He presented about the causes, diagnosis, and treatment of horses with changes to their navicular bone and surrounding tissues during the Northeast Association of Equine Practitioners Convention, held Sept. 21-24, 2022, in Saratoga Springs, New York.
Causes of Navicular Syndrome
Pittman described the two root causes of navicular problems: developmental and biomechanical.
“In these cases the horse isn’t always lame but there is a radiolucent lesion of the navicular bone on X ray,” he explained. “This is thought to be a defect in how the bone forms and can be found on young horses without lameness. While it might not initially be painful, it alters the structure of the navicular bone, which can ultimately affect how it interacts with the deep digital flexor tendon (DDFT, which runs from the back of the knee or hock down around the navicular bone and inserts on the coffin bone in the foot).”
For example, the flexor surface of the navicular bone—which borders the DDFT—can have an indentation. As a result, the DDFT doesn’t course over a smooth surface. As the lesion matures, the edges become roughened, causing inflammation of the DDFT and the bursa (the sac cushioning the navicular bone from the DDFT).
“I consider this occurrence similar to osteochondritis dissecans,” said Pittman. “They both occur early in a horse’s life but don’t tend to turn into problems until later.”
“In this scenario we’re mainly dealing with chronic overload of the soft tissue components of the navicular apparatus—the DDFT, suspensory ligament of the navicular bone, and the impar ligament,” Pittman said. “Predisposition is secondary to the structural biomechanics these cases are born with.”
Typically, a long toe lever with the center of rotation of the coffin joint positioned closer to the back of the hoof creates a greater lever arm predisposing horses to navicular syndrome, said Pittman.
Despite the focus on the navicular bone itself, Pittman said most of the time, we aren’t dealing with the navicular bone alone.
“You need to consider the whole picture and all the factors that could affect your shoeing, such as crushed heels, thin soles, club foot, and coffin joint arthrosis,” he said.
Diagnosing Navicular Syndrome
Lameness can be variable, but horses with navicular syndrome typically have a bilaterally (affecting both sides) lame, short, stabby gait, especially on tight turns, and the horse often lands toe-first. These horses also often have sore heels when tested with a hoof tester. The lameness resolves with a lower palmar digital nerve block, which numbs the back third of the foot.
“Magnetic resonance imaging (MRI) is the gold standard diagnostic tool for complete soft tissue and bony imaging, but it is cost-prohibitive in many cases and might require general anesthesia,” Pittman said.
In lieu of MRI, Pittman uses ultrasound to identify potential linear lesions of the DDFT that run up into the pastern. He warned that these cases require a longer rehabilitation period.
Radiographs tracking changes in the navicular bone are a requisite for managing horses with navicular syndrome. In Pittman’s opinion, the most descriptive views are the high-beam horizontal dorsopalmar view centered 1 centimeter distal to (below) the coronary band and a 65-degree dorsopalmar view.
“That said, there is not one specific view that will give you all the information you need,” he said. “What is probably most important is to reliably reproduce the same image for the serial follow-up evaluations.”
To demonstrate his point, Pittman showed several pairs of X rays of the same navicular bone taken at slightly different angles. The slight change in angle resulted in dramatic changes on the appearance of the navicular bone. “The repeat images don’t even look like they’re from the same horse,” he said.
He showed one example of images obtained using traditional skyline views.
“If the angle of serial images changes even slightly, it can actually look like a cystic lesion is getting smaller,” Pittman explained. “But in reality, the entire bone looks different because the angle really isn’t repeatable.”
Therefore, it is necessary to evaluate the distal half of the flexor surface of the navicular bone where most of the problematic lesions occur to make an accurate diagnosis.
“Pick radiographic views that will highlight these areas with good angles and limited distortion,” advised Pittman.
Treating Navicular Syndrome
“Always start with mechanical treatments. Medical therapy is always complementary,” Pittman said.
“All my cases get a rocker shoe, I’m not going to lie,” he added. “These shoes greatly reduce the toe lever and reduce resistance against the DDFT and the navicular bone.”
Pittman aims to determine the level of mechanical shoeing needed relative to the horse’s unique pathology and rehabilitate these cases appropriately to prevent further damage or soft tissue pathology.
“Remember that you are just moving weight to a different spot with the shoeing,” he said. “An appropriate rehabilitation and exercise program relative to the degree of damage is important so you don’t cause any new problems while trying to fix the original problem.”
What can you return to a normal shoe? “When you have a normal navicular bone,” said Pittman. “So possibly never.”
Monitor navicular syndrome cases consistently, said Pittman, and track changes with pre- and post-shoeing X rays, being careful to use reproducible and consistent views and angles.