WHAT IS NAVICULAR DISEASE? I remember well when I was a youngster and one of my mother’s horses was diagnosed by the vet as having Navicular Disease. She was very upset, and understandably so, because in those days it was a sentence to long-term lameness and possibly even meant the horse being put-down. We have come a long way since those days. Our understanding of the disease processes that are going on has increased hugely such that what we formerly thought of as Navicular Disease is now looked at and dealt with in a very different way. We used to define Navicular Disease as any long-standing lameness of a forelimb associated with pain in the back third of the foot that could be abolished by desensitising that area with a specific nerve block. Typically, but not always we could see changes to the navicular bone on x-rays and the pain was invariably attributed to pain associated with that bone. It was then realised that you could get pain and lameness from that part of the horse’s anatomy without finding much pathology in the navicular bone, and it became known as “Navicular Syndrome” – or in other words, it was not known specifically where the pain came from. In fact there are all sorts of other structures and important bits of functional anatomy in the foot and the back of the foot, which we now know can become damaged and diseased and cause pain and lameness. Advances in our knowledge have come about by a combination of good scientific studies such as post mortem investigations of lame horses and huge recent advances in technology such as clearer x-rays, ultrasound scanners, and most importantly MRI. If you look at the diagram of the foot, you will see various structures, and to put it basically, any of these alone, or sometimes in combinations can cause pain, and therefore, lameness. So the list of conditions that 30 years ago all came under the umbrella of Navicular Disease now looks something like this: 1. Disease of the navicular bone and its associated structures which include: Collateral sesamoidean ligament injury. Impar ligament injury Navicular bursa disease. 2. Injury to the Deep Digital Flexor Tendon (DDFT). 3. Inflammation and osteoarthritis of the Coffin Joint. 4. Injury of the collateral ligaments of the Coffin Joint. 5. Heel pain due to poor foot conformation and collapsed heels. So you can see that although historically considered to be a single disease, there are a number of different reasons for pain arising in the navicular area. Therefore, it is not surprising that it presents in different ways. For example the lameness can be an insidious, slowly progressive bilateral forelimb lameness, or an acute onset severe lameness of one leg. Some have obvious changes on x-rays, others have none. Sometimes lameness becomes apparent in young horses just starting work, whereas more typically lameness is seen in mature riding horses. It is also seen in horses with vastly different foot shapes. It is a common condition in Quarter Horses, which have narrow, upright, boxy feet, small relative to their body size, as well as in European Warmblood horses, which have relatively tall narrow feet. It is also common in Thorouugbred horses, which frequently have rather flat feet with low collapsed heels. Evidence has recently been presented that suggests that there is a heritable tendency to navicular disease in Dutch and Hanoverian Warmblood horses. DIAGNOSIS Finding that the cause of lameness is from the horse’s foot is relatively easy, but precisely determining which bit of the anatomy it is emanating from and the nature of the injury or disease leading to the pain is extremely difficult, and in many cases still not possible even with today’s knowledge and technology. Having said that, methodical use of nerve blocks, joint and bursa blocks, x-rays, and, in particular, MRI, we are able in many cases to come to a precise diagnosis. With a precise diagnosis, we are able to give a more accurate prognosis for the future of the horse and prescribe more specific treatments. However, horse owners must appreciate that this is not achieved simply by looking at the horse at a short consultation. We are simply not that clever! These cases need careful working-up with costly diagnostic procedures and quite possibly referral to Orthopaedic Specialist and MRI scans. TREATMENT By improving our understanding of the causes of Navicuar Disease and the associated syndromes, we are able to prescribe more targeted treatments. However, I think it is fair to say that there have been few major advances in new therapeutics because most of the conditions are due to injury or “wear and tear”. There are various pharmaceuticals being developed and tried that might in the future be shown to be useful. I do believe that we have become much better at managing these lamenesses, be that rest and gradated exercise programmes for DDFT strains, medication of the coffin joint or navicular bursa, or perhaps most importantly, recognising abnormal foot shape and correcting it with remedial farriery. The importance of foot shape has long been recognised as a possible risk factor in the development of navicular disease. Biomechanics is the study of forces and movement of specific structures of the limb at different and is a fascinating area of current research. The shape of the foot and how it lands on the ground determines many of the stresses involved in the whole limb and has to be crucial to the development of many lamenesses. It is far too simplistic to say that you can prevent navicular disease by having good foot shape and conversely it is too simple to say that navicular disease is due to poor foot shape, but most vets would consider it highly important, which leads me on to another subject…. ... Read Mike's next article on foot shape, coming soon. If you have experienced a horse with Navicular Disease and can offer any helpful advice which you would like to share with other readers, please email us at enquiries@manedealer.com