Stress diaphyseal fractures

Tibial stress fractures only occur in horses used for racing.
Clinical signs include moderate to severe hind limb lameness with no obvious heat, pain or swelling.
The fractures may be bilateral. They are typically found as part of a lameness evaluation when causes of lower limb lameness have been ruled out.

Because of the absence of local signs and the inability to perform regional anesthesia of the proximal tibia region they are detected using radiography and/or nuclear scintigraphy.
Diagnosis is based on the presence of callus in the proximal caudal lateral or caudolateral mid-diaphysis indicating ongoing bone remodeling.

Tibial fractures usually develop as a result of trauma, such as kicks or falls. The exception to this are tibial stress fractures, which are an accumulation of cyclic loading and bone fatigue.

The most common types of tibial fractures are:

1. Salter Harris Type II
2. Tibial crest fractures
3. Simple diaphyseal fractures
4. Comminuted diaphyseal fractures
5. Diaphyseal stress fractures
6. Medial malleolus fractures
7. Lateral malleolus fractures
8. Distal physeal fractures

Radiography provides the most meaningful information as to location and configuration of the fracture(s).
In most cases 4 views at 45 degree intervals provide adequate information for an exact diagnosis. For the evaluation of the proximal tibia typically a lateromedial and a caudocranial projection each is enough.
Nuclear scintigraphy is useful in the identification of tibial stress fractures, which may be radiographically inapparent.

In acute cases (less than 2 weeks) some horses with tibial stress fractures have minimal to no radiographic changes, but nuclear scintigraphy reveals marked uptake of the radio-pharmaceutical consistent with a stress fracture (arrow).