NAVICULAR DISEASE IN THE HORSE

Navicular disease results in a chronic, progressive forelimb lameness that is usually bilateral. Although many different horse breeds can be affected, Quarter Horses and Warmbloods appear particularly susceptib le. The peak age incidence appears to be in horses aged 6-10 years. Th e condition has been recognized for many years and has been the source of debate and conflict for at least the last 50 years. Much of the co nfusion has been caused by different criteria used to establish a diag nosis. In a large series of cases examined at the University of Sydney , only 30 percent of horses that were eventually diagnosed as having n avicular disease showed a positive response to hoof testers applied ac ross the middle third of the frog. In contrast, more than 80 percent o f horses with navicular disease showed a marked increase in lameness f ollowing pastern and fetlock flexion. All horses diagnosed became soun d following a palmar digital nerve block and all had positive findings on radiography. However, radiography could not be utilized as a sole diagnostic technique because some horses with radiographic abnormaliti es of the navicular bone did not show clinical signs of navicular dise ase. To establish a diagnosis of navicular disease, the following crit eria should be met: 1) A chronic progressive unilateral or bilateral f orelimb lameness, 2) Pain in areas proximal to the foot has been exclu ded as a possible cause of the lameness, 3) Other conditions that coul d cause pain in the palmar heel region are excluded, 4) The lameness i s eliminated or substantially improved following a palmar digital nerv e block, and 5) There are radiographic abnormalities on upright pedal and/or skyline views of the navicular bone. Treatment of navicular dis ease has usually fallen into categories of a) pain alleviation, b) dru gs with vascular or hemodynamic effects, or c) changing biomechanics e ither by corrective trimming or corrective shoeing. None of these trea tments have been universally accepted and debate about their efficacy is allied to theories about the etiology.