Article

Lameness diagnosis seemed to be so much easier 25 years ago, as I recall it seemed pretty easy to look a lot smarter than I feel sometimes these days! With the advent of a large array of technological advances in the diagnosis of the source of lameness we have learned that an awful lot of previously held ideas have been proven to be wrong. It is not hard to find a few examples.

We used to believe that if we blocked the 2 nerves that run along the back of the pastern that we were blocking out pain that was emanating from the heel area of the foot. Of course the prime suspect for the source of this lameness was the navicular bone. One too many irregularities of the navicular bone on an x-ray and the horse was labeled as having navicular disease. Well, we now know that blocking these heel nerves not only blocks out the heel area but in fact almost the entire foot. Not only that, we now know that in most instances the radiographic appearance of navicular bone has no correlation whatsoever with lameness. Blocking out foot pain we now know can anesthetize anything from a mild inflammation within the coffin joint, to a chronic injury to where the deep digital flexor tendon attaches onto the bottom of the coffin bone. The treatment and recovery time for these two problems are drastically different. We also know that if you wait more than about 15 minutes after blocking the heel nerves, in some instances, the anesthetic solution can migrate under the skin up the leg and can block out pain up to the level of the fetlock joint. We used to believe that injecting anesthetic solution into the coffin joint would block out only those structures that were within the coffin joint. Well we now know that the anesthetic solution will very rapidly diffuse out of the coffin joint and can anesthetize many of the soft tissues within the foot.

We now know a lot about what we don’t know about flexion tests! Remember what we call the spavin test? Basically when we flexed the hind leg and the horse trotted off with various degrees of lameness, we called that a positive spavin test. We believed that meant the horse had sore hocks. Well guess what, we now know that a sore suspensory ligament can result in a positive hind limb flexion test and mimic a sore hock. We also now know that when we inject some intra-articular medications into a joint that the medication can diffuse out of the joint and in fact be providing anti-inflammatory therapy medication to surrounding soft tissue. This may not seem all bad as long as we get a positive response to the treatment. This however has the potential to cause some serious problems. Take for example injecting hocks for treatment of perceived hock soreness. We now know that medications injected into the hock joint can diffuse out of the joint and medicate the origin of the suspensory ligament. This has the potential to make the horse appear sound resulting in the potential to cause progressive chronic injury to the suspensory ligament and long term lameness.

So what does all this confusion really mean in the real world? Well it means for sure that we need to keep our mind wide open to what we traditionally thought might be the problem could be something dramatically different. It means that we as veterinarians and you as horse owners must be willing to look a little deeper than we used to in order to come up with a true diagnosis. This can often require more than one visit and more than one session to more precisely localize the source of the lameness. We now have available a much wider array of diagnostic tools to help in this task. This can vary from radiographic and ultrasound examination to the use of MRI and nuclear scintigraphy. Now this also does not mean that common sense, good horsemanship along with a good dose of rest and some anti-inflammatory medication won’t go a long way to cure a lot of problems. At the same time we can no longer assume that a simple little nerve block is going to provide us with anything close to a definitive answer to all lameness problems.