A Navicular Story
People throw the term “Navicular” around an awful lot. Few people understand exactly what it is, how it happens or what it entails. Basically, there are two “naviculars”. There is “Navicular Syndrome” where the heels are contracted and the horse exhibits signs of Navicular lameness: showing lameness while turning or reluctant to cross one front leg in front of the other while turning. The more advanced of this is “Navicular Disease” which can only be diagnosed through radiographs. In this case, the Navicular bone has deteriorated causing bone spurs which aggravate the flexor tendon as it tries to slide over the bone while flexing the hoof.
I’m not the expert on this and there is plenty of more detailed (and accurate) information out there, but I am pretty good at simplifying things. The flexor tendon runs down the back of the leg and attaches to the bottom of the coffin or pedal bone. When the muscle above pulls on this tendon it causes the hoof to lift the heel and go up on its toe and enables forward motion for the leg. As the flexor tendon curves around the heel the Navicular bone acts as a type of floating fulcrum to help it make the turn. In front of the Navicular bone is a gel filled bursa which helps it float and absorb shock. The Flexor tendon is a wide flat strap when healthy.
So, what happens when the hoof gets contracted is that wide flat flexor tendon is squeezed into a narrower rounded shape. This puts more pressure on the Navicular bone and causes more pressure inside the hoof. The contracted heels restrict blood flow causing the Navicular bone to deteriorate causing spurs which tear at the flexor tendon as it tries to slide past to the coffin bone.
Navicular of any kind generally isn’t generally seen in wild horses. Their frogs are on the ground and their heels are spread and stay that way. Improper horseshoeing can restrict the hoof and cause the heels to become contracted. This often happens with gaming horses, reining and cutting for example, where the horseshoes are fitted close so they aren’t stepped on and pulled off during activities. I heard from a Reining breeder and trainer that young horses shod this was are unable to compete much past 5 years old. Horses left untrimmed and in confined spaces can grow long hooves that can get contracted, particularly with upright shouldered horses. Horses coming down toe first for whatever reason will grow a longer heel and can become contracted.
These photos show the contracted hoof on the left and the more normal hoof on the right. The right one also has a coating of Hoof Armor (which has nothing to do with Navicular, except that it doesn’t restrict the hoof) making it look shiny.
My experience has been that Navicular Syndrome can be reversed by removing the horseshoes or cause of toe landing and, with proper trimming emphasizing the heels and frog, allowing the heels to expand. Navicular Disease, where there is bone deterioration, can’t be reversed.