The radiographic development of the distal and proximal double contours ofthe equine navicular bone on dorsoproximal-palmarodistal oblique (upright pedal) radiographs, from age 1 to 11 months

The aim of this study was to monitor the postnatal radiographic development of the proximal and distal double contours and the modelling of the shape of the proximal articular border. In mature horses, the proximal and distal contours of the navicular bone on dorsopalmar dorsoproximal-palmarodistal oblique (upright pedal) radiographs are commonly visualised as 2 lines, one being the articular border and the second representing the border of the c ortex facing the deep digital flexor tendon (flexor border). The shape of t he proximal articular border may be concave, undulating, straight or convex in the mature animal. These shapes have been found to be hereditary and to constitute a predisposing factor in the pathogenesis of navicular disease. This predisposing role may result from a shape dependent distribution of t he biomechanical forces exerted on this region. There is no agreement in th e literature with respect to the moment when the navicular bone takes its m ature radiographic appearance, Upright pedal radiographs of the left front foot of 19 Dutch Warmblood foal s were made at age 1 month and subsequently at intervals of 4 weeks, until the age of 11 months. The distal double contour developed soon after birth and the radiographic visibility of the articular border improved from ill-d efined at 1 or 2 months to clear manifestation at 3 or 4 months. The proxim al double contour developed later. The articular border became usually visi ble at age 3 or 4 months and was clearly visible from age 9 months. The mat ure shape of the proximal articular border usually became recognisable from age 7 months and was always obvious between 9 and 11 months. This developm ent was associated with a gradual modelling of the lateral and medial extre mities of the navicular bone. It was concluded that the navicular bone adopts its mature radiological app earance during the first year postpartum. Considering this early manifestat ion of the mature shape of the proximal articular border and its previously demonstrated inheritance, a force-dependent development of this shape, as predicted by the trajectional theory/Wolffs law, is improbable. The predisp osing role of this shape in the pathogenesis of navicular disease may there fore be explained by a shape-dependent distribution of the biomechanical fo rces exerted on the navicular bone. Considering the potential application o f these findings, from age 1 year shape determination enables identificatio n of the individual and breed susceptibility for the development of navicul ar disease.