Relationships of age and shape of the navicular bone to the development of navicular disease: a radiological study.

Estimating the shape of the proximal articular border of the navicular bone and grading the radiological navicular bone condition (grades 3 and 4 representing the most severe changes), the aim of this study was to assess potential age-related implications of the previously reported shape predisposition to navicular disease in 746 normal and 174 clinically affected Dutch Warmbloods age 3-19 years. A significant, age-independent, shape-grade association found in normal and affected horses emphasises the fundamental character of the shape predisposition to navicular disease. A significant age-related increase of the least susceptible shape prevalence was found in elderly normal horses. A shape-independent low grades 3 and 4 prevalence (mean 15%) was found in normal horses, vs. a high grades 3 and 4 prevalence (mean 85%) in the affected horses. Therefore, the clinical manifestation of the disease is grade-rather than shape-dependent. A significant age-related appearance of inverted flask-shaped channels and enthesophytes was found in the clinically affected horses. However, considering the significant shape-radiological features association previously reported in 3-year-old normal horses, this association may be shape- rather than age-dependent.