Sole depth is routinely measured at the distal tip, or apex, of PIII (Fig. 8). A normal, healthy foot has a sole depth of at least 15 mm.
Based on venographic studies in a wide variety of horses, it is considered that a sole depth of less than 15 mm is clinically significant. In a normal foot, the papillae of the solar corium seem to need a space of at least 10 mm between the palmar surface of PIII and the cornified layer of the sole for adequate vascular filling, and at least 5 mm of cornified sole is required to protect the solar corium. Venograms in horses with a sole depth <15 mm show solar papillae that are bent, compressed, or even absent. This distortion or compression surely inhibits sole growth, creating a vicious cycle of thin, tender soles.
