The term “open knees” is misleading. The process a young horse goes through as his bones develop and his knees “close” actually involves the growth plate, not the knee joint.
The growth plates, which are above and below the joint, are modified forms of cartilage that calcify and lengthen the bone. The lower growth plate closes early in life, so it’s the top one you’re really concerned with.
There are two different types of closure. There is physiologic closure, which is when the bone is finished growing. This is mostly genetically determined. Then, there’s radiographic closure. That means that physiologic closure occurred and you can see with x-rays that the bone is totally calcified. You can’t see the line where the cartilage was.
If you think you can determine this by feeling the horse’s knee, think again. It’s tough to see any of this from the outside, said Ross Cleland, DVM, Carlton, Ore. He advises you to x-ray the knees to see how the closing is progressing around 24 to 30 months of age. Larger breeds may continue into their three-year-old year.
Many owners incorrectly connect size with physically maturity, but that’s just not the case. It’s like a six-foot-tall eighth-grade kid. He’s just bigger than the other kids, not more physically mature.
Many halter horses are worked too hard at an early age, some starting before they’re weaned, so they’re ready for futurities. However, the concussive forces when they’re on lunge lines and worked in circles can be especially rough on the knees.
When a horse plays out in the pasture, those concussive forces are somewhat healthy, because bone responds to the stimulation. The pastured horse isn’t usually running in a 60-foot circle, as with the young horse that is lunged. Lungeing puts more force on the legs, especially on the inside leg of the circle. It has a torquing effect that is especially hard on young horses. The smaller the circle, the harder it is.
Add to that the fact that many show horses are over-fed to encourage growth. This adds weight to immature bones. By the time the horse is old enough to ride, he may already be experiencing some inflammation in his growth plates. Having the knees x-rayed before starting a horse under saddle is a sound precaution.
Pay close attention when feeding young horses to give them a balanced ration with adequate levels of minerals, especially the calcium-to-phosphorus ratio, to encourage normal skeletal development (see January 2002). A young horse fed an inadequate or unbalanced diet is likely to experience even more problems if you start riding him with open knees, especially if you ride him hard.
The most common problem you may encounter is the creation of an inflammation in the growth plate. Note: You can also have damage to the knee joint, but that’s a separate issue over the growth plate being open or closed.
In some cases, if the growth plate is inflamed, it causes abnormal bone development. You might not see anything externally unless the growth plate is inflamed enough that it starts to flare out on the inside or outside edge. This calls for veterinary attention and x-rays. In a worst-case scenario, if the growth plate is still open and the young horse is subjected to over-zealous or incorrect exercise, there could be a fracture in that area.
Training Without Problems
Luckily, normal starting under saddle takes a fair amount of ground training and light riding before the young horse can be ridden extensively. In this case, riding a young horse whose knees aren’t completely closed doesn’t necessarily spell disaster. Keep things slow, easy and skip the tight circles. Done right, the whole training process is somewhat protective, in that there are few horses you can saddle up after a week and ride the pants off of.
Many racehorses do start training late in their yearling year, with trainers arguing that galloping a young horse stimulates the knees to close. But remember the Thoroughbred industry doesn’t routinely lunge its horses in small circles. The young horse is usually on a training track or in a pasture with soft footing. They’re working mostly in straight lines without tight turns. Even so, young horses in training are at high risk for physitis (growth-plate inflammation) and problems involving the joint itself.
If you have any doubt about where your two-year-old is in the knee-closing process, get x-rays. If everything is progressing normally, he’s ready to ride. Talk with your vet, but err on the side of caution. A little more time isn’t much to sacrifice over the course of the horse’s career.
Also With This Article
Click here to view the Knee Joint Diagram and ”Use The Foaling Date.”