Surgical Repair of Hock Fractures in Sport Horses Successful

Central tarsal fractures develop across or through the bone, highlighted here on a CT image by yellow arrows. Sclerosis, indicated by a yellow arrowhead, surrounds the fracture.

Photo: Courtesy Dr. Jan Kuemmerle

While veterinarians often recommend conservative treatment before surgery for many equine health problems, the healing of a central hock (or tarsus) fracture isn’t something you want to just wait around for. Swiss researchers have learned that prompt surgery—particularly screw fixation—is the best way to get your sport horse sound and back to work as soon as possible.

“Once a central tarsal bone fracture is diagnosed, lag screw osteosynthesis (bone repair using screws) is associated with a very good prognosis,” said Jan Kuemmerle, DrMedVet, Dipl. ECVS, of the Equine Hospital at the University of Zurich’s Vetsuisse Faculty.

“However, it is important that this is performed in a hospital with excellent intraoperative diagnostic imaging capabilities—computed tomography (CT) or fluoroscopy (real-time radiography)—to allow exact placement of the screw,” he added.

Like racehorses with tarsal bone fractures, affected sport horses typically present with sudden, acute lameness that turns into mild to moderate lameness after a couple of weeks. And in both groups of horses, untreated fractures can lead to arthritic changes in the adjacent joints that can cause permanent damage. So rapid diagnosis and surgery are vital to the horse’s athletic future.

However, fracture patterns in sport horses are different from those in racehorses, Kuemmerle said. Racehorses often have dorsal fractures (located on the front of the bone), whereas sport horses—primarily jumping horses—develop central tarsal bone fractures in the sagittal plane, meaning the break occurred across or through the bone.

Such a fracture is therefore difficult to diagnose with typical radiography, and the veterinarian might miss the insult on initial screens, Kuemmerle said. Lateromedial X rays (which are shot from the side) can help, but CT scans appear to be the gold standard for central tarsal bone fracture diagnosis in sport horses.

In their study, Kuemmerle and colleagues investigated six sport horses (five show jumpers and one reiner) diagnosed with a central tarsal bone fracture at the Vetsuisse Faculty. All the horses underwent surgery at the hospital for screw placement following a CT scan under general anesthesia to precisely identify the location of the break—a critical point, Kuemmerle stressed.

This postoperative radiographic view shows the lag screw in correct position.

Photo: Courtesy Dr. Jan Kuemmerle

“There is little space in the small tarsal bone, therefore little space for errors, and an imperfectly placed screw might have catastrophic consequences (such as permanent lameness),” he said.

All five jumping horses returned to their normal performance level after a convalescence period of six to nine months, including four months of stall rest post-surgery, Kuemmerle said. However, the reining horse had continued lameness.

That lameness was probably not related to his discipline but to the fact that this horse had different lesions in his hock bones, he said. He had osteoarthritic changes in the joints but very little new bone growth related to the fracture—suggesting that the fracture occurred because of the osteoarthritis, and not the opposite. In that case, the treatment could not reverse the lameness caused by the osteoarthritis, he said.

Jumping horses probably develop central tarsal bone fractures as “stress fractures” from ongoing wear and tear on the bones, rather than a traumatic injury, Kuemmerle noted.

“All the horses in our study had evidence of bone remodeling (sclerosis) typical of chronic stress,” he told The Horse. “So probably the forces that act chronically on the bone in jumping horses can lead to sclerosis.

“Sclerosis increases bone density but also makes it more brittle,” he said. “Then microcracks can develop that typically cannot be recognized clinically and radiographically. With continuous use of the horse and accumulation of microcracks, a fracture can develop.”

Surgery by qualified veterinary surgeons can give owners every reason to be optimistic, especially if the problem is treated quickly before osteoarthritis sets in, Kuemmerle said.

The study, “Central tarsal bone fractures in horses not used for racing: Computed tomographic configuration and long-term outcome of lag screw fixation,” will appear in an upcoming issue of the Equine Veterinary Journal

About the Author

Christa Lesté-Lasserre, MA

Christa Lesté-Lasserre is a freelance writer based in France. A native of Dallas, Texas, Lesté-Lasserre grew up riding Quarter Horses, Appaloosas, and Shetland Ponies. She holds a master’s degree in English, specializing in creative writing, from the University of Mississippi in Oxford and earned a bachelor's in journalism and creative writing with a minor in sciences from Baylor University in Waco, Texas. She currently keeps her two Trakehners at home near Paris. Follow Lesté-Lasserre on Twitter @christalestelas.

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