|
I suspect that no single bone on earth has ever been blamed for so many ills when it has been in fact innocent of almost all charges laid than the navicular bone. Things were pretty simple up until about 15 years ago. If your horse became sore in the foot, developed a short stilty gait, blocked sound to anesthesia of the foot, then you were pretty safe in declaring that your horse had "navicular". If you took x-rays of the navicular bone and you could see evidence of enlarged or irregular so called "navicular vascular channels" then you really had confirmation of the disease. The fate and lives of horses on clinical examination, purchase exams, yearling sales etc. hung in the balance based on the navicular bone radiographic appearance.
Well, guess what. We now know - and this information has been more and more accepted over the last 15 years - that there is virtually no correlation between the appearance of a navicular bone on x-ray and the relationship with clinical problems. In other words, you can easily have the worst looking navicular bone x-rays on earth and a completely sound horse. Conversely, many horses having the classical signs of navicular disease have perfectly "normal" radiographs. The old terminology of declaring the horse having "navicular changes" has been virtually thrown out the window. If you think about it, how do we know if anything has changed if we don't know what a particular horses navicular bone looked like in the beginning? The point is that what we used to call changes was probably normal for that horse.
Now what we do know, thanks in a large part to the advent of the MRI (Magnetic Resonance Imaging) technology at the WSU Veterinary college in Pullman, Washington, is that almost all of the heel pain formerly attributed to the navicular bone is in fact coming from soft tissue injury within the foot. Drs. Bob Schneider and Claude Ragle along with the great team of radiologists at WSU have clearly demonstrated that the small ligaments, tendon insertions, bursae and joint capsule within the foot can clearly be injured in a manner no different than what we might see with a bowed tendon (tendonitis) or suspensor ligament (desmitis).
Only a few of several hundred cases now examined have shown any pathology of the actual navicular bone itself and those were due to bone inflammation, possibly from concussion and not related to the overall appearance of the navicular bone itself as show on radiographs. The classical navicular type lameness is coming from soft tissue injury in the foot.
So this begs the question - should we be taking all sorts of views of the navicular bone when doing a lameness work up or as part of a purchase exam? Well, in my hands, on a purchase exam the navicular views have long since fallen to the level of least priority. Unfortunately some veterinarians and their clients still want to hang their hats and often the sale of the horse on the appearance of this bone. Now don't misinterpret my comments to mean that the navicular bone is of no importance and never has a thing go wrong with it. It can in fact be fractured, it can develop cystic lesions, it can be missing altogether and it can show evidence of spurring or calcification on its edges. These findings, however, are usually a completely separate entity to the typical signs observed with our classical idea of navicular disease. In fact, this term should disappear from our vocabulary and be replaced by something more meaningful like "sore heels!" Sore heels can be due to a multitude of soft tissue injuries as mentioned earlier. These can be caused by outright injury but also by predisposing causes such as poor foot conformation, small feet, long toe, low heel, poor foot balance etc.
So one might ask, is the trip to Pullman and the cost for the MRI (about $1,000) really worth it? The answer is, in most cases, yes. If you can get an accurate etiological diagnosis, then one can accurately begin the rehab process and base your expectations for recovery on factual information. Out biggest problem in advising clients as to the proper protocol for treating and recovering a sore heeled horse is our lack of a definitive diagnosis in the first place. In almost all instances a course of prolonged rest, slow return to exercise and often expert farrier attention is required. The good news is that once we get past the concept that the bone is the problem, then we are more willing to rest the horse appropriately and be more patient in our expectations. The old adage of "bute them and go" just doesn't hold true anymore. Having said that, not all horses are going to recover from "heel pain". Many have as severe a damage to the soft tissue in the foot as we might see in an upper limb tendon or suspensory ligament. We all know that horses with injured tendons and suspensory ligaments don't all return to full performance.
So my parting message is that when your horse is diagnosed as having sore heels, keep an open mind as to the multitude of possible sources of this type of lameness. There are very few veterinarians who can actually see inside a horse's foot with their eyes and accurately tell you what is going on. Radiographs of the foot will continue to be an important part of our diagnostic work up. However, it can only tell us part of the story. We are lucky to have access to the expertise at WSU and the leading edge technology of the MRI.
|