EQUINE VETERINARY SERVICES March 2009 Coffin Bone fractures What is the coffin bone? The third phalanx (P3), pedal bone, or coffin bone, as it is often called, is so named because it lies within the “coffin” of the hoof wall. Fortunately, coffin bone fractures are not always as gloomy as their name suggests. How do fractures happen? Pedal bone fractures are most commonly caused by some sort of trauma to the hoof – usually a kick to a fixed object such as a stable door, knock on a cross country fence, or very strenuous work on hard ground. Other causes include penetrating wounds to the hoof, as well as secondary to infections of the hoof which have spread to the pedal bone (“Pedal osteitis”). These infections weaken the bone and make it more prone to fracture. The majority of pedal bone fractures (80%) occur in the front limbs. How will I know if my horse has a fracture? The horse will normally have an acute, moderate to severe lameness on the affected leg. They will often not even bear any weight on the limb. The lameness may initially be less severe but worsen over the first 24 hours as the soft tissue surrounding the fracture swells inside the hoof wall and places pressure onto the fracture site. If you find your horse in this state be sure to call your vet as soon as possible! There are several other conditions which can present in the same manner as a P3 fracture. These are: Hoof abscesses, sole bruising, penetrating wounds to the sole, laminitis, navicular disease, pedal osteitis, and infections of the coffin joint or navicular bursa. How will we diagnose a fracture? After looking at the horse and assessing the lameness, the hoof should be thoroughly cleaned and examined to rule out any sole bruising or penetrating wounds. There is often an increased pulse in the digital arteries. The vet will then often use the following tools to help make a diagnosis: Hoof testers are used to apply pressure and assess pain in the hoof and underlying pedal bone. Horses with a pedal bone fracture will be sensitive over the ENTIRE hoof. Tapping of the front of the hoof wall may also elicit pain. Nerve blocks involve the injection of a small amount of local anaesthetic under the skin, overlying the nerves supplying the leg and hoof. This numbs the area below the block and helps us to localize the lameness. In the case of a suspected pedal bone fracture, an abaxial sesamoid block performed at the level of the fetlock should result in an improvement of the lameness. Multiple X-rays should be taken of the hoof, and sedation may be needed in order to obtain good quality veiws. Keep in mind that not all early fractures will be visible on x-rays if the fracture fragments are not displaced. If this is the case then it may be necessary to stable rest the horse and re-take x-rays in 10-14 days time when the fracture line will become more visible due to loss of bone around the fracture site. Some fractures not visible on x-ray can be seen using scintigraphy (a “bone scan”). The only scintigraphy machine in South Africa at this stage is at the Onderstepoort Veterinary Academic Hospital in Pretoria. Scintigraphy shows up areas of inflammation (“hotspots”) in the bone. of fractures are there? What types What type of fractures are there? There are several kinds of pedal bone fractures, grouped into 6 types according to their location: Types of Fractures Type 1: Wing Fracture Type 2: Articular Wing Fracture. Type 3: Articular Mid Fracture. Type 4: Extensor process Fracture Type 5: Comminuted Fracture Type 6: Chip Fracture. Type 7: Foal Fractures. What is the treatment? Strict stable rest: Regardless of whether the fracture is being treated surgically or conservatively, stable rest is one of the most important requirements for healing. The horse should be box rested for at least 2-6 months, after which restricted exercise (hand-walking) can gradually be introduced for 3-12 months depending on the severity of the lameness and fracture type. Shoeing: The horse should be shod with a full rim or full bar shoe with toe clips, to limit expansion of the hoof wall during each step and help the hoof to act as a natural cast and stabilize the fracture fragments. Pain control: Pain medication (Eg: Phenylbutazone) should be used in order to control pain and inflammation as well as encourage the horse to bear weight on the affected leg in order to prevent laminitis in the opposite (“good”) leg. Surgery: Fractures through the joint and palmar/plantar process (Type II) or middle of the pedal bone (type III) may require the placement of a screw through the fracture fragments in order to pull them together. This surgery not without complications as the surgery site is prone to infection post surgery. Fractures of the extensor process (Type IV) can be removed via an arthroscopy. Antibiotics: Broad spectrum antibiotics are needed if there is any penetrating wound into or infection of the pedal bone. What is the prognosis? The prognosis varies with the type and site of the fracture. Closed fractures not involving the joint have the most favourable prognosis and are often able to be treated conservatively. Fractures into the joint (“Articular fractures”) carry a poor prognosis due to the high risk of arthritis (DJD) in the coffin joint (often called “low articular ringbone) following the fracture. Fractures caused by penetrating wounds or infection in the pedal bone are also associated with a poorer prognosis as the infection complicates healing of the fracture. When can my horse return to work? The simple answer is: When the horse is sound! Radiographs should be taken before returning the horse to work, however bear in mind that the pedal bone may heal by fibrous tissue only and the fracture line may be visible many years after the horse has become sound and is back in full work. Drs: Dave Mullins, Helen Tiffin, Tanya Hughes, Jenny Lawrence, Anna Bowker.