comes a single stress concentrator, the stress is focused at this one site, and the rate of damage increases.10 When one fracture begins to predomi- nate, it is difficult for the horse to remodel the bone fully enough to eliminate the stress concentration; therefore, surgery to accelerate the remodeling and promote healing is beneficial.23 Because the stiffness of the older bone of the year- ling metacarpus is greater than the newly formed
Fig. 3. Stress fracture propagated from the dorsal cortex into the medullary cavity. The horse was removed from training and stall-rested. The periosteal callus covers the exit of the fracture on the dorsal cortex, but the deep remodeling of the fracture is incomplete. Surgical treatment is often elected because of the prolonged remodeling time necessary for stress fracture healing.
overloaded before it can become strong enough to neutralize the damage (Fig. 4). Stress fractures are part of the modeling process, though they do not become radiographically apparent in most horses. Multiple stress fractures are easier for the horse to overcome than is a single fracture that begins to predominate. In the presence of multiple fractures, the stress of loading is divided among many frac- tures. If one fracture begins to predominate, it be-
Fig. 4. Radiograph of the metacarpus shows multiple stress fractures developing in the newly formed bone because the train- ing is proceeding faster than the newly formed bone can be formed and strengthened in response to training.
