So, the ulna is continuing to grow and elongate.....and the radius doesn't.
What do you think happened?
It did awful things to the elbow joint. The ulna was growing longer and pushing the elbow joint away from the radius/elbow connection and gaps where forming in the elbow joint where there should be no gaps! It was obviously deformed, looked painful, and it was not hard to imagine the loss of function in this young dog.
As horse people (and dog people) we hear about growth plates all the time. I guess I had some vague notion that asking too much from a young animal could result in arthritis and other problems "down the road". I didn't realize the SIGNIFICANT and IMMEDIATE impact that damage to the growth plates can have on your young dog/puppy right now. There's definitely degrees of injury, growth plate closure isn't always the result, and it isn't always catastrophic....but my point is, if you damage that growth plate by overworking your young horse or dog - it isn't someone else's problem down the road, or that the animal will be more "creaky" upon retirement, or shorten their performance career by a bit - you could be killing that career before it even starts.
Seeing is believing. I'm not able to post slides from school because of copywrite limitations, however, here's an image from University of Pennisylvania's website that I found through google - in this case the bones are bending, and not necessarily destroying the elbow joint like the example I saw in lecture - but you get the idea.