What are Third Trochanter Fractures in Horses?

Ever heard of the horse's third trochanter? It's a part of a bone, and guess what: It can break. While not common, third trochanter fractures can cause almost instant, severe hind limb lameness that can be difficult to diagnose. But the news isn't all bad: French researchers say these fractures probably won’t end a horse's athletic career and generally heal without surgery.

“The third trochanter is a bony process that is neither a joint nor a weight-bearing surface, making these fractures far better tolerated in the horse,” said Lélia Bertoni, DVM, researcher and practicing veterinarian at the Centre d'Imagerie et de Recherche sur les Affections Locomotrices Equines in Normandy.

The third trochanter is located on the outside surface of the femur bone, about halfway between the hock and the hip. It’s called the “third” because there are two other trochanters: the “greater” trochanter (a large process at the top of the femur) and the “lesser” trochanter (a smaller process to the side of the top of the femur). A bony process is a perfectly healthy and normal bony bump that protrudes from a flatter bone surface. The third trochanter bump provides an insertion point for the gluteus superficialis muscle's tendon.

Bertoni and colleagues recently investigated eight cases of third trochanter fractures in a first-ever review of the condition. They found that the significant muscle mass around the trochanter makes it difficult to see any kind of obvious physical manifestation of the fracture, such as swelling or even tenderness when touching it, she said. That same mass also makes getting a good X ray view of trochanter processes practically impossible without high-level machinery in a clinical setting. Further, there is no clear, characteristic lameness of a third trochanter fracture.

Ultrasound, however, is very useful in locating such a break. “An accurate diagnosis can be very easily obtained by a rapid ultrasound investigation—which is easily available to clinicians, noninvasive to the horse, and relatively inexpensive for the owner,” said Bertoni, adding that this has never been reported in previous scientific reports for such fractures. An ultrasound investigation could replace a costly set of hind-end radiographs as the treating veterinarian searches for a cause of lameness, she suggested.

Further complicating such fractures is the fact that few people are aware of the third trochanter, or that it can break, Bertoni said. In the study cases, none of the owners or trainers had heard of this kind of fracture. Even so, its protruding shape makes it susceptible to damage during falls or traumatic injury to the hip, such as a collision against a doorway or trailer barrier.

But on the plus side, treatment is simple: stall rest with progressive exercise as the lameness permits. “The activity level should be adapted to the degree of lameness rather than to the ultrasonic or radiographic appearance of the lesion,” Bertoni stated in her study report. For the eight study horses, this meant one month of stall rest, one month of hand walking, and two to four months of light exercise in a small paddock before returning to full athletic activity. Half the horses also received a non-steroidal anti-inflammatory (NSAID) for one to two weeks to help with the pain and swelling, she said.

All but one of the eight horses went on to full athletic potential; the final horse had ongoing lameness and was finally retired, but for reasons other than its third trochanter fracture.

“Prognosis is favorable and healing spontaneous,” Bertoni said.

The study, "Fractures of the third trochanter in horses: 8 cases (2000-2012)," was published in the Journal of the American Veterinary Medical Association

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.