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Navicular syndrome is a common cause of lameness in the horse. This problem may account for 1/3 of all chronic lameness. Unfortunately, navicular syndrome remains only loosely defined.
Diagnosis is based on the characteristic gait and localization of pain to the back of the hoof and presence of radiographic changes in the navicular bone.
Navicular syndrome is almost always chronic in nature. Although the lameness may not be chronic, the horse’s change in performance is. Lameness is usually noticed if the horse is worked heavily or worked on a hard surface.
Rest often will improve the lameness temporarily, but it will return when work resumes. While navicular syndrome is usually a bilateral lameness, it can occur unilaterally.
Clinically, the diagnosis is made on the basis of characteristic gait changes, elicited pain in the distal sesamoid region of the foot and marked improvement in the lameness following a palmar digital nerve block. The horse’s gait has a shortened cranial phase of stride length and is choppy in nature. The lameness can always be accentuated by turning the horse in tight circles.
While a positive response to any of four types of diagnostic tests is important, a negative response is equivocal and does not rule out navicular syndrome.