Navicular bone oedema and sclerosis: current concepts on best management

Pathology associated with the navicular bone remains a common cause of forelimb lameness in horses. Since the introduction of advanced imaging modalities (particularly magnetic resonance imaging) it is now recognised that pathology of the navicular bone rarely occurs in isolation; concurrent abnormalities of the structures of the podotrochlear apparatus are often present. Different pathological processes of the navicular bone can have the same radiological appearance. Identifying the underlying disease process, as well as concurrent injuries, is essential for implementing the most appropriate management strategies in horses with navicular bone pathology. Horses with acute onset lameness or soft tissue injuries will often require a period of rest initially, whereas horses with chronic insidious lameness and no soft tissue pathology may be able to continue in work following treatment. Pathology associated with the navicular bone and structures of the podotrochlear apparatus are a common cause of forelimb lameness in horses, with abnormalities identified on magnetic resonance imaging examination in 72–91% of horses with lameness localised to the foot (Dyson et al, 2005; Murray et al, 2006). Since the introduction of advanced imaging modalities, particularly magnetic resonance imaging, veterinary understanding of navicular syndrome has improved sub-stantially. Navicular syndrome is a chronic, progressive condition affecting structures of the podotrochlear apparatus including the navicular bone, navicular bursa, deep digital flexor tendon, collateral sesamoidean ligaments and distal sesamoidean impar ligament that is often associated with lameness. Radiography remains the most commonly used diagnostic imaging modality in the initial investigation of horses with suspected navicular syndrome. The limitations of radiography as a sole diagnostic tool in horses with lameness associated with the podotrochlear apparatus are well recognised. It is rare to have abnormalities of the navicular bone in isolation. There are a variety of forms of navicular bone abnormalities that can be identified on radiography, including sclerosis of the spongiosa (medullary sclerosis), flexor cortex erosions, remodelling of the proximal border and extremities of the navicular bone, distal border fragmentation and cyst-like lesions within the navicular bone. In horses with suspected navicular syndrome, correct identification of the underlying disease process in addition to identification of concurrent pathology of the adjacent soft tissue structures is key to selection of the most appropriate management protocol for individual cases. This requires the use of advanced imaging techniques such as magnetic resonance imaging. Another abnormality of the navicular bone which can be identified using magnetic resonance imaging is the presence of bone oedema-like signal pattern. These radiological abnormalities of the navicular bone can represent different disease processes. The clinician must be cognisant of this and that both reversible and irreversible lesions of the navicular bone have been associated with the same signal patterns on magnetic resonance imaging.