Hoof Mapping - Locating Internal Anatomy Structures Using External References

Historically, many farriers and hoof care educators have made reference to a ‘Centre Point’ on the bottom of a horse’s foot that correlates to either the distal phalanx or the centre of articulation of the distal interphalangeal joint, or both. There have been several formulas for locating or describing this centre reference point. The majority have been based around the use of the frog apex as a starting point for finding the centre of the foot. For the most part the frog apex has been a fairly reliable guide, as it does not appear to easily lose its relationship to the internal anatomy. However, as the inclusion of a frog apex marker on radiographs has become more popular over the last decade or so, many irregularities have been noted as to the position of the marker with respect to the dorsal, distal border of the distal phalanx. It can be assumed that in some cases the TRUE apex of the frog may not have been adequately indentified prior to inserting the radiograph marker, which would account for some of the irregularities. However, even in cases where a TRUE frog apex was well established, some relational disparity is still noted. Therefore, the use of the frog apex as a sole guide to establishing the location of a centre point of the foot appears to be less than reliable than previously thought.

There have been several methods and measurements used over the last few hundred years for finding the cente point of the foot from the frog apex. The most common and currently most widely used methods employ a measurement of 3/4” to 1” (19–26 mm) back or caudal to the frog apex as the centre of the foot. Again, through a sampling of marked radiographs taken over the last 10–15 years, the measurement of 3/4” (19 mm) caudal to the frog apex frequently falls short of the centre of articulation of the DIP joint. Many times using the distance of 3/4” (19 mm) fails to even reach the confines of the DIP joint. Therefore, when the frog apex is used as the starting point for determining the centre of the foot, the commonly used measure of 3/4” (19 mm) appears to be insufficient in most cases. [...]