Navicular disease once was called 'the last resort of the diagnostically destitute (practitioner),' based on the syndrome's ambiguous symptoms and the practitioner's inability to isolate definitely the source of the horse's pain. In the 1980s, navicular disease was believed to be the most over-diagnosed lameness in American horses. The reason? You could never really be sure what was causing the lameness. Symptoms were lumped together; owners demanded a name to put on the lameness.
That was all before the renaissance in foot studies, which has given us the ability to experiment with shoeing, nutrition, joint injection, and pain medication to give the horse a path out of the pain. Most people point toward better quality machine-made shoes--with longer heels, wider webs, and better overall support--as being the single largest contributor to the increase in soundness in our horses. To that, I'd add the availability of many more highly skilled farriers at work on our horses. They are providing improved hoof balance and remedying those acute toe angles that place the navicular bone in an ouchier-than-need-be position in the foot.
For the purposes of this column, let's refer to the problem as ï¿½navicular lameness,ï¿½ meaning that the horse shows signs of lameness in the caudal (back) part of the foot when hoof testers are applied. Diagnostic nerve blocks also can isolate the source of pain to the back of the foot.
That is still pretty vague; navicular disease has many different definitions, depending on to whom you talk, and on what day. Technically, what we are looking for in these cases is podotrochleosis, a specific aspect of ï¿½navicular diseaseï¿½ centered in the area of the tendon/bursa/bone sandwich at the point where the deep flexor tendon curves to its point of attachment at the base of the coffin (P3) bone.
In Germany, where navicular disease in warmblood horses has been extensively studied, the syndrome is broken down into several specific disorders, one of which is podotrochleosis. Fortunately for us, some of the German texts now are being translated into English and international conferences offer simultaneous translation so we can more easily follow the work of Austrian, Swiss, German, and French researchers.
Clinical research has shown that some horses might exhibit radiographic signs of navicular problems (i.e., deterioration of one or more surfaces of the tiny navicular bone, or a lesion in the bone itself), but have no pain. Other horses are in obvious pain, but have no radiographic signs of damage. Some horses respond to changes in hoof trimming or shoeing; others do not. Some horses seem to recover after being diagnosed as absolutely, positively suffering from irreversible navicular disease, which would indicate that the horse wasn't truly suffering from that problem at all. Other horses deteriorate with time, or the lameness is intermittent, without coordinating signs appearing on radiographs.
Traditionally, the upright, boxy foot of the Quarter Horse has been the traditional favorite campsite of navicular ills. I, for one, can attest to a sense of panic the first time I had an Arabian horse in my care. He went lame. For the first time, I really looked at his feet, and I was sure that both he and I were doomed. After a lifetime of looking at round, sloping Thoroughbred feet, I was sure that I was looking at a textbook case of navicular disease. What would I tell his owner? What had I done wrong? I just didn't realize that there are horses built that way--in fact, more horses than not! Of course, the horse recovered, but ever since then I have watched how horses land over fences, depending on whether the horses have sloping pasterns, or upright ones. Try it. It will make a horse show go faster if you're a spectator!
New diagnostic media and technologies from other fields of equine veterinary care slowly are being applied to the coffin joint and navicular bone. The goal is to help equine practitioners ascertain where damage might be present in the navicular area, and to evaluate whether or not therapy will be useful in keeping the horse sound, or returning a severely lame horse to an athletic career. Scintigraphy is an example of one medium that shows great promise. Many veterinary hospitals have made substantial capital investments in nuclear scanning devices and storage facilities. Magnetic resonance imaging (MRI) makes it possible for a surgeon to see the soft tissue in a foot before deciding on a surgical procedure.
The impetus behind the use of this equipment is, of course, the horse owner's urgency to know the exact extent of damage, and his or her desire for a definitive prognosis: ï¿½When can I ride him again? Will he be fit for the finals? Will he ever jump again?ï¿½ Before technology entered our game, horses were given a month-long (or longer) dose of ï¿½Dr. Greenï¿½ (turnout, lay-up) and returned to training when and if they exhibited soundness. If Dr. Green didn't work, the horses soon showed up in the classified ads.
