Radiographic anatomy of the equine distal tibia

The radiographic anatomy of the equine distal tibia is complex and is not widely described in the current literature. Superimposition and radiographic similarities between the different osseous structures of the equine distal tibia can make it difficult for anatomic localization of pathology. The purpose of this prospective, descriptive, anatomic study was to detail the normal anatomy of the equine distal tibia using routine radiographic projections and CT of the equine tarsus. Radiographic identification of the different osseous protuberances of the distal tibia on three cadaveric limbs was achieved using radiopaque markers and evaluation of multiplanar and 3D CT reconstructions to create anatomical maps. It was found that the lateral malleolus is composed of cranial and caudal protuberances that are superimposed over the intermediate cochlear ridge of the distal tibia on the lateromedial, dorsal 45° lateral-plantaromedial, and dorsal 65° medial-plantarolateral oblique views, thereby hindering visualization of the cranial protuberance of the lateral malleolus. The medial malleolus is a simple rounded protuberance with discrete margins. On the dorsal 65° medial-plantarolateral oblique, the medial malleolus is ill-defined due to superimposition with the talus. The intermediate cochlear ridge of the distal tibia extends in a craniolateral to caudomedial direction, with its cranial protuberance largely superimposed with the calcaneus and talus on the dorsoplantar view. In summary, the distal tibial anatomy is complex and a thorough anatomical reference is necessary when reviewing radiographs of the equine tarsus for pathology. A plantaro 15° distal 85° lateral-dorsoproximomedial oblique projection is proposed to isolate all distal tibial protuberances.