Navicular Syndrome has been a problem in many equines for many years, but tends to only show up in the equine athletes in their prime of life. It is something that can cause pain and in some cases it will cause the end of the horses working life. This is because it has a degenerative effect on the soft tissue and Navicular Bone over time (and this can be a short or long time frame). Veterinarians and clinical researchers along with farriers have been trying to unravel the causes for centuries, and still have no real prescription for treating this syndrome. 

In my practices I see a large amount of equine present with this type of syndrome and this is different to a horse that presents with Navicular bone disease.  The first thing I like to do is have x-rays taken to rule out bone disease or bony changes that could be the underlying problem. As Navicular syndrome is not a disease but something that causes pain in the region of the Navicular bone.

Lets us look at the anatomy of this area first to see the relationship of Navicular bone to the surrounding structures, (bone or soft tissue) and how it is suspended in the hoof. The Navicular bone sits at the back and in-between the wings of pedal bone, its job is to act as a fulcrum for the deep digital flexor tendon (DDFT) and maintain tension and location of DDFT. It is held in place by the Impar ligament attaching it to distal phalanx and collaterally by the collateral sesamoidean ligaments attaching it to the proximal phalanx. The anatomy of these structures is very detailed and in recent years researches have a better understanding of the vascular system in this area. But information regarding function and the importance of the ligaments, which attach the Navicular bone to the surrounding bones along with the effects of the orthopaedic stance of the equine is still being understood.

If we look at the physical forces impacting upon the foot and in particular the intersection of the distal phalanx and Navicular bone we can easily hypothesize that excessive forces could cause sufficient trauma to the soft tissue of this region. This ongoing trauma will have an inflammatory processes on the soft tissue and alerter the physical functioning of the foot. These forces lead to the foot having less vascular perfusion in the short term with long term seeing secondary features such as necrotic tissue of the area. This is when we observe clinical changes in the behaviours’ of the equine, such as chances to locomotion and attitude.

Understanding that this area of the foot can be placed under extreme pressure during flight and the integral part it plays in dispensation of energy upon impact with the ground it is not hard to see why a horse would present with such clinical symptoms. 

I have carried out hundreds of hoof resections over the years and my clinical research of this complaint has reviled some consistencies in the soft tissue architecture of the impar ligament / collateral sesamoidean ligament and the deep digital flexor tendon. In a large percentage of my resections of horses with this problem I see pathology or structural changes to these structures. The deep digital flexor tendon first show signs at its distal insertion to distal phalanx with a yellowing to the colour of the tendon body. The texture of the tendon at the insertion point also shows signs of the fibrous break down and I believe both these pathologic changes are due to stress leading to firstly inflammatory processes and secondly diminishing vascular perfusion. The impar ligament presents with similar changes but due to the forces placed upon it is the first structure to manifest problems. It seems to be that in the early stages of the syndrome the impar ligament shows signs of bruising at the proximal insertion point to Navicular bone and then at the distal insertion point to distal phalanx and DDFT. The bruising origan is always in coloration to the orthopaedic balance of the direct corresponding limb. This is to say that if weight if carried to one side of the structure more than the other the soft tissue presents with bruising on the corresponding side. It is when the weight is carried more forward or back on the structure that we see pathologic changes to the insertion point of distal phalanx and more so changes at insertion of DDFT.       

My research has shown that we need to ensure that Navicular bone is in what I call a neutral position; this is when the physical forces placed upon the Navicular bone do not cause the supporting ligament to be pulled one way more then the other. I find having three lateral radiographs one on soft exposure showing the internal structural alignment within the hoof capsule of the foot one on medium exposure to show soft tissue and one on hard exposure to show alignment of Navicular bone with other structures. This is very important to know the interrelationship of Navicular bone to the soft tissue architecture and bony column structure of the limb.

 Having orthopaedic imbalance of the limb will cause the internal misalignment of the soft tissue supporting Navicular bone and causing structural misalignment of Navicular bone to distal a middle phalanx. This then has an inflammatory process on the impar and collateral ligaments and other structures of the foot causing the horse to show systems that the equine industry knows as Navicular Syndrome. My resections have shown this type of imbalance will cause the Navicular bone to sit asymmetrically to distal sesamoid and cause uneven stress on the collateral ligament and DDFT as it runs back and forth over Navicular. This extra tension on Navicular has an inflammatory action on it causing changes to the periosteum and long term cortex of the bone. When this imbalance is left to continue long term we see physical changes to the alignment of the distal bone structures and wearing surfaces of the bones. Resections have revealed remoulding of the distal and proximal surfaces of all phalanx bone and in one case massive change to the distal joint of third metacarpal bone.

In conclusion I would like to say that I view this syndrome as an early warning sign of imbalance in the equine and if not addressed correctly then long term problems will manifest throughout the equine. On a positive point I do have a very good success with returning these horses back to work if we can treat them in the early stages and not left to prolonged stress that will damage the internal soft tissue structures of the internal hoof.