 

 In old cases the tendon may be extensively eroded, and may 



finally rupture. Almost all such 

 changes in the tendon are, how- 

 ever, secondary. Immediately the 

 surface of the navicular bone 

 becomes rough from loss of the 

 fibro-cartilage, a rubbing action, 

 similar to that between the 

 articular surfaces in arthritis 

 deformans, occurs between the 

 navicular surface and the tendon. 

 The fact that the portion of the 

 tendon most frequently affected 

 is that exactly over the ridge of 

 the navicular bone supports this 

 view, though granulation on the 

 navicular bone may not be the sole 

 cause of change in the tendon : 

 rupture of fasciculi may perhaps at times be a primary condition, 

 and seems probable where the disease appears suddenly with severe 

 lameness. Under favourable circumstances, and with long rest, 

 union occurs between the perforans tendon and the navicular bone, 

 being favoured by the granulations of the latter. The portions of 

 tendon thus altered may become ossified. 



Causes. The predisposition to navicular disease probably depends 

 largely on peculiarities of conformation ; hence the hereditary 

 character of the disease, and its tendency to attack more than one 

 foot at the same time. Smith seeks to explain the disease by referring 

 it to faulty development of the bony tissue of the navicular bone. 

 Theoretically nothing can be adduced against this view, but further 

 investigations can alone determine to what extent such peculiarities 

 act as causes of the disease. One argument against it is, that the ' 



■■■'.£i& 



Fig. 518. — Flexor pedis perforans tendon 

 in chronic navicular disease (after 

 Brauell). 



