Friday, June 03, 2011

Racehorse Fetlock Screening Via Standing MRI Could Identify Horses at Risk for Condylar Fractures of the Fetlock

If there is one thing that we all learned by watching the Kentucky Derby this year, it was the term "condylar fracture". Watching first Battle of Hastings and then Archarcharch load into the horse ambulance was the low point of the day.

Are you one of the people who just shrugs and says, "That's racing!" or are you one of the people who asks, "Why? Why? Why?"

Maybe this article will raise the eyebrows of people in both camps and get them both saying, "What if..."

So what if...

What if a standing MRI could help identify horses with potential fetlock problems before any injury ever even happens? It's possible, and that's the prospect that equine practitioner John Peloso of Equine Medical Associates of Ocala, Florida put forward in March in an article in Thoroughbred Times.

Little did he know how timely the article would be six weeks later!

Let's start with the injury. Condylar fracture means that the portion of the long bone that was broken was the condyle. When you look at the end of the cannon bone, you see a ridge in the middle, between two rounded bulbs, called condyles.

The fetlock joint surface can be subject to a lot of wear and tear, as well as evidence of a degenerative condition, that might now show on a radiograph but might be visible via MRI. (John Peloso DVM photo)

The condyles sit in the fetlock joint and rotate within it, like balls in a socket, as the horse flexes his lower leg. Battle of Hastings' fracture was the medial (rough translation: inner side of the limb) condyle, whereas Archarcharch's injury involved the lateral  (rough translation: outer side of the limb) condyle.

Racehorses are especially prone to condylar fractures. Something (trainers like to call it "a bad step") causes increased pressure on the condyles in the fetlock joint. Normally a horse is fine but sometimes the condyle fractures, to varying degrees. A radiograph will show what looks like a crack in the cannon bone in the condyle area.

Thoroughbreds "Make It or Break It"

In his article, Dr Peloso reminds us that the process of building and creating an equine athlete is dependent on the horse's ability to "remodel" his bones.

The rigors of training cause a horse to continually lose bone and then replace it. In a healthy normal horse, the resulting replacement is more dense than the original.

But in some horses, the lost bone is not adequately replaced or fortified. This is called non-adaptive bone modeling. The effects of training may actually weaken the bone rather than fortify it.

If you have looked at a good radiograph of a horse's fetlock and cannon bone, you know that bone has different density values, and yet the inadequate bone modeling syndrome is deep in the bone and difficult for a radiograph to show. The depth of the problem means that the tissue around the joint doesn't swell, either. It's invisible.

MRI scans the fetlock in 3-D

Which horse would you bet on? The horse on the left had not begun training; the horse on the right shows mild thickening of the subchondral bone in the condyle region. (John Peloso photo)
Dr Peloso recommends the use of standing MRI to evaluate racehorses. MRI scans the fetlock in three dimensions and shows what's going on with the soft tissue in and around the joint as well as the architecture of the bony column itself. And with standing MRI, the horse does not need general anesthesia; trainers are reluctant to schedule their horses in training for anesthesia.

Standing MRI allows the horse to stand in a natural position while the scanning goes on. The horse is sedated but does not need general anesthesia. (Hallmarq Veterinary Imaging photo)

Certainly there is no way to know how many injuries can be prevented by monitoring fetlocks for non-adaptive bone remodeling. But in human medicine, MRI is the modality of choice to routinely detect almost-invisible stress fractures in athletes.

Dr Peloso noted that standing MRI screening of the fetlock is commonly performed in England, Ireland, France and Dubai, where many vet clinics are equipped with standing MRI units and may screen as many as two to three racehorses per day.

What veterinarians like Dr. Peloso hope to help trainers avoid: two examples of the early stages of condylar fracture of the fetlock. The red arrows are pointing to white crack-like lines that indicate a fracture has begun. (John Peloso photo)
Of course, you have to wonder why this happens at all: why are some horses normal? Why is it that the bones in other horses--horses who look and act perfectly healthy--just don't adapt properly?

Those are big questions. MRI can't answer those but a racehorse monitoring protocol of standing MRI sounds like a hopeful proposal that could possibly save some American horses' lives, careers or months lost from training. It could be that famous "ounce of prevention" that is worth many pounds of surgery, layup and rehabilitative cure.

Thanks to the kindness of our friends at Thoroughbred Times, we're able to post the entire article by Dr Peloso here on the Hoof Blog. You'll find an interactive window at the end of this article. Use the controls at the bottom of the document window to enlarge the text or scroll through the pages.

To contact Dr Peloso about his work on bone remodeling in Thoroughbreds, please contact John G. Peloso, DVM, MS, Diplomate ACVS, Equine Medical Center of Ocala, 7107 West Highway 326, Ocala, Florida 34482.

To learn more about standing MRI, visit Hallmarq Veterinary Imaging on the web.

Also on the Hoof Blog:
Thoroughbred Times 032511 Hallmarq Benefits of MRI Peloso

Article reprinted with permission from
Thoroughbred Times

Disclosure of Material Connection: Hoofcare Publishing contracted to receive compensation for compiling this post but the veterinary expertise and opinions in the article were provided by John Peloso DVM and Hallmarq Veterinary Imaging.  The information contained in this article is for informational purposes only, and should not be used to replace professional veterinary advice for your horse. Visitors to the website are responsible for how they choose to utilize this content. I am disclosing this in accordance with the Federal Trade Commission’s 16 CFR, Part 255: Guides Concerning the Use of Endorsements and Testimonials in Advertising.