Standing tall

Central to a range of enhanced equine welfare initiatives, the diagnostic tool is crucial to the prevention of limb injuries. 

The scanner was the subject of much debate in the week before the 2019 Lexus Melbourne Cup when European imports Marmelo and Ispolini were forced withdrawals from the race following the results of standing CT scans.

And that debate has continued with a recent international veterinary conference at Newmarket in the UK called to specifically discuss the question of reasonable risk, especially in relation to new pre-race imaging assessment methods such as the standing CT scan. While training and regulatory practices vary from country to country, the conference in Newmarket, attended by experts from all over the world, concluded that increased international collaboration is beneficial.

As international experts work together to try to gain consensus on what images mean in terms of risk profile for injury, the conference was a chance to share their own practices and look at the newer kids of advanced imaging available.

A standing MRI has been used successfully on thoroughbreds in the UK and the US, and also in the US, the first phase of the validation of the MILE-PET, the first positron emission tomography (PET) scanner specifically designed to image the limbs of standing horses, using light sedation and therefore eliminating the need for anaesthesia, has been completed.

Dr Chris Whitton, Professor of Equine Medicine and Surgery at University of Melbourne veterinary department, is at the forefront of limb injury research and diagnosis within the global veterinary community. He acknowledges that the use of the standing CT scanner is a new practice but believes the process will provide unique information regarding the condition of a thoroughbred in training.

The technology itself is not new, in our practice we’ve been using CT scanners in equine diagnosis for eight years mainly prior to surgery to identify the damaged area. - Dr Whitton

During a CT scan a “donut” capsule surrounds the area that vets wish to image, and x-rays rotate around that capsule creating a three-dimensional image of the area rather than a two-dimensional image provided by a standard x-ray.

“Traditional CT scanners require the horse to be anaesthetised and lying down; the machine also produces a lot of radiation so no medical staff can be in the room so there are some major limitations.

“The beauty of the standing CT scanner is that the subject only needs mild sedation and can be standing during the procedure. The donut comes up out of the floor and surrounds the leg right up to the hock or knee. The radiation involved is at a much safer level, so staff can be present to comfort the horse and keep him or her still.”

The development of the standing CT scanner has provided significant time saving, with results available under a minute and the entire process completed in a matter of minutes. Patient recovery is also fast, as only a mild sedative is required.

Most notably though, the scan serves as a vital early warning tool in the prevention of race day injuries.

“Most of the injuries horses get are the accumulation of damage over time rather than a one-off catastrophic event,” Dr Whitton explained.

“90% of fractures are due to high load over time. If you continually put high load on a material it will eventually weaken, and bone is no different in that regard. A large proportion of post-mortem examinations in horses with fractures shows signs of bone loss or weakening in the affected area.”

Rather than a single source of truth, standing CT scans provide a unique diagnostic measure along with more general in-stable examinations to reach an assessment of risk for each individual.

“The results are never black and white and the images from a CT scan are never the only facts we work off. There are always multiple aspects of examination to determine the risk of a horse sustaining an injury: how he or she moves, what the treatment history is, what the history of injury has been,” said Dr Whitton.

“We want to determine what the level of risk is and then to work with the trainer to determine whether the issue can be managed in training. It certainly doesn’t mean that horses with risk can’t be managed through to reduce that risk and continue racing, or that they cannot be retrained for the next stage of their life.”

Data from ongoing U-Vet research regarding catastrophic fractures is assisting Dr Whitton and his team to build strong statistical data regarding injury risk assessment.

“We’ve looked at 100 horses so far and the postmortems are showing us changes in bone pathology that doesn’t worry us at all, as well as changes that are very closely linked to fracture,” he said.

“There are going to be false positives and there will be horses out there with changes that are not dangerous, but all we can do is revert to our data and to what we’re learning. We’re focused always on the question of reasonable risk and the standing CT scanner is a big part of that.”

(Photos by Pat Scala/Racing and Karon Photography)