Morphometric study of the equine navicular bone: age-related changes and influence of exercise

Navicular bones from the four limbs of 95 horses, classified in 9 categorie s, were studied. The effects of age on navicular bone morphometry and histo morphometry were estimated, after adjustment of the data to even out the ef fects of front and rear limbs, morphometrical type, sex, weight, and size. All the external measurements of the navicular bone decreased significantly with increasing age. From the histomorphometrical data, cortical bone volu me decreased with age in most horses, whereas cancellous bone volume and, i n particular, the marrow spaces increased. The increase in the cancellous b one volume could have resulted from tunnelling of the interval part of the cortex, which converted it progressively into a porous trabecular-like stru cture. Trabecular bone volume also decreased with age and the trabecular la ttice changed dramatically to become disconnected in aged horses. These obs ervations corresponded closely to those reported for ageing of the skeletal system in humans. However, in sporting horses, the navicular cortical bone volume increased w ith age and the cancellous bone volume decreased. Exercise appeared to have decreased bone resorption and increased bone formation at the endocortical junction. The cancellous bone architecture was also improved, in that the trabecular lattice and trabecular bone volume remained unchanged in aged sp orting horses. Our findings confirmed that exercise may be good practice to prevent age-related bone loss.