But, sometimes a great step forward can come by using an old tool in a new way. At the University of Minnesota's College of Veterinary Medicine in St. Paul, Tracy Turner, DVM, has taken a new approach to diagnosing navicular disease in a more precise manner. Surprisingly, his new procedure sounds high-tech, but it is relatively ï¿½low-tech,ï¿½ and can be applied by most equine practitioners in the field at a reasonable cost to the owner!
First introduced at the 1997 annual meeting of the Association for Equine Sports Medicine and discussed at the 1998 Bluegrass Laminitis Symposium, Turner's procedure is called ï¿½navicular bursography.ï¿½ It isolates one of the foot's most vulnerable structures, the navicular bursa, and allows the practitioner to evaluate the condition of the bursa and identify it as a possible cause of the horse's problem.
What Is The Navicular Bursa?
Inside every foot is the all-important coffin joint, the intersection of the short pastern bone (P2), coffin bone (P3), and navicular bone. The coffin joint flexes with each step the horse takes, and is stabilized and manipulated by the extensor tendon, which attaches at the front of P3, and the deep digital flexor tendon, which attaches on the ground surface of P3.
The navicular bone sits at the back of the joint and serves as a fulcrum over which the deep digital flexor tendon glides on its way to its point of attachment on the bottom of P3.
Navicular bones are subject to many different problems, but one area that seems particularly susceptible to injury and degeneration is a tiny fluid-filled sac called the navicular bursa. The bursa is a pillow-like sac of lubricant that cushions the bone and tendon. Its most basic job is to fill a space, and keep the structures on either side of it moving smoothly.
Much of what we know about the navicular bursa has come to us not by studying navicular lameness directly, but by seeing catastrophic injury to the horse's foot when a puncture wound, such as a nail or spike, penetrates the back part of the foot and damages the bursa, allowing infection to set in. The horse suddenly is in great pain and unable to flex the tendon in the normal way. Surgeons developed what is called a ï¿½street nail operationï¿½ to open the bursa; a window is cut in the frog and the bursa is drained of septic tissue. Many horses never regain soundness after such an injury to the bursa.
If a puncture wound can cause that much of an impact to a soft tissue in the horse's foot, it must be an important structure. Still, until recently, researchers and practitioners alike chose to argue over the bone degeneration vs. loss of blood supply schools of navicular lameness etiology. Only in the past ten years, with the work of pathologists like Roy Pool, PhD, and James Rooney, DVM, has the bone taken a backseat to the other structures in and around the joint.
One of the more recent changes in the overall care of our lame horses is the increase in neurectomies being performed. This controversial surgery is a last resort for some horses, many of whom have undergone other surgeries and a long list of therapies and corrective shoeing. While neurectomy is always a last resort, many veterinarians were performing them in the belief that a problem in the bursa or tendon must be causing the horse prolonged pain. Using a diagnostic tool that can isolate those structures and show irreparable damage makes a neurectomy a little easier for practitioners and owners alike.
A leaky or ï¿½stickyï¿½ navicular bursa can be isolated by any veterinarian in most settings where a sterile procedure can be followed. The idea, in a nutshell, is to insert a needle between the bulbs of the heels and into the bursa. This sounds easy, but one could easily miss the bursa altogether, unless good lateral (side view) radiographs have been taken to identify the angle of the joint and the location of the bone. Once the needle is in place, additional lateral radiographs are taken to verify that the needle is being positioned correctly. When the veterinarian feels that the needle is in the bursa, ï¿½contrast mediumï¿½ (radio-opaque dye) is injected through the needle.
An alternate procedure used by Turner is to flex the leg, holding the foot off the ground. The radiograph taken is referred to by veterinarians as the ï¿½PP-PD obliqueï¿½ (palmaroproximal-palmarodistal caudal tangential). The resulting radiography shows the dye-filled bursa as a thin line following the contour of the navicular bone; any irregularities are obvious.
Turner and others around the world have been experimenting with this type of low-tech imaging of the bursae to help horse owners who might not be able to afford expensive nuclear medicine workups, but still want a definitive answer as to why their horses are lame. One problem with the procedure is that if the bursa or tendon is damaged, the resulting scar tissue might make it difficult to insert the needle!
