A lame horse A 3 year old Swiss mountain horse had been lame for 2 months - there was no history of an injury - the horse was not being used for any athletic activity but was pastured in a large open area where she was seen only occasionally. On physical examination, the soft tissue around the coronary band was firm on palpation and pain could be elicited on flexion and extension of the distal interphalangeal joint. Radiographs were made of P3 and the navicular bone. Radiographic changes The routine study of P3 and the navicular bone included a 45 degree dorsopalmar, 60 degree dorsopalmar, lateral, and “skyline” view of the navicular bone - in addition, two obliques of the 60 degree dorsopalmar study were made. The navicular bone on the lateral view has an abnormal shape of the proximal border with new bone formation. The 60 degree DP views show the marked destructive changes in the navicular bone - the lesions on these views suggest they are poorly defined and within the medullary cavity (arrows). The skyline view is most important since it show the destructive lesions to be within the flexor cortex with extension into the medullary cavity - the largest lesion is present both medially and laterally to the sagittal ridge being larger laterally (arrows) - smaller separate medullary cysts are poorly defined. The destructive pattern varies from that seen with typical navicular bone disease - in this horse, the destruction centers on the flexor cortex and appears to expand into the medullary cavity - it is probably secondary to infection of the navicular bursa often subsequent to a penetrating wound . The radiographic changes are chronic in appearance, but the level of activity of osteomyelitis or infectious navicular busitis is difficult or impossible to determine from the radiograph.
