Canine tarsal architecture as revealed by high-resolution computed tomography

Central tarsal bone (CTB) fractures are well documented and are a subject of increasing importance in human, equine and canine athletes although the mechanism of these fractures in dogs is not fully understood and an extrapolation from human medicine may not be accurate. This study reports the use of high-resolution computed tomography (CT) of 91 tarsal joints from 47 dogs to generate a more detailed in situ anatomical description of the CTB architecture in order to obtain a better understanding of the pathogenesis of CTB fractures in this species. The dogs studied represented a wide range of ages, breeds and levels of habitual physical activity and the angles of the tarsal joints studied ranged between maximal flexion (16.4°) and maximal extension (159.1°). Regardless of tarsal angle, the CTB articulated with the calcaneus exclusively at the level of its plantar process (PPCTB) in all dogs. The PPCTB presented two distinct parts in all dogs, a head and a neck. The calcaneus tended to rely on the PPCTB neck during flexion and on the PPCTB head during extension. This study describes new tarsal elements for the first time, including the calcaneal articular process, the fourth tarsal bone plantar articular process and the talar plantar prominence of the CTB. Based on calcaneo-PPCTB architecture, it is postulated that the PPCTB is a keystone structure and that at least some of CTB fractures in dogs could either commence at or are induced at this level due to the impingement forces exercised by the calcaneus.