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Q: How much bone remodeling can we expect to take place on a 10-year-old horse with prominent splaying out of the front feet after we remove extra horn from the bottom along the outside edge of the hoof?
A: Bones maintain themselves as a balance between bone loss and new bone deposition. In bone remodeling, the bone loss wins out in one area and the new bone deposition wins out in another. It is not the bone bending as it almost seems to be on radiographs.
Remodeling occurs in response to mechanical forces on the bone. Generally, abnormal pressure causes resorption, and tension causes bone deposition. Pressure from the sole accounts for the bone loss on the ground surface, and the splayed out wall levering away from the bone accounts for the bone deposition forming the ski tip.
If the palmar edge of P3 is weight bearing without the support of the hoof wall, rapid bone resorption occurs. We see this in club-footed horses, foundered horses and horses without enough hoof wall to suspend the coffin bone. In a horse with a coffin bone that is rotated toward the ground, the dorsal tip forms the typical ski-tip curve. This happens with horses with club feet or founder, those trimmed too short in the toe and sometimes those with heels left too high.
If the whole bottom edge comes into weight bearing, then a more subtle bone resorption occurs resulting in a general loss of concavity around the solar margin.