The coffin bone, also known as the pedal bone, third phalanx, distal phalanx, and os pedis
, is located in the horse's foot. It is completely encompassed by the hoof wall, and is where the horse's body weight rests as a pressure-force before it is transferred to the hoof plate. Coffin bone fractures can occur a number of ways, some of the most common being:
- Stepping on a rock
- Exercising or getting turned out in areas with very hard or irregular surface, such as dried clay, rocky, or frozen ground
- Kicking at a stall wall
- Jumping and coming down very hard, or at an angle
Coffin bone fractures can occur along the wing (side), center (body), extensor process, or solar margin (perimeter) of the coffin bone.
Clinical Presentation of Horses with Coffin Bone Fractures
The degree of lameness in affected horses varies depending on the location of the fracture. Extensor process and solar margin fractures usually result in slight lameness (grade 1-2 of 5), where center and wing fractures tend to cause moderate to severe lameness (grade 4-5 of 5). Since the coffin bone is completely enclosed within the hoof capsule, there will not be any swelling or pain on palpation.
Diagnosis of Coffin Bone Fractures
Coffin bone fractures are often difficult to diagnose. Since there is no obvious signs of a fracture (swelling or pain on palpation), and lameness varies depending on the portion of the bone that's fractures. The only way to diagnose a coffin bone fracture is with radiography. However, since the hoof wall restricts separation of the fracture pieces, the fracture may not show up in radiographs until a couple days following the injury.