A University of Minnesota study reported that of 124 cases of suspected back pain in horses seen at their clinic over five years, over half of the horses had a sacroiliac-area problem. At the University of California, researchers examined the spines of 36 Thoroughbred racehorses euthanized for unrelated reasons and found acute injury or degenerative/arthritic changes in the sacroiliac joint in all the horses. In the United Kingdom, the Animal Health Trust reported dressage and jumping horses to be high risk for sacroiliac region pain. Clearly, the sacroiliac region needs to be seriously considered any time a horse is off behind or has back pain. What Is The Sacroiliac? The sacrum is the end portion the horse's spine. If you press a finger firmly along the middle of the horse's back and move your finger back toward the tail, you'll feel a prominent dip a short distance past the flank. This is the lumbosacral space and marks the spot where the lumbar vertebrae end and the sacrum starts. The ilium is one of three bones that make up the pelvis. It's shaped roughly like a wing, or the broad, flat section of a moose antler without the spikes, and is the most forward part of the pelvis. Put It To Use • Diagnosis involves ruling out other causes. • Check for clues: less flexible back, lead preferences, activities. • Make tincture of time work for your horse. • Assume a full recovery is possible in most cases. • Weigh hunter's bump involvement. The sacroiliac joint is the junction between the horse's spine at the sacrum ("sacro") and the pelvis at the ilium ("iliac"). The joint is buried under the heavy gluteal muscles of the top of the horse's rump, lying just off the midline on both sides, on a line drawn between the back edge of the tuber sacrale and the spine. It sits at about the highest point of the rump. The tuber sacrale is the bony prominence just behind the flank that is commonly called the "point of the hip," although it has nothing to do with the hip joint. This area has two sets of ligaments, either of which can be damaged and cause pain. The dorsal sacroiliac ligaments run from the tuber sacrale ("point of the hip") over to the top of the sacrum. They don't involve the sacroiliac joint directly, but they do help anchor the ilium to the sacral spine. The ventral sacroiliac ligaments are located deeper, in the area of the sacroiliac joint itself, which they stabilize. This assembly is designed to hold the horse's pelvis tightly to his spine. A normal sacroiliac joint is capable of little movement and contains minimal amounts of joint fluid. Minimize The Chance Of Injury Research has suggested that most pelvic/sacroiliac area injuries occur because of uneven stresses being applied to the pelvis. To minimize this: • Always work the horse an equal amount of time in both directions, at all gaits, and switch leads and diagonals frequently when riding cross-country. • Every two to four weeks, check the horse from the side and directly behind for any evidence of uneven muscling through the gaskin and stifle area, or over the rump. • Be alert for feelings that the horse is not pushing off/using himself as well on one lead or diagonal compared to the other. An attentive rider can pick up this asymmetry before it is evident to the eye as a gait change. • Check the wear of the hind shoes, at farrier visits and at least once between visits, for evidence of uneven shoe wear, compare both right to left and lateral vs. medial on each foot. • Walk the horse on a flat, level surface after trimming to make sure the hind feet are landing perfectly square before reapplying shoes. • Remember that any source of pain in one hind leg will result in overloading of the opposite hind and that a problem with a front leg will also cause overloading of the opposite hind. • Get a veterinarian good with diagnosing hind-end lameness to evaluate the horse at the first sign of any unevenness in shoe wear, muscling or gait. Finding the cause early will save the horse from progressing to a more serious lameness and the host of secondary problems that can result. Causes Of Pain Ligament injuries. Pain in the general area of the sacroiliac may involve injury to the ventral ligaments that stabilize the joint. In some cases, the injury may be an actual subluxation, although this isn't as common as arthritis or ventral ligament strain/damage. The dorsal ligaments running from the tuber sacrale to the sacrum are also often injured, although this injury doesn't necessarily also involve the sacroiliac joint itself. Fractures. Stress fractures along the wing of the ilium have been found in racehorses, both microfractures and those severe enough to show up on X- rays. These fractures are presumed painful. Any of these, alone or in combination, can cause sacroiliac area pain. Problems By having a joint connecting his pelvis to the spine, rather than a solid bridge of bone, the horse gets the benefit of having tissues with a bit more flexibility to them, including some shock-absorbing capacity. However, the sacroiliac joint is mainly an anchor, not designed for much movement. The joint can be overstressed by speed and/or extremes of movement of the hind leg. Racehorses are at risk, as are horses that work with a high degree of hind-end engagement, such as barrel racing, reining, jumping, dressage and horses that work over sharp inclines. Sacroiliac area injury may also occur if the hind leg suddenly slips-as could happen when on mud, ice, pavement and so on-and could even occur on turnout. Diagnosis There are no characteristic symptoms or signs that point to the sacroiliac area as a cause of lameness. A sacroiliac injury would be suspected on a horse with a hind-end lameness that can't be localized to joints or soft tissues lower down the leg, such as when the horse had local anesthetic blocks up to and including the stifle without eliminating the lameness. History may also play a role in making a diagnosis. You would suspect the sacroiliac in a horse that: • Is involved in a high-risk sport/training program or was observed to slip and fall at pasture. • Shows a loss of flexibility through the lower back. • Can only manage a poor bascule over fences, jumps long, refuses jumps, stops in combinations. • Has difficulty with cavaletti. • Demonstrates a loss of impulsion on the flat, is difficult to collect, or "strung out" at the canter. • Obviously prefers one lead and frequently cross-canters. • Shows a reluctance or refusal to work tightly, perform sliding stops or turn on the haunches at speed. In addition, you may note that the horse has: • Hunter's bump or knocked-down hip that is distinguished from an anatomical asymmetry or old injury no longer causing pain. • Uneven muscling, a sore side with less muscle. • Pain on palpation in the area of the tuber sacrale, which suggests either a fracture or involvement of the dorsal sacroiliac ligaments. • An exaggerated sensitivity to palpation over the lower back and sacrum, which may be either a sinking away from the pressure, or tensing and quivering of the muscles (or a good swift cow kick). • Pain at the