Tarsal bones: Central comminuted fractures

Comminuted fractures of the central tarsal bone in horses generally occur during racing or jumping and are seen significantly more often in sport horses.

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 the bone to failure.

Fractures of the central tarsal bone are simple (left) or comminuted (right).
Most simple fractures occur in the medial part of the central tarsal bone, and have a dorsomedial-plantarolateral orientation and involve the lateroplantar indentation of the bone.
Central tarsal bone fractures are mostly closed fractures.

Common clinical findings include heat over the affected region, signs of pain on palpation of the dorsal aspect of the tarsal region and lameness. Lameness caused by a fractured central 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 central 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 central 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 chances to detect fracture lines.
Hairline fractures are easily overlooked, and superimposition of the tarsal bones of the complex tarsal joints may obscure complicated fractures. These fractures may only be visible as very narrow lines in one particular radiographic view (left). Acute non-displaced fractures are easily missed.

Several additional oblique projections, each differing by 10°, in addition to routine dorsopalmar, 45° dorsomedio-plantarolateral and 45° dorsolatero-plantaromedial views are recommended.

Nuclear scintigraphy and especially computed tomography are very helpful and often necessary to confirm the diagnosis. Computed tomographic examination is instrumental for the detection of sclerosis because in general, bone sclerosis at a fracture site in the central tarsal bone is very difficult to diagnose radiographically.