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The bones in the hoof are not immune to fracturing. In fact, said Dr. Bob Jones of Uncas Veterinary Clinic in Sherwood Park, Alberta, fractures below the fetlock are quite common. Although foot fractures aren’t an automatic death sentence for horses as many people believe, they are still complicated to heal, require a lengthy, costly convalescence and offer no certain outcome. The hoof fully contains two bones – the coffin bone (also known as the pedal bone, P3 or distal phalanx) and the navicular bone (distal sesamoid bone). The coffin bone is the foundation of the horse’s foot. It is weight-bearing, and provides strength and stability. It is attached to the hoof wall and is the approximate shape of the hoof.
The smaller navicular bone is located deep within the hoof behind the coffin bone. It acts as a support for the deep flexor tendon that extends the length of the leg, passes underneath the navicular bone and attaches to the bottom of the coffin bone. When the coffin joint flexes, the deep flexor tendon glides over the navicular bone.
The lower part of the short pastern bone (P2 or middle phalanx) is located only partly within the hoof capsule. It is attached to the coffin bone by the coffin joint.
Types of Fractures
Bones, no matter where they’re located, can break in a number of ways:
- Simple: bone breaks in two
- Open/Compound: a bone or piece of bone protrudes through the skin
- Comminuted: bone breaks in multiple pieces
- Incomplete: crack in the bone
- Stress: small incomplete fractures
- Chip: small bone fragment
- Avulsion: bone is pulled off when tendon or ligament is pulled
- Displaced: bone fragments have separated and there is a gap; non-displaced, the bones are in their normal positions and only a crack is visible
Coffin and navicular bone fractures are usually caused by sudden traumatic injury such as kicking a hard object, landing awkwardly, working under repeated force (i.e. on hard ground) and, less likely, when a nail or sharp object penetrates the hoof. Degeneration can also leave these bones, particularly the navicular bone, which can develop cysts from that disease, vulnerable to breaks.
Diagnosing the Bone Break
Fractures generally result in an acute (sudden and severe) lameness. If the coffin bone’s outer “wings” are affected, symptoms may not be as pronounced. There may be an increased digital pulse, swelling and heat in the hoof wall. Response to hoof testers when they’re applied over the sole will be positive.
A short pastern break won’t be positive to hoof testers though, as the bone isn’t located directly in the hoof, explained Jones. Fractures in this bone are usually caused by a torqueing-movement or a misstep, and even poor hoof care. They are often seen in reining horses that are asked to perform sliding stops.
If a fracture is suspected, a veterinarian should be consulted immediately. The veterinarian will want to know the horse’s history, such as his general level of soundness, what he was doing when he came up lame and whether a sound such as a crack or pop could be heard. A physical exam might include nerve blocks to determine if the foot is, in fact, the origin of the pain.
A quick diagnosis can be difficult to reach because symptoms are similar to other conditions, namely hoof abscesses. Horse owners can actually take heart, said Jones, because 90 per cent of the time severe lameness (in the horse world, often termed “three-legged lameness”) is related to an abscess, not a break. For this reason, he often suggests horse owners wait it out a little; put the horse in a stall or small paddock for a few days to gauge the horse’s discomfort. “Particularly with coffin bone or navicular fractures, if you just leave them with stall rest, they sort of get better,” he said. “They certainly don’t get any worse, as long as the horse is just standing there or just barely moving around. As long as the bone is not moving and crackling, it doesn’t hurt too badly. They’re usually not going crazy with pain. But an abscess generally gets worse every day until they’re laying down wishing they were dying.”
Jones said he usually waits 10 days to two weeks to perform x-rays anyway because if the bone doesn’t separate, breaks can initially be hard to see on the film. “A negative x-ray of an acutely lame horse that’s not bearing much weight doesn’t mean there isn’t a break there, it just means you didn’t see it,” he said.
And, although he admits it isn’t exactly pleasant watching a horse in pain, Jones suggests owners can’t “get crazy with the painkillers” while waiting for a diagnosis for a couple of reasons. With an abscess, you want to know if they’re getting worse and, if it is a break, a horse who is not feeling discomfort can cause further damage to a broken bone.
During that waiting period, if the problem is indeed a break, calcium is absorbed away from the fracture site as the bone heals and the fracture line gets bigger, making it noticeable on an x-ray. “After a week or 10 days, boom, there it is. And you haven’t really lost anything as far as time goes,” said Jones, who explained that, early on, there isn’t much that can be done for a coffin or navicular bone fracture. Plus, as he noted, the foot bones are already in a natural cast – the hoof capsule – which keeps the fracture relatively immobilized.
The small pastern bone, however, is a different story, he said. “Because it may be just cracked and moving around, it could explode and break apart, so [the veterinarian] really wants to, with a physical exam, locate it pretty well.”
