Chapter 31 Fracture of the Navicular Bone and Congenital Bipartite Navicular Bone
Fractures of the navicular bone occur in a variety of configurations. The most common is a slightly oblique parasagittal fracture, medial or lateral to the midline. Y-shaped fractures and other comminuted fractures are less common. Avulsion of the entire distal border is rare. Distal border fragments are discussed elsewhere (see Chapter 30). Fractures occur more commonly in forelimbs than hindlimbs. In a series of 40 horses with navicular bone fractures, 28 (70%) occurred in a forelimb.1 Fractures usually are traumatic in origin, although it is not always possible to identify the cause. Some fractures in hindlimbs have been the result of kicking a wall. Bipartite and tripartite navicular bones have also been described and should be differentiated from a fracture.2 These may occur unilaterally, bilaterally or sometimes in 3 or 4 limbs in forelimbs or hindlimbs. It has been suggested that many fractures are pathological secondary to severe navicular disease,3 but this confusion probably arises because lucent zones adjacent to the fracture line and along the distal border of the navicular bone develop rapidly, within months of fracture occurrence.4 Palmar (plantar) displacement of fracture fragment(s) may result in laceration of the deep digital flexor tendon (DDFT).5 Other fractures of the middle or distal phalanx occasionally occur concurrently.
