The cause, anatomy, prevention and treatment of Navicular Disease. Navicular Disease Doug Butler PhD, CJF, FWCF Navicular Disease ©2011 by Doug Butler PhD, CJF, FWCF Butler Professional Farrier School Near Chadron, Nebraska A diagnosis of navicular is feared by all who ride and show performance horses. It’s so scary some people refer to it as the N word! Although it has always been a problem for athletic horses, it seems to be more prevalent today than even a few years ago. Horse owners, farriers, and veterinarians are concerned about its prevention and treatment. What is navicular disease? Navicular disease, often referred to as navicular syndrome, is a broadly defined term describing pain in the navicular bone or associated structures. It is usually thought of as degenerative disease of the navicular bone. Yet, many structures associated with the navicular bone may be involved including: the navicular bursa, the deep flexor tendon, the articular cartilage of the navicular bone, the impar or distal navicular ligament, the collateral ligaments of the navicular bone (also called the suspensory ligament of the navicular bone), and even the coffin joint. The severity of the condition depends upon its cause, its duration, and the type and number of structures involved. Since it is often hard to differentiate the location of the pain, many vets have referred to the condition as palmar heel pain. What structures are involved in an afflicted foot? The navicular bone is located under the center of the frog and digital cushion when looking at the bottom of the foot. It acts as a fulcrum point that gives a greater mechanical advantage to the deep flexor tendon and its muscles. Excessive pressure on the bone causes it to become diseased and remodel. The remodeling causes pain. Most commonly the structures affected in the initial stages are: the navicular bursa, the deep flexor tendon, the navicular ligaments, and the navicular bone. Affected horses will take shorter steps and strides. ©2011 by Doug Butler PhD, CJF, FWCF Page 1 Navicular area of dissected specimen with deep flexor tendon at the bottom; navicular bone and opened navicular bursa with synovial fluid in the middle. There are at least four types of the disease classified by the structures involved. The tendinous type involves the inflammation of the deep flexor tendon and navicular bursa. Inflammation causes pain. The ligamentous type involves a sprain of the ligaments supporting the navicular bone causing a disruption in the blood supply to the bone. The disruption of the circulation (called ischemia) causes pain. The osteo or chondral type involves the navicular bone and articular cartilage that is not thoroughly conditioned and is therefore subject to injury. This causes pain. The navicular bone is part of the coffin joint, and eventually it may become involved. The articular or type involving the joint is painful and the most difficult type to treat. It usually has an unfavorable prognosis (outcome). How can you determine if your horse has the disease? Horses with long toes and low heels are predisposed to navicular. This is a common conformation in many of our modern horses. Neglect of regular hoof maintenance aggravates it. Horses with underrun heels (heels that have a hoof angle at least 5 degrees less than the toe) have an 80% chance of developing navicular disease. They put excess stress on the deep flexor tendon and navicular bursa. Horses with pastern angles greater than the hoof toe angle are also predisposed to the condition. They put excess pressure on the navicular ligaments due to the concussion caused by a straight leg. ©2011 by Doug Butler PhD, CJF, FWCF Page 2 Horses with navicular have a particular gait and stance. They will have a short stride (sometimes called a “pottery” gait), try to shift their weight to the rear legs, and favor the most affected leg until they warm up. Like arthritis or bursitis in people, the condition will be less noticeable immediately after exercise. It is most noticeable when the horse is first moved after being in a stall or tied up for a time. When standing, the most affected foot will be held forward. This is called “pointing.” The most affected pointed foot will nearly always be smaller. Horses with navicular try to prevent stress on their sore heels by landing toe first. When trimming the toe in an effort to align the phalanges and reduce the stress on the navicular bone, the farrier will notice evidence of bruising and tearing in the area of the white line. Also, just above the buttress of the heel the “navicular waist” may be seen. This is evidence that the horse is avoiding loading of the heels causing them to contract. The toes of the shoes will be worn like a rocker toe, so that there is less stress on the tendon. Top: Worn shoe from navicular horse; Bottom: Rocker-toe made by farrier to mimic wear and ease breakover. The skilled use of hoof testers is the most accurate way to determine if a horse is affected by navicular disease. First test other areas of the foot to determine the horse’s reaction to pressure. Their response varies. After you see what is normal, then proceed to exert pressure over the navicular area. Hoof testers, placed across the foot with one jaw over the middle third of the frog, the other on the wall, will usually elicit a response when the bursa or tendon is involved. Hoof testers, placed at the widest part of the hoof about ©2011 by Doug Butler PhD, CJF, FWCF Page 3 ½ inch below the coronary band, will usually illicit a response if the collateral ligaments of the navicular bone are involved. Using hoof testers. Left: testing bursa and tendon over middle third of frog; right: testing collateral ligament on the ends of navicular bone. Navicular bones in various stages of remodeling. Top: normal, left center = “spur” lesion; right center = “lollipop” lesion. Radiographs are also used by veterinarians to diagnose the condition, but are not as valuable as the hoof tester. The great thing about x-rays is that they can identify other possible causes of pain such as fractures and abscesses. The not so great thing is that only about 50% of the time does the pathology of “spur” or “lollipop” lesions on the film correlate with the pain seen in the foot. Some horses are born with defects in the bone. Without a reference radiograph taken some time ago, one cannot accurately say there are navicular bone “changes.” Most navicular disease is in the front legs since they support more weight. Less than 5% develop the disease in hind feet. ©2011 by Doug Butler PhD, CJF, FWCF Page 4 Radiograph of navicular bone showing “lollipop” lesion in center of its distal (bottom) border. Veterinarians can also use nerve blocks, MRIs, or nuclear scintigraphy when available. However these diagnostic tools rarely change the treatment regimen or prognosis of navicular. What causes navicular syndrome? Most horses that get navicular are predisposed to it by heredity. The conformation of horses is highly heritable. Conformations of straight shoulders and pasterns or long sloping pasterns and acute angled hooves with underrun heels are undesirable. However, there is some evidence that the ability to do various athletic events such as racing, roping, cutting, reining, jumping, and dressage is associated with the conformation predisposition to this disease. The disease has been around since ancient times and has even been identified in fossils from prehistoric horses. Keeping horses confined with little regular exercise contributes to its modern day prevalence. Breeding unsound horses perpetuates the disease. What can you do? Many horses have their useful life extended with proper attention to foot and horse management. You must recognize that your horse has a problem that requires constant attention by a competent farrier. A horse with navicular disease is a high maintenance horse. These horses must be frequently reset (usually monthly) to keep the pastern angle and the hoof angle parallel. Although they need a small exercise area, they cannot be turned out in paddocks (especially when muddy) where they might lose their therapeutic shoes. Protective boots should be worn to prevent lost shoes when competing and hauling these horses. Feed a balanced ration, but do not over feed. Horses should be adequately trained and conditioned for the work they are asked to perform. A horse is in ©2011 by Doug Butler PhD, CJF, FWCF Page 5 good condition when its ribs cannot be seen, but can be detected when you draw your hand across its side. The exception is the Thoroughbred and horses with Thoroughbred influence in their pedigree. Their ribs may always be visible, no matter what their condition. Avoid purchasing young horses or breeding stock that have small feet for their body size. Small feet on a large body predispose a horse to the disease. Before you fall in love with the horse you are considering buying, be critical of conformation faults that may predispose the horse to the disease. Extremely upright and extremely sloping pasterns should be discriminated against. Avoid overfeeding young horses. This often produces epiphysitis which in turn often produces abnormal bone growth and a length difference in the legs. More weight carried on one leg for a time due to pain in the opposite limb, may increase the incidence of navicular disease. Train young horses equally in both directions to avoid excessive stress on one leg. Horses that had shown navicular symptoms for less than one year were fed nine grams of Cosequin (condroitin sulfate/glucosamine joint flex nutraceutical) twice a day for 56 days.