908 NAVICULAR DISEASE. 



of the hoof. Williams' view, that the most important factor is the 

 failure to neutralise shock, appears incorrect, because under these 

 circumstances the tendon would escape injury. Finally, it must not 

 be forgotten that uprightness of the pastern may not only be a cause, 

 but also a consequence of the disease. 



Peters explains the fact that horses which stand " over " on the 

 front feet more often suffer from this disease, by drawing attention 

 to the sharper angle made by the flexor pedis when passing over the 

 navicular bone, and directs attention to the circumstance that when 

 the limb is loaded and the os pedis in consequence sinks, that tension 

 in the tendon increases, and, consequently, that greater pressure 

 is exercised on the os naviculare. 



The frequent occurrence of navicular disease in horses with long 

 pasterns is explained by the greater stress thrown on the tendons. 

 On the other hand, obliquity of the pastern is in some respects an 

 advantage, because the flexor perforans takes a straighter course 

 over the navicular bone. 



Excessive pressure on the navicular bone preceding sudden partial 

 rupture of the perforans tendon may give rise to the disease, and 

 was regarded by Fambach as the commonest cause. Moller inclines, 

 however, more to Peters' opinion, viz., that navicular disease is due to 

 slowly-acting influences consequent on change in position between the 

 bones of the limb or between them and the hoof axis, an idea which 

 receives support from the slow character of the change. In riding 

 and carriage horses, initial injury may be occasioned by sudden 

 reining-in, jumping, continued sharp trotting, galloping, and 

 occasionally even by slipping. 



English authors, among them Turner and Goodwin, think it 

 may be caused by long rest, desiccation destroying the elasticity 

 of the hoof and favouring the disease. Moller does not agree with 

 Smith in thinking that continued standing on a particular foot causes 

 the disease. He has often seen laminitis and descent of the os pedis 

 under such conditions, but never navicular disease. Some of the 

 above views may be due to faulty diagnosis and mistaking other 

 conditions for navicular disease, especially considering the favourable 

 course noted by the older English authors, who report 90 per cent, of 

 recoveries. Many practitioners consider that concussion and constant 

 hard work on paved streets are the chief causes of navicular disease. 



In rare cases the disease may be preceded by influenza, pneumonia, 

 or rheumatism, and it has been supposed, without much justification, 

 that during the currency of the primary disease the navicular sheath 

 may become infected. 