Turner used this technique in a study of 97 horses, all of which exhibited pain in the caudal (back) part of their feet, suggesting some sort of discomfort in the navicular zone. When all the ï¿½burso-gramsï¿½ (as they became known) were completed, Turner was able to divide the radiographs into five sets. One set showed a nice, even band between the tendon and navicular bone; the second set showed thinning or even erosions in the bursa; the third set showed diffusion of the dye, indicating that it had perhaps been absorbed into tendon adhesion areas; a fourth set showed bone cysts taking up the contrast material; and a fifth set showed deterioration in the tendon where it met the bursa. Horses in the last three groups found increased comfort from anesthesia being injected into the bursa. Horses in the first two groups were just as lame with anesthetic in their bursae.
Bursography doesn't make any quantum leaps toward a ï¿½quick fixï¿½ for navicular lameness in the horse, but it might help some horses avoid unnecessary neurectomies and spare some owners the expense of extended therapy for horses that are not able to heal.
The Big Picture
The best treatment for a horse with navicular lameness is to avoid the cause of lameness in the first place. That begins and ends with the best possible hoof care you can provide for your horse, on a regular schedule, with a qualified farrier. Work horses on good surfaces, warm them up, cool them down, and avoid endlessly repetitive movements or repeated high-impact activities like trotting on pavement, imbalanced riders, and messy landings from jumps.
Still, some horses seem to be predisposed to navicular lameness. Keep an eye out for subtle signs that the horse is uncomfortable and know his limitations. Keep radiographs on hand for comparison, and get to know your veterinarian. The two of you will be spending lots of time together trying to keep that horse sound. It takes a genuine commitment from an owner to keep nursing along an unsound (however brilliant) performance horse.
When and if you decide to give up on a horse suffering from navicular lameness, be honest with prospective buyers about what you have done to keep the horse sound to that point. Remember that an uncomfortable horse has many ways of using its body to compensate for pain. A borderline horse which suddenly changes riders, tack, farriers, and environment might have a serious setback, or lameness could flare up in another part of the foot, leg, or back as the horse attempts to avoid striding a certain way.
Horses with navicular lameness might not jump as high, might not have any extension to their trot, and they might be has-beens at the horse show, but there are thousands of them out there, living productive lives and giving people great enjoyment. Work with your veterinarian and your farrier and someone who fits tack to help you make your horse as comfortable as possible. Your horse might be one of the lucky ones.
Dr. Turner's paper on navicular bursography will be published in full in the proceedings of the 1998 Bluegrass Laminitis Symposium.
Other books and reading:
Veterinary Clinics of North America April 1989: The Equine Foot: Pathophysiology of Navicular Syndrome by Pool, Meagher, and Stover;
(ibid): Diagnosis and Treatment of the Navicular Syndrome in Horses by Tracy Turner
Concise Guide to Navicular Syndrome in the Horse by David Ramey
The Lame Horse (revised 1998 edition) by James Rooney
Nonselectivity of Local Anesthetics Injected into the Distal Interphalangeal Joint and the Navicular Bursa by Robert Bowker in Proceedings of the 41st AAEP convention.
Comparison of Responses to Analgesia of the Navicular Bursa and Intra-Articular Analgesia of the Distal Interphalangeal Joint in 102 Horses by Sue Dyson in Proceedings of the 41st AAEP convention.
International Symposium on Podotro-chleosis in Germany in Hoofcare & Lameness Issue 1, 1994.
Equine Joint Mechanics: An AAEP/H&L Report by Roy Pool, Hoofcare & Lameness Issue 66.
Navicular Disease (Podotrochleosis) in Color Atlas of the Horse's Foot by Chris Pollitt (bursography illustrated in photos).
Foot Ailments in the Coffin Joint, Distal Sesamoid Bone, and Podotrochlea by Hertsch et al in The Hoof (English edition, 1997).
About the Author
Fran Jurga is the publisher of Hoofcare & Lameness, The Journal of Equine Foot Science, based in Gloucester, Mass., and Hoofcare Online, an electronic newsletter accessible at www.hoofcare.com. Her work also includes promoting lameness-related research and information for practical use by farriers, veterinarians, and horse owners. Jurga authored Understanding The Equine Foot, published by Eclipse Press and available at www.exclusivelyequine.com or by calling 800/582-5604.