Structural variation of the distal condyles of the third metacarpal and third metatarsal bones in the horse

This study examined 3-dimensional (3D) distribution of sectors with contras ting density in the equine third metacarpal (McIII) and third metatarsal (M tIII) bones with a view to explaining the aetiology of distal condylar frac tures. Macroradiography and computed tomographic (CT) imaging were used in the nondestructive study of bones obtained from horses, most of which were Thoroughbreds in race training. Distal condylar regions of McIII and MtIII were also studied in microradiographs of 100 mu m thick mediolateral sectio ns cut perpendicular to the dorsal and palmar/plantar articular surfaces. Q ualitative and quantitative results from all methods used (radiography, CT and microradiographic stereology) demonstrated densification (sclerosis) of subchondral bone located in the palmar/plantar regions of the medial and l ateral condyles of both McIII and MtIII, Substantial density gradients betw een the denser condyles and the subchondral bone of the sagittal groove wer e shown to equate with anatomical differences in loading intensity during l ocomotion. It is hypothesised that such differences in bone density results in stress concentration at the palmar/plantar aspect of the condylar groov es, which may predispose to fracture.