Radiographic study of the sound navicular bone. Part 1: What about the canals on the distal border

The scoring system based on the different types of navicular distal border canals is a good method to quantify and relativise the anomalies in number, shape and localisation of the canals. The distal border score varies significantly with the limb (fore or rear), the morphological type, the gender and the age of the horse. These anatomical variations are of importance and must be taken into account when examining a suspect bone. The score is larger for the fore navicular bone than for the rear. It could be interesting to compare both scores: rear navicular bone score is generally equal to half (or slight less) that of the fore. The score is larger for heavy types of horses and ponies (drafthorse, heavy halfbreds and Fjords). This phenomenon could be related to a larger pressure within the distal interphalangeal joint. The score is lower for the athletic halfbred than for other half-breds. This could be the result of the changes in bone architecture induced by exercise and particularly bone densification. The score is lower for the female than for the male. We think that navicular bone quality is better for the female and this idea corroborates that of other authors that consider that the risk to develop navicular disease is smaller for the female than for the male. The score increases with age. It is particularly small in young horses less than two years old and then increases strongly. This phenomenon is to be related to the progressive development, in the first year of life, of the groove between articular cartilage and distal impar ligament, canals developping only later one. In athletic horses, the score is higher between 7 and 12 years of age. During this time, we also observe more degenerative changes within the navicular bone, which could mean that bone is of lesser quality