Improper structure of the knee causes excessive stress that can lead to issues with horse health and performance.
“You want straightness in that column of bone,” according to veterinarian Dr. Jerry Black, director of the equine program at Colorado State University.
“It’s just as important as straightness in the side view. It determines how weight distribution and concussive force is handled by the leg,” Black explained.
Abnormality in straightness puts undue pressure on the joints and ligaments.
“Deviations in the knee compromise the horse’s ability to receive concussion equally on the inside, the outside of the knee and the entire front limb, as he bears weight.” and receives concussion.”
When a horse is “in at the knee,” or knock-kneed,” the knee angles to the inside of that imaginary plumb line.
“In that deviation, called carpal valgus, the knee sets far to the inside of where it should normally set and the cannon bone is displaced laterally, to the outside of the knee,” Black explained. “There is significantly more stress placed on the inside of the knee.
“Those horses are much more prone to secondary arthritic changes and may tend to have bone chips,” he continued. “They do not stand up well to a significant amount of performance stress.”
It’s common to see the condition in newborn foals, but they generally grow out of it.
“Foals born significantly knock-kneed should certainly have limited exercise, because their bones are just not mature enough to take that stress in the knee,” Black said. “Foals should be kept on stall confinement until they get more strength, but most of those deformities typically correct themselves within 60 days.”
A condition called Osteochondritis Dissecans (OCD) is a disorder that usually causes joint pain and swelling in young horses, according to veterinarian Dr. Wayne McIlwraith, equine joint researcher at Colorado State.
“This condition actually occurs when the bone and cartilage form incorrectly, causing the cartilage at the end of the bone to separate,” McIlwraith said.
Severe cases cause obvious lameness, but minor cases can be hard to detect. “These horses may go on to have an athletic career and only develop clinical signs when they’re three to five years old,” McIlwraith explained.
“Treatment for OCD typically requires arthroscopic surgery, left untreated, OCD can end a horse’s athletic career,” McIlwraith emphasized.
Veterinarian Dr. Paul Edmonds of Equine Sports Medicine at Weatherford, Texas, said one of the earliest signs of OCD to watch for in young horses is joint swelling, caused by increased synovial fluid.
“I liken OCD to human heart disease. We all have various levels of genetic tendency toward heart disease. If we’ve got good genes, we can afford to be fat and lazy and not exercise,” Edmonds said. “If we have bad genes, even all the exercise and perfect diet in the world might not protect us.
“The No. 1 prevention method is to make good use of a pre-purchase exam, including radiographs and X-rays of a horse’s joints, before you buy him and bring him home,” Edmonds pointed out.
“It’s not in every horse, but I think it’s out there enough that if I were a buyer and putting a lot of money into a horse, spending some money on taking the X-rays would be warranted,” Edmonds summarized.