The coffin bone is the wedge shaped bone in the horse's hoof. It's the main bone in the hoof that supports the horse's weight. Many lameness problems seen in horses can be attributed to problems with the coffin bone.
There are many things that can cause the coffin bone to break. A nail or other sharp penetrating wound through the hoof can cause a fracture in the coffin bone. Also, a concussion when violent enough can fracture the coffin bone which is how Chico's fractured. A sharp kick to a steel fence resulted in Chico's coffin bone fracture. But don't forget that in many instances coffin bone fractures can also be attributed to pathological conditions in the bone.
Signs of a fracture vary depending on where the bone is fractured. When the break involves the joint surface there is sudden and severe lameness. Your horse may even tremble and sweat and an increase in pulse and heat in the foot region will be evident. Hoof testers will detect immediate pain over the sole.
When the wings of the coffin bone are involved, lameness is not as noticeable when the horse is standing, however, it becomes more evident when the horse turns on the injured foot. The foot region will be warm and sensitive to pressure. You will still need to x-ray the hoof and have your veterinarian establish that a fracture has indeed occurred.
The foot must be immobilized for the bone to heal which usually means 3 to 9 months of stall rest. Special shoeing is also needed which normally is a full bar shoe with clips behind the quarters. This type of shoe will prevent frog pressure and limit expansion of the foot. This is worn for 3 to 6 months and needs to be reset periodically.
The age of the horse and location of the fracture are major factors in how well the coffin bone fracture will heal. When the wings are fractured, the prognosis is good, and the chances of a complete recovery increase more if the horse is 3-years old or younger. However, if the fracture is in the joint surface the prognosis is much less favorable and the horse may suffer from chronic lameness.