Page 56 - July 2020

EQUINE HEALTH
Cartilage that would ordinarily turn into bone at growth zones builds up without ossifying, thereby creating abnormally high pressure in the physis.
Treatment for cysts is a little more com- plicated than for fragments, and they also do not have such a good prognosis. “The first line of treatment would be to inject the joint with cortisone and rest the horse,” he says. “Take the horse out of training, confine it
for 3 months in a stall to reduce the stress
on the joint. The reason for this conservative approach is two-fold. First, the cysts don’t respond so well to surgical treatment. Second, there is a better chance of the inflammation settling down with rest and injections than for dissecting lesions in OCD. The latter separa- tions will never heal back on. But the cysts can either fill in or settle down sufficiently to stop irritating the joints, and stop causing it to stay inflamed.
“This approach only works with young horses, however. The older the horse, the less effective the rest and joint injections will be. If confinement and rest do not work, then the only option is surgical treatment. The main approach is to debride the content of the cysts (scrape the surfaces) since these cysts tend
to have an inflammatory lining. Once this lining has been removed, some surgeons inject cortisone into the bone (where they’ve just scraped out the lining of the cyst). Others put a bone graft in to try to fill the cyst. Others put cartilage cells or stem cells in a fibrin glue (cells harvested from elsewhere in that horse) in to fill up the cyst,” he says.
The surgical treatment of bone cysts
is more complicated than dealing with a dissecting bone fragment, and the outcome
of the surgery is less predictable. Some
cysts may even become larger as a result
of surgery. For this reason, some surgeons inject cortisone directly into the cyst during arthroscopic surgery, without scraping out the contents of the cyst. The outcome of cyst surgery has been shown to be directly related to the horse’s age.
“The older the horse, the less likely the surgery will be successful. There are also some breed predispositions. Quarter Horses tend
to have a less favorable outcome after surgery than Thoroughbreds, for instance. We don’t know why, but we think it may have some- thing to do with conformation of the stifle in Quarter Horses. Many of them have a steeper angle (a more upright stifle), and the joint is more prone to trauma,” says Schramme. There is more stress on that type of stifle.
Dr. David Frisbie at Colorado State University has worked with many stifle problems and says the bone cysts may have an osteochondrosis origin in young animals, but can also occur in adult horses after trauma. There are also varied radiographic appear- ances. “In some cases, a radiograph will
show a big hole in the bone—maybe 3⁄4 inch in diameter,” Frisbie says. “These typically occur in the medial femoral condyle of the stifle. These lesions can vary from just being a flattening of the condyle to a crescent-shaped divot, to a divot that’s 5 mm deep, to a full- blown cyst.
“We often see these bone cysts/flattening’s on pre-purchase films, and they are not always associated with lameness. We’ve done some work in which we looked at repository films, and many of these horses were not lame.
“We looked at long-term performance out- comes, in 3 and 4-year-old horses, and didn’t see a high association with flattening on the condyle based on the repository findings,” says Frisbie.
When people see these changes on the con- dyle on pre-purchase radiographs, they may not understand that these may not be a big problem. “This is something that has changed in our general knowledge, realizing that not all abnormalities on the condyle will become a problem,” he says.
“Subsequently, we’ve been able to develop a new technique for dealing with these. Instead of simply scooping out those cysts when
they do become a problem, we go around
the periphery of the cyst with an injection. There’s a lining that produces chemicals that retard healing of the bone. If we decrease the metabolism of that lining, depending on who is doing the surgery, we can get 80 to 90% of those horses back to full work within 2 or 3 months,” he explains. This is a good prognosis for most of the horses.
PHYSITIS
Inflammation of the growth zone or physis at the ends of the long bones creates pain
and enlargement, and usually occurs in fast- growing foals and weanlings. The cartilage
that would ordinarily be turning into bone at these growth zones builds up without ossifying, thereby creating abnormally high pressure in the physis.
“The best way to deal with this is to slow down the growth of the foal and restrict exer- cise,” says Schramme. Exercise puts additional stress and pressure on the thickened growth plates. To adequately slow down growth (depending on the age of the foal) may mean weaning it early or reducing carbohydrate intake in the weaned animal.
“With any of these diseases, make sure that trace elements are adequately present in the diet. There must be a proper balance, especially of vitamins and minerals. Supplements can be used, if needed, to balance the diet. Particularly important are the calcium/phosphorus ratio, and the presence of adequate levels of copper in the diet,” says Schramme.
ARE SOME OCD LESIONS NORMAL?
There is research evidence that the dissect- ing (fragmenting) lesions on the bone surface
of a joint can keep changing and even repair themselves, up to about 5 or more months of age: for the hock, up to 5 months of age, and for the stifle, up to 8 months of age. “This research data is from Holland, where they’ve done a lot of excellent work studying this condition in Dutch Warmbloods, since there is incidence
of OCD in about 30% of Dutch Warmblood foals,” says Schramme. “Scientists from the University of Utrecht followed a number of these foals through the first months of life. They found evidence of lesions at 3 months in many foals, but at 5 to 6 months these lesions were gone. So, the researchers hypothesized that a potential repair process exists early in life.
“The same potential would apply to bone cysts,” he says. “The reason for this is that
in young animals up to about a year of age, cartilage can repair itself. It has blood flow
and a high metabolic rate while the horse is
still growing. Once a horse is about a year old, however, this tissue becomes set and does very little. Cartilage itself, as a tissue, is almost inert. Finding an articular cartilage lesion in
an older horse is bad news because it will never repair itself. Cartilage will only continue to degenerate further. But in foals, there is a repair capacity. There’s a window of opportunity, which according to some authorities goes to 8 months, in which cartilage can self-repair in some of these lesions.
“We used to think radiographic evidence of OCD in a horse, even if it was a foal 2 to 3
54 SPEEDHORSE July 2020