Based on more than a thousand MRI exams at Washington State University (WSU), Robert Schneider, DVM, MS, an equine orthopedic surgeon at WSU, reports that the magnetic resonance imaging (MRI) will locate the pathology of navicular disease 90% percent of the time. Schneider spoke about equine foot lameness at the Western Performance Horse Forum held in Nampa, Idaho, on Feb. 15-17.

In general, radiographic signs of navicular disease do not correlate well with clinical signs until there is end-stage disease. Previously, navicular disease was based on a clinical diagnosis, but now it is also identified via MRI.

Schneider noted that a common question asked is: "How will an MRI change how I treat my horse?" After identifying the region of pain with diagnostic nerve blocks, he explained that the MRI pins down the problem; knowing the specific problem affects all further strategies such as medication, rest, arthroscopic surgery, or retirement from active athletics. Rest is expensive, especially since it often takes three to six months for resolution of a foot problem. With a subtle problem, an owner might want an immediate answer to avoid time off without risk of injuring the horse.

A large group of horses that developed clinical signs of navicular disease during the six months prior to exam were scanned with MRI. These horses demonstrated typical signs of bilateral forelimb lameness, sensitivity to hoof testers over the middle third of the frog, and diagnostic nerve blocks of the heel region that improved one leg only to worsen the other limb, which went sound with a heel block. Interestingly, all these horses had normal radiographs