"With MRI we’ve found horses with coffin bone fractures that weren’t visible on X rays, but were treated like navicular horses because they blocked to the heel," says Sarah Sampson, DVM, of Washington State University. "If these are managed like navicular horses, they don’t heal because they don’t get the rest they need and are not put into a shoe that completely eliminates movement in the bone."

She recently assessed an 8-year-old Quarter Horse that had been lame for two months; the owners had turned it out to pasture for rest, thinking it was the beginning of navicular disease. Nothing showed up on digital radiographs, so vets performed MRI on both front feet. It was very clear there was a nondisplaced fracture of the coffin bone in one foot.

"This horse was not as lame as we generally see with a coffin bone fracture, so this was not suspected," she says. "With proper diagnosis, we went from a horse we thought might have the start of navicular syndrome (and in a couple of years have to be retired) to a horse that has a good chance for future soundness if treated properly."

Another case involved a 5-year-old Quarter Horse stallion that blocked to a palmar digital nerve block on a front foot. "Multiple radiographs had been taken at different times, and all were normal. He remained lame for over a year and eventually came to Washington State for MRI," she recalls. "We found he had an epidermoid cyst (abnormal, but benign, mass) in the lowest part of his digital flexor tendon sheath. The mass was impinging on the tendon. Many people don’t realize the digital tendon sheath extends through the pastern and down past the heel bulbs. We were able to go into the sheath tenoscopically and surgically remove the mass. That horse has been sound and back in performance now for over three years