Navicular disease is a differential diagnosis for lameness involving stay apparatus structures.

• A. Distal sesamoidean ligament injury
• B. SDFT/DDFT tendinopathy
• C. Suspensory ligament desmitis
• D. Navicular disease

Answer: (D)

The idea being tested is recognizing diseases that cause lameness through the stay apparatus, with the navicular apparatus as a central component. Navicular disease directly involves the navicular bone and its associated soft tissues (navicular bursa and related ligaments/tendons), so it is a classic cause of lameness localized to the heel area and a primary differential when the stay apparatus is involved.

While distal sesamoidean ligament injuries, SDFT/DDFT tendinopathy, and suspensory ligament desmitis can also produce stay-apparatus–related lameness, the statement is pointing to navicular disease itself as the differential diagnosis in question. That makes navicular disease the best match.