Has there has been an increase in hind limb lameness since the round pen has become more popular? I feel like I ruined my dream horse with round pen work starting when he was about six months old. He is nine now and mostly unridable due to a degenerative condition in his hips. I had written this off as bad luck until my friend's mare began to exhibit the same problem. The only things these two horses have in common are strenuous round pen sessions and similar hind limb malfunction.

The malfunction is such that when the rear leg is brought forward for a stride, it feels as if the horse stumbles, hits a rock, or stubs his toe. From the ground, it looks as if the whole leg collapses when weight comes onto it. This is most likely to happen at a downward transition. My horse has been examined by seven vets, including the head orthopedic surgeon at the North Carolina State veterinary hospital. They did many manual exams and suggested bone scans (which I couldn't afford) and found inflammation and soreness in the hip. They offered no opinion for treatment success because they weren't sure if the injury was primarily a bone or soft tissue problem without a bone scan.

I know the experiences of two horses aren't hard evidence, but I'm wondering how many other people are dealing with hind limb lameness in horses started in round pens. 

One of the difficulties in answering the question is not all trainers use the round pen in the same manner and for the same reason. Many trainers only use the round pen for young horses, while others use this type of exercise for mature animals. Also, round pen construction and footing is quite variable