By Ellis Traywick, DVM
The word navicular can cause anxiety for horse owners who are facing the possibility of this diagnosis, and if you pre-purchase a horse, you may question how worried you should be about navicular changes on the x-rays. Understanding these key things about navicular syndrome can make it a less confusing subject and help you recognize the early signs.
1. Navicular disease is estimated to be responsible for 1/3 of all chronic lamenesses, the most commonly affected breed being the Quarter Horse. The offending structure can be the navicular bone, the sac of fluid that protects it from the deep digital flexor tendon (bursa), the ligaments that hold the navicular bone in place, or the fibers of the deep digital flexor tendon in that general area.
Photo credit: www.horsejournals.com/horse-care/hoof-care/lameness/treating-navicular-disease-farriery
2. Horses with navicular usually have a history of subtle onset of lameness. The horse may just look stiff early on in the course of disease and stumble frequently. The lameness may seem inconsistent and switch from one (front) leg to another. Putting the horse on a circle or a hard surface can make it worse.
3. The cause is mechanical. Either a normal, healthy navicular region is subject to abnormal loads (examples of which include over or erratic use, hard ground, and even obesity), or an inferiorly conformed navicular region is subjected to a reasonable amount of stress. Both result in abnormal overload. Studies have revealed that the shape of a horse’s navicular bone is an influential conformation factor.
4. After several months of pain and un-weighting of the heels, the feet may even begin to change shape, growing more upright and contracted (smaller) in the heels.
Photo credit: VMRCVM
5. Trimming and shoeing to improve hoof biomechanics is the most important thing and must be ideal in order to get any benefit from adjunctive therapies. A good trim relieves pressure in the navicular area by keeping the toe back and engaging other parts of the hoof capsule (such as the sole and frog) in weight bearing to help the heels.
6. We often do not appreciate a correlation between radiographic results and clinical lameness. Radiographic changes may be absent early on because the overload is just affecting the soft tissues. Normal radiographs do not mean that the horse does not have navicular pain.
7. Navicular disease is degenerative, but it doesn’t have to be a usefulness death sentence. Finding the right shoe can be trial and error. There is not one shoe that’s right for navicular. Also, sometimes problems that look like navicular are actually in the coffin joint.
8. MRI is the gold standard for diagnosing lameness lesions within the foot. Most MRIs of the foot are going to reveal more than one problem, which can be intimidating. Instead of trying to decide which is the most significant, knowing all the problems that are there helps tailor the treatment and shoeing to a plan that will benefit all the problems at the same time and thus achieve the best chance of success.
9. The latest drug approved for navicular is Osphos, which is the same class of drugs as human drugs Boniva or Fosamax. It works by inhibiting bone resorption by binding osteoclasts (bone cells that break down bone tissue), thus reducing bone pain.