Navicular syndrome in equine patients anatomy, causes, and diagnosis.

Navicular syndrome is a chronic and often progressive disease affecting the navicular bone and bursa, deep digital flexor tendon (DDFT), and associated soft tissue structures composing the navicular apparatus. This syndrome has long been considered one of the most common causes of forelimb lameness in horses. Diagnosis of navicular syndrome is based on history, physical examination, lameness examination, and peripheral and/or intraarticular diagnostic anesthesia. Several imaging techniques (e.g., radiography, ultrasonography, nuclear scintigraphy, thermography, computed tomography [CT], magnetic resonance imaging [MRI]) are used to identify pathologic alterations associated with navicular syndrome. Radiographic changes of the navicular bone are not pathognomonic for navicular syndrome. Additionally, not all horses with clinical signs of navicular syndrome have radiographic changes associated with the navicular bone. Therefore, newer imaging modalities, including CT and especially MRI, can play an important role in identifying lesions that were not observed on radiographs. Navicular bursoscopy may be necessary if the clinical findings suggest that lameness originates from the navicular region of the foot and if other imaging modalities are nondiagnostic. With new diagnostic imaging techniques, clinicians are learning that anatomic structures other than the navicular bursa, navicular bone, and DDFT may play an important role in navicular syndrome.