So-called navicular or caudal heel syndrome is one cause of lameness that can appear in horses of any breed or discipline. It can be limited to one limb; however, it most commonly affects both front hooves, causing bilateral lameness. While veterinarians have documented it in the rear feet, these cases are very rare.
"Horse people, in general, tend to lump all heel pain under the 'navicular' umbrella, even though other issues might be to blame—hence the term 'navicular syndrome,'” says Dr. Tracy Turner.
It’s an overly simple name for a complex condition that we now know is most accurately described as podotrochlosis or podotrochleitis, because it can involve more of the podotrochlear apparatus than just the navicular bone, such as the navicular bursa or associated soft-tissue structures (e.g., the deep digital flexor tendon [DDFT] and collateral ligament of the distal interphalangeal joint [DIP or coffin joint]).
“It’s important to make this point because a more specific diagnosis allows for a more specific treatment, and there are lots of different structures that may be injured in the pain syndrome,” he says.
Veterinarians believe navicular is caused by mechanical stress and strain due to the constant pressure between the navicular bone and DDFT, which leads to the degeneration of those and other structures that make up the podotrochlear apparatus. Poor foot conformation, such as a long toe and low heel, increases this stress and might potentiate the development of the condition.
The result is lameness, which can become chronic. “It is characterized by shortness of stride, toe-landing, pain from the center third of the frog,” says Turner.
Early on these horses might present with a shortened stride right out of their stalls or while warming up, says Dr. Duncan Peters. “In more chronic cases, the horse that used to have a longer stride will become choppier and less fluid, because the horse is stabbing the toe to take the pressure off the back of the leg,” he says, describing the syndrome’s progression.
While any horse could develop podotrochlosis, research shows certain breeds, such as Thoroughbreds, Quarter Horses, and Warmbloods, are more at risk, and that it’s most commonly diagnosed in mature horses from 4 to 15 years old. Because of the relationship between hoof angles and the podotrochlear apparatus structures, hoof care, as well as conformation, can also contribute to the condition. Strain and sports-related injury from highly physical disciplines requiring hard turns, fast stops, lateral movement, and jumping, can also compound the problem, Peters says.
Initial signs can include the dressage horse that doesn’t want to lengthen or extend the trot, the hunter who starts knocking rails or stopping before jumps, or the horse that becomes unbalanced or nods its head when asked to trot a small circle, Peters says.
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