Basic Mechanics of the Digit - Transverse View

by
James Rooney, D.V.M.

In several other essays on this site I have addressed certain aspects of the shape of the hoof primarily from the lateral or side view. That is, of course, quite insufficient. We should like to have a full dimensional view: sagittal (the lateral view), cross sectional (transverse), and frontal (looking at the foot from directly above or below). These views are shown in Fig. 1. The gray panel indicates the cross section view (perhaps better called the transverse view) and the blue the frontal view. The lateral or sagittal view, Fig. 3, is in the plane of the page, the olive panel.

Figure 1

Figure 2

The material in this essay and in Basic Mechanics of the Digit-2. have been done before, but perhaps a repeat is not a bad thing; besides I like it!.

In the this essay we consider the transverse view.

As everyone surely knows the obvious configuration of the hooves as seen from the front is as shown in Fig. 3; the medial (inside) wall is vertical or very nearly so. The lateral (outside) wall is slanted outward.

Figure 3

Our task here is to explain why this shape. It is quite simple and requires no complicated (or simple) mathematics. A somewhat more difficult analysis is given in the appendix.

Figure 4

Fig.4, a transverse view with the two legs and the eccentric position of the weight, -W, between and exerting a downward and inward pull on the two legs. That action tends to collapse the medial walls of the hoof and slant the lateral walls outward. Since this normal action is always present, we can say that the hoof was “built” in order to have the walls lined up with the forces to be expected. Thus, the medial wall is built in line with the downward compressive force while the lateral wall is built in parallel with the slanting compressive force. In this regard please see, as, well Basic Mechanics of the Digit-1.

Please note, as well, that this configuration assures that the horn tubules in the hoof wall are parallel to the force being experienced by the hoof wall. All this has been expressed in a grievously teleological way, suggesting that the hoof knows what is going to happen and gets ready for it!

We avoid this teleological explanation by examining newborn and otherwise still young animals. These young hooves are nearly symmetrical in the cross section view. The orientation described above is acquired as the animal grows and gains weight and is, therefore, an acquired state, the hoof assuming that shape which best fits the forces applied to it.

Appendix

This appendix gives a more definitive explanation for the shape of the hoof in the transverse view. The footnote may be of interest as well to the geometrically minded.^[1]

Figure 5

This looks horrible but really isn’t so bad. We are looking at the horse from the front with the left fore (lf), right fore (rf), center of mass (cm), body weight (-W), and the reaction of the rf (W) to –W. Now by the trickery of vector mechanics we can show that the down motion of the cm can be represented by two force vectors, in red, one to each foreleg. (We are just doing this for the right fore, the dashed red vector to the left fore only indicating that the same thing is repeated there.)

Actually, we use the red vector to the outer part of the right fore hoof and the green vector to the inside part. The vertical force is the same both outer and inner (and in fact all the way across) as indicated by the vertical red and green vectors. The force directed outward, laterally, the horizontal vectors, is larger on the outside of the foot and smaller on the inside. If we move the two resultant vector ^[2] forces, red and green, down to the right in the picture, it is apparent that we approach rather well the transverse appearance of the hoof.

Footnotes:

^[1] The transverse view is mimicked very well by the geometric figure: a trapezium.

^[2] A resultant vector is the “result” of adding two vectors together, in this case the vertical vector and the horizontal vector.

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