Measuring the Angle of the Dished Hoof Wall

This view shows a normal hoof. The two lines measure the angle of the dorsal aspect of the hoof wall and the dorsal aspect of PIII. The lines are parallel. The angle created by the two red lines is 0°. Therefore we can say that PIII has rotated 0°, or not rotated.

This view shows a rotated hoof. Parallelism has been lost. In this illustration the dorsal hoof wall is straight, making angle measurement simple. The angle created by these two lines is 9°. Theretofore we can say that PIII has rotated 9°. In very recent founder the hoof wall may be nearly straight, as shown here. As time passes and hoof wall grows, curvature will develop in the dorsal aspect of the wall.

This is a cross section view of a chronic foundered hoof. The nature of the curvature (dish) will vary greatly from hoof to hoof. The area shaded orange shows stretched lamellar leaves or the "lamellar wedge". Normally the hoof wall (black) would be straight and the depth of the lamellar leaves would be consistent from coronary band to the ground surface creating parallelism between the hoof wall and the dorsal surface of PIII.
Put your mouse pointer over the illustration above

This view shows a red line representing the angle of the dorsal aspect of PIII and a blue line representing an averaged angle of the hoof wall. Assigning the angle of the curved hoof wall is problematic and somewhat arbitrary. The angle created by these two lines is 16°. Theretofore we can say that PIII has rotated 16°. But this measurement will be different if we choose a different curve average (see bottom illustration).

"Derotating" the toe, removing the dish, is usually done by rasping away the hoof wall until the "new" angle of dorsal aspect of the hoof matches that of PIII.

Radiographically this hoof might appear parallel or "normal". But this is an artificial angle. We could rasp a little more, or a little less, changing the angle accordingly. It is not representative of the true hoof wall.

Removal of the dish has done nothing to address the lamellar wedge or the cause of hoof curvature. While derotation is a legitimate exercise, promoting breakover, it is little more than cosmetic. Derotation does not restore hoof anatomy.

If we had the original hoof wall to measure we would find that we still have 16° of divergence (rotation). Another way to look at this is to consider that each of the lamellar leaves is of the same depth from top to bottom in the normal hoof. In the foundered (rotated) hoof lamellar leaves are stretched, becoming longer as they approach the ground. As the amount of stretching increases so does the amount of rotation.

Measuring a curved hoof wall is problematic. Different practitioners might measure this hoof at any of these angles. The hoof wall does not image well radiographically. When making radiographs lay some sort of radio opaque material along the front of the hoof wall to identify the outside of the hoof wall on the radiograph. This will give at least some meaning to the measurements taken off the film.
Green is at 6°, blue is at 16° and yellow is at 24° of rotation relative to PIII

This all may be something of a mute point. The amount of rotation has little, if any bearing on treatment. However, if we are going to discuss rotation angles we can only give meaning to the discussion by measuring the same things.