What is Navicular?
Navicular disease, navicular syndrome, caudal foot pain, heel or caudal heel pain. The flurry of names used to define a navicular horse can be downright confusing. It also dosent help that vets, farriers, trimmers, trainers and the like have no real standard for these terms and designate their own meanings to each.
Let’s start with a very generic definition of what any of these phrases mean: Pain the back part of the hoof. Alright, so not so intimidating anymore.
Now let’s dissect that. Pain in the back part of the hoof can be caused by a number of things. Thrush, especially central sulcus thrush, underdeveloped digital cushion, bruising of the frog or digital cushion, crushed heels, foreign object, soft tissue damage or bone damage.
Any number of these can cause pain in the back part of the foot. So what is navicular and what’s not?
Navicular Disease vs Navicular Syndrome
The easiest place to start is to understand these two diagnoses. • Horses with Navicular disease do have bone damage to their navicular bone. • Horses with Navicular Syndrome do not have bone damage to their navicular bone.
We could easily say a horse with a chronic central sulcus infection is a horse with Navicular Syndrome or caudal heel pain or caudal hoof pain BUT not Navicular Disease. Obviously, a vet would have to use xrays to confirm or deny bone damage and Navicular Disease.
This is precisely where the issue lies. I define Navicular Syndrome as a soft tissue injury ie the deep digital flexor tendon. Where as caudal foot/heel pain are injuries to the frog, heels or digital cushion, which do not include bone damage or tendon damage.
Caudal heel pain or heel pain or caudal foot pain are all one in the same with Navicular syndrome. There is pain in the back part of the hoof but no navicular bone damage is present.
Personally, I would like to see a definition of Navicular Syndrome as verified damaged to the soft tissues (mainly the deep digital flexor tendon) via the use of ultrasound or CT scans and perhaps changes to the tip of the coffin bone and elongated hoof shape. Which brings us to the next conundrum about Navicular Disease and Navicular syndrome.
The chicken and the egg
Dr. James Rooney dedicated his professional life to finding out what causes Navicular Disease. For a very long time it was thought that damage to the Navicular bone (caused mainly by a degenerative bone disease, age or genetics) caused damage to the deep digital flexor tendon causing Navicular disease. Makes sense, a rough bone with jagged points and holes would damage a soft pliable tendon in no time. Shredding it with more each step the horse took.
But when Rooney started looking he kept finding Navicular Disease horses with zero bone damage! Once or twice maybe just a fluke but repeatedly? Something about our theory was wrong and he marked his place in history finding out that it’s actually the opposite.
Soft tissue damage ie the deep digital flexor tendon, was actually causing bone damage.
He ran cadaver hooves though toe first landings and through heel first landings on a machine and compared the two. He found no damage to the DDFT or Navicular bone on any hooves that landed heel first. Amazingly he found soft tissue damage to the hooves that landed toe first. On all of them. And when the test was extended, viola! bone damage started, confirming his theory.
He noted the bone looked yellow and discolored where it made contact with the DDFT. So what caused that? Heat. Heat from the friction of the DDFT slamming and stretching against the Navicular bone in an unnatural biomechanical way: toe first!
Caudal foot pain is a serious condition that shouldn’t be minimized whatever the cause. Toe first landings are the first step to Navicular Disease.