A Case of Separate os tarsale primum in a Horse

Anatomical variation in the equine tarsus may involve either fusion of the os tarsale primum with the os tarsale secundum or the presence of a separate os tarsale primum. The distal row of tarsal bones is therefore of particular anatomical interest, as an independent first tarsal bone has been only sporadically documented in previous studies. In this study, twelve equine tarsal joints were examined using macroscopic and radiographic methods. In eleven specimens, six tarsal bones were identified, whereas in one specimen (1/12, 8.3%), seven tarsal bones were observed due to the presence of an independent os tarsale primum with an irregular cuboid shape. Radiographic examination confirmed and complemented the macroscopic findings. These results document the morphological characteristics of the distal tarsal region in the examined specimens and may support further anatomical and diagnostic studies of the equine tarsal joint.