The sacroiliac is a joint that attaches the pelvis to the spine. When the three ligaments that surround and stabilize this joint are stretched or torn, the part of the pelvis called the ileum slips upward. That is the bump that you can see along the top of your horses’ rump. It is common in horses that jump, but it should be treated before it escalates into a career ending problem. The ilium is often broken when you can see this bump. Lameness may or not occur immediately.
Since I work a lot with event horses, I have seen many cases of this misalignment. Often, treatment will consist of calling a chiropractor for several treatments (count on about 6 spread over a year), stress point therapy (the muscles of the gluteus must be released in order for realignment from the chiropractic treatment to stick), cold laser, ice when the injury is new and painful, Traumeel rubbed into the area, and myofascial release.
A note of caution: Young horses who are jumped too high for their developing bodies are extremely prone to jumpers’ bump. No matter how talented your baby (under 6 years old) is, it is better to develop that talent on the flat than to jump big fences. A horse I work on regularly ran 56 races in his career on the track, but he didn’t jump until age 7. He is now 23 and still jumping (with great joy!) weekly and competing in eventing. His bodywork, excellent breeding, and good care are partially responsible for his longevity, but I also think the fact that he did not jump until a more mature age worked to his advantage.