Slab fractures of the third tarsal bones occur during racing or other high-speed events.
They are seen significantly more often in Standardbreds than in Thoroughbreds or other breeds. Moderate to severe sclerosis can often be seen along the fracture line on CT images. This is indicative of trabecular thickening and increased mineral bone density, which predispose bone to failure.
Fractures of the third tarsal bone usually are closed and present as simple fracture patterns.
Common clinical findings include heat over the affected joint, signs of pain on palpation of the dorsal aspect of the tarsal region and lameness. Lameness caused by a fractured third tarsal bone varies from severe to moderate in the acute phase, but diminishes to become moderate or mild one or two weeks later. It is usually first noticed during or after fast work or racing.
Flexion of the hind limb will elicit a positive reaction in horses with third tarsal bone fractures, but the test is not specific for tarsal lameness. However, with a tarsal fracture, a marked response to tarsal flexion persists for an extended period of time.
The diagnosis of a third tarsal bone fracture is generally difficult because soft-tissue swelling may be minimal, and lateromedial and dorsoplantar radiographic views may not reveal an obvious fracture line.
Therefore, multiple oblique radiographic views are recommended to improve the detection of fracture lines.