NAVICULAR DISEASE. 905 



of the navicular bone seems to be the commonest point of origin. 

 Both the course and character of the process support this view. 

 Little spots no larger than a millet-seed are to be found here, generally 

 about the centre of the middle elevated portion, over which the fibro- 

 cartilage appears coloured (Figs. 516 and 517). Smith views these 

 as calcareous deposits, but microscopic examination reveals the 

 same conditions as in arthritis deformans, i.e., proliferation of 

 cartilage cells, with fibrillation of the intercellular substance. The 

 cartilage thus altered loses its consistence and becomes eroded 

 (Fig. 517). 



As soon as the substance of the bone is attacked, granulations 

 form, causing destruction of neighbouring portions of cartilage and 

 of bone. Rarefying ostitis sets in ; the compact tissue, normally 

 of a yellowish-white, assumes a reddish colour, and disappears more 



Fig. 517. — Navicular bone in chronic navicular disease (after Brauell). 



and more in consequence of increasing proliferation of the medullary 

 tissue. The bone may thus be so much weakened as readily to fracture 

 under pressure of the tendon. Smith states having seen, in certain 

 cases, changes in the compact tissue precede those in the cartilage : 

 this is more frequent where both feet suffer. As a rule, these peculiar 

 osteophytes, which resemble those of arthritis deformans, and appear 

 as though poured out on the surface, can be found on the margins 

 of the navicular bone, and especially on the upper margin, where 

 the bursa extends from the tendon on to the bone. The ligaments 

 of the navicular bone become thickened and sometimes ossified. 

 The upper surface of the bone, which contributes to the formation 

 of the coffin-joint, is never thus affected. 



When the condition is preceded by bursitis, which Williams 

 considers common, the parts are more or less reddened and injected, 

 and the bursa is thickened and its surface roughened. Such disease 

 must, of course, affect the tendon and navicular bone. 



Finally, inflammation may extend from the flexor perforans 

 to the navicular bone ; Fambach, indeed, regards this as the rule. 

 Isolated fasciculi of the tendon are ruptured by excessive strain, 



