Navicular Disease, its history, and the term’s path to obsolescence
The term navicular disease has been in literature for hundreds of years. For a very long time, all heel pain was considered “navicular disease”, implying that the navicular bone was always the issue.
The first mention of "navicular disease" dates back to 1752. The condition was described by J.F.J. de Gueldenstaedt, a Russian veterinary surgeon, who is credited with the earliest recorded observation of navicular disease in horses.
As veterinary science progressed in the 19th century, the disease became more widely studied and better defined, especially with publications like George Fleming's "A Textbook of Operative Veterinary Surgery" in 1873. (The 1884 edition of of this book is available in our online library.)
Today, the term “navicular disease” is no longer considered correct, and the term to refer to this lameness has gone through several changes in recent years. Firstly, the term “disease” was deemed inappropriate. This led to navicular disease becoming “navicular syndrome”. Recently, the term was changed again.
Podotrochlear Syndrome
With the advent of MRIs, studies conducted on “navicular” horses showed that only 8.8% of the horses actually had damage to the navicular bone itself.
The remaining 91.2% of horses had complex issues involving a system called the podotrochlear apparatus (PTA).
What does it mean?
“Podo” means “foot”, and “Trochlea” means “an anatomical structure that resembles a pulley”.
While the navicular bone is the pulley, many other structures are involved in the functioning of the podotrochlear apparatus.
Chronic lameness of the podotrochlear apparatus is called Podotrochliosis.
One again “podo” means “foot”, “trochli” refers to the aforementioned pulley system, and “osis” means “disease or “condition of”.
Podotrochliosis “the disease or condition of the PTA”, and it is the most up-to-date term to define what we used to call “navicular disease”.
What makes up the PTA
The Podotrochlear Apparatus (PTA) consists of:
the navicular bone
the navicular bursa (a fluid-filled sack that lies between the navicular bone and the Deep Digital Flexor Tendon.)
the distal navicular ligament, sometimes called the “impar ligament”, that attaches the navicular bone to the coffin bone.
The suspensory ligament of the navicular bone, sometimes called the “collateral ligaments of the navicular bone”. It connects the navicular bone to the short pastern bone, and the lateral and medial branches attach to the bottom (distal) of the long pastern bone.
The deep digital flexor tendon (DDFT) as it passes under the bursa and navicular bone.
The coffin joint, called the “distal interphalangeal joint”.
Not only can one or more of these structures become injured, but studies are showing adhesions on these structures.
An adhesion is a band of scar tissue that joins two internal body surfaces that are not usually connected.
Adhesions and damage to one or more of these structures creates heel pain and all the clinical signs of, what we used to call navicular disease.
Symptoms of Podotrochliosis
Your hoof care professional will see a narrowing or contraction of the heels.
The horse will develop a short stride and choppy gait over a period of time.
There will be a toe-first landing, which will increase the incidence of stumbling.
The horse develops problems going straight downhill.
Gait changes when trotting in circles, particularly the inside leg on hard surfaces.
Diagnosis
Radiographs (X-rays) are important to look at bones and their potential changes, however, researchers consistently find the same evidence of radiographic changes in both lame horses and sound horses.
Because a significant portion of the PTA is made up of soft tissues, many problems may be missed in radiographs.
The Gold standard for examining the Podotrochlear Apparatus is an MRI.
It is the MRI that has shown us the multitude of soft tissue damage that can occur in the PTA, but while they are the gold standard, it is difficult for many to find a veterinary clinic that has the necessary equipment to perform them, and the cost of MRIs is above what the average horse owner can afford.
Risk Factors
Overweight and obese horses experience more stress on feet and tendons, particularly when ridden on hard surfaces. The deep digital flexor tendon must bring the animal's weight onto the toe, dramatically increasing the pull on the navicular bone.
Feet that are too small for the horse’s body from a conformation standpoint may be characterized by a small navicular bone that will be subjected to excessive forces.
Long toes, low heels: the longer the toe, the more stress is placed on the podotrochlear apparatus for beak-over.
Feet that go more than eight weeks without professional hoof care: the longer the toe, the more stress is placed on the podotrochlear apparatus for beak-over.
Horses kept in stalls for long periods of time will have reduced blood supply to the navicular bone.
Because of the complexity of the condition, podotrochliosis is, and will continue to be, a problematic lameness to treat for owners, farriers, and veterinarians alike.
However, with increasing breakthroughs in imaging and new medical treatment, the prognosis for affected horses is improving.
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