Are Distal Border Fragments of the Navicular Bone of Clinical Significance?

Fragments of the distal border of the navicular bone are identified radiologically with low frequency in horses free from lameness. There is higher frequency of occurrence in horses with foot pain, especially navicular disease. The clinical significance of a fragmentper se is controversial. There is limited knowledge about the progression of the lesion and/or lameness. The pathogenesis of fragments is not completely clarified; avulsion fracture or pathological fracture of the navicular bone, fracture of an entheseophyte at the origin of the distal sesamoidean impar ligament (DSIL), or dystrophic mineralisation within the DSIL have been proposed.

Radiological identification of fragments is challenging and in a recent study there was only fair agreement between experienced observers (Groth et al. 2009). Fragments are usually positioned at the junction between the distal horizontal and sloping borders of the navicular bone and are easiest to detect on well-positioned dorsoproximal-palmarodistal oblique images. We routinely acquire 2 projections, obtained with a slightly different angle of the hoof wall, to reduce the risk of missing potentially significant lesions. [...]