Pathology of the distal condyles of the third metacarpal and third metatarsal bones of the horse

This study examined material from Thoroughbred horses, the majority of whic h had been in race training, for evidence of pathology in the third metacar pal (McIII) and third metatarsal (MtIII) bones which might be related to th e occurrence of distal condylar fractures. Whole bone samples were studied and documented by macrophotography prior to macroradiography and computed t omographic (CT) imaging, Microradiographs were made from 100 mu m thick med iolateral sections cut perpendicular to the dorsal and palmar/plantar artic ular surfaces of distal condylar regions of McIII and MtIII. Blocks were pr epared for morphological imaging using the backscattered electron mode of s canning electron microscopy (BSE SEM). Linear defects in mineralised articu lar cartilage and subchondral bone were found in the palmar/plantar aspects of the condylar grooves adjacent to the sagittal ridge, These were closely related to the pattern of densification of the subchondral bone and were a ssociated with intense focal remodelling of the immediately adjacent and su bjacent bone. Parasagittal fractures of the condyles originated in similar defects, A unifying hypothesis for the aetiopathogenesis of these fractures is presented.