I don't know everything about it, so hopefully others will weigh in. Over at the knee is a conformational default, where from the side of the horse it looks like the front legs are not straight, that they are almost buckling, when the horse is standing still and square. The knee is bent slightly forward. Back at the knee is when the knee looks bent back, when the horse is standing upright. Either way, if you were to draw a straight line from elbow to hoof, the line would not be straight, but (inthe case of the forearm line and the lower leg line would have a break at the knee, with an angle to it.
No, it is not correctable. Most horses who have it are born with it, and you can often determine that it isn an inherited trait. That said, many many successful racehorses and jumpers are over at the knee and it affects them not at all. Back at the knee, I can't comment on.
Here is a good page which describes different front leg conformation issues, including 'over at the knee.
I agree with JB--I should know because I own one! But my horse has two club feet and is VERY sensitive to his trim. Take a millimeter too much heel and he stands over at the knee. We radiograph him regularly to keep him happy.
Originally Posted by EquineImagined
My subconscious is a wretched insufferable beotch.
My once-in-a-lifetime horse was OATK -- significantly. I bought him that way at age 12. He was a Pony Club horse. Competed in 1st level dressage finals in KY. Did cross country. Jumped. With me he did trail and horse-camping. Extremely sure footed on narrow trails. He did everything and anything I asked. We got ourselves into some pickles and he always got us out. Tangled legs in brambles, stuck in an artichoke field, caught in quicksand. Those legs were never a problem!
He looked like he might fall over when he slept -- his front legs would wobble and waver a bit. People would call me and let me know he looked like "something was wrong." Under sedation I was positive he would be the first horse that really DID fall over. Nope. Never happened. He lived til 25 and I finally lost him to arthritis. He was never lame.
(He had really good feet, and a great farrier, so now I have to go find the Equus article...)