No hoof, no horse! The clinical implications of modelling the hoof capsule.

Horses stand on the tips of their middle fingers and toes. In each forelimb, they bear their weight on an adapted fingernail which forms the hoof wall. This hoof wall is strongly attached to the last bone (third phalanx) which, in turn, is tied into the column of support in such a way that the complex locomotory forces received through the hoof capsule are directed up into the limb in alignment with the long axis of the limb. Analysis of the hoof during exercise i n vivo is limited, due to the complexity of the interaction between the numerous anatomical structures involved in this support of the hoof wall. In this issue (p 719), Thomason e t a l. (2002) pursue the subject of analysis of strains in the hoof capsule, employing a finite element model. Why is such a model of potential interest to clinicians and farriers? The treatment of debilitating hoof conditions, such as cracks, infections, bruises, abscesses, navicular syndrome and laminitis, as well as their prevention in the first place, still depends on the skill and experience of the farrier in visualising the best shape of each hoof within a particular horse. The farrier has to guess where and how to trim the hoof and, perhaps, how to form and place the shoe, so that the hoof might be loaded in such a way that it is comfortable, effective and stimulated to grow into the best possible shape. This is an art. Attempts to assist this skill with particular measurements and rules to follow have led to the temporary adoption of many different methods. The horse industry is notorious for its reliance on tradition as well as the many methods of trimming and shoeing that follow a cycle of increasing and decreasing popularity. Why is this so? Perhaps an explanation can be found in our insufficient understanding of how the locomotory system of the horse actually works. This deficient understanding is not from any lack of effort in that direction. Scientists have been trying to elucidate the mechanics of the gait of horses since antiquity (van Weeren 2001). Instead, the lack of a coherent description of the mechanics of the distal forelimb is due to the complexity of the problem of predicting the effects of tiny changes in a system that is under a high degree of local feedback control. Despite being tied together by strong ligaments …