Nuclear scintigraphy, often referred to as a bone scan, can also be used for diagnosis. It is far more sensitive than x-ray and can detect subtle hairline cracks. It is, however, much more expensive and must be performed in an equipped veterinary clinic or referral centre.
Unlike humans who can rest in bed or use crutches, horses are heavy, are hard-wired to keep moving, and must always put weight on their legs. When a horse bears weight, the coffin bone moves as the hoof wall expands. When a fracture is present, the foot will need to be immobilized to prevent that movement and that might mean any one or more of a number of treatment options.
No matter what course of treatment is required, said Jones “you’re looking at between four to 12 months of rehab and turnout.”
Horse owners have a lot to consider when faced with a broken hoof bone. How much money, time and resources do they have to devote to treatment and recovery? Will the horse even be able to handle a long lay-up? Plus there’s no guarantee he will be sound or useful at the end of that long road.
Jones suggests, as difficult as it may be when your horse is hurt, not to make any decisions while you’re under stress. “Fractures are generally not emergencies,” he said. “You’ve got time to figure this out. Have a good think about it.”
For most navicular and coffin bone breaks, if the bone hasn’t separated, immobilization can be achieved by applying a bar shoe (a shoe with metal across its width at the heels) with quarter and side clips around the foot. This prevents pressure on the frog and minimizes hoof expansion. A rim shoe is another popular choice, especially in cases where the joint is involved. This shoe surrounds the bottom of the foot and is filled with acrylic all the way around, essentially acting as a hoof cast.
Fibreglass casts can also be used either on the hoof alone, the hoof and pastern or the entire limb below the hock or knee. Casts have to be changed every few weeks or so though, and can cause pressure sores, nor do they allow for effective alignment of the bone as other treatments do.
In some cases, surgery is necessary. If, for example, the coffin bone is cracked right down the centre, a screw across the joint or a combination of screws, plates and even wire, will help bring the two pieces back together. Called internal fixation, the procedure allows a horse to bear full weight after surgery and often means a quicker return to work. Putting screws into the bone can, however, increase the likelihood of infection. Another issue is preventing a horse from struggling and re-injuring his leg as he comes out of anesthesia. Full-body slings are often used to lessen the chance of this happening.
Surgery may also be required when a fracture from a penetrating wound becomes infected after the bone loses its blood supply and dies off, causing the body to identify the fragments as foreign material. Dead pieces of bone then have to be removed.
Another technique other than surgery is the use of external fixation devices for coffin bone fractures. Pins are placed in the bone above the one with the break. The device runs down the leg and is secured to the bottom of the hoof with a metal plate. Again, the horse can put weight on the leg and walk immediately after it is applied.
As for the short pastern, “there are a lot of surgical options,” said Jones. “Commonly, repairing fractures involves fusing the pastern joint [located between the long and short pastern bones] by using plates and/or screws.” Because the pastern is a low-motion joint, responsible for only three to five per cent of leg’s flexion, the horse’s gait will not be altered after fusion in the majority of cases.
Overall, the prognosis depends on the age and overall health of the horse. Usually, the younger and healthier the horse the better. When the fracture involves the wings of the coffin bone, the outlook is quite good. Fractures affecting the coffin joint are more severe and the prognosis is not as favourable for a couple of reasons. Firstly, when the horse bears weight through the coffin joint, the fractured bone will move, meaning it will be harder for the joint cartilage to heal. Recovery time will be longer and, over time, arthritis and, therefore, chronic lameness is probable.
A navicular bone fracture, however, “is almost a retirement or worse,” said Jones. A neuroectomy or cutting the nerves at the heel (also known as de-nerving or nerving), can extend the horse’s usefulness and comfort.
Not only will the recovery be long, if it’s successful at all, but it will probably be rocky. For example, said Jones, “A lot of times, after a year, the horse is looking good and feeling good and you’ve got a contracted foot because he’s been in and out of a cast or a corrective shoe and the foot has shrunk up a little bit. So, the return to function can be iffy.” By healing one problem, you’ve created another. And, he added, with weakened tissue, there is also a chance of re-fracturing.
Horses whose fractures have healed will be slowly reintroduced to exercise through a veterinarian-guided program of hand-walking, progressing to light riding and eventually to more intensive work. With luck, the horse will return to full form or, perhaps, might take on a new, less demanding job.
“It’s not the end of everything,” said Jones. “It’s not, ‘Oh, he’s got a fracture, you’ve got to shoot the horse.’ I still don’t believe people are thinking that. I mean we’ve been repairing them since 1969 and people still think if he’s broken a bone you’ve got to kill him. There are lots of things you can do. I’d 10 times rather have a fracture than a colic, or even a torn ligament. If you control the situation, bones heal very well. It’s not all doom and gloom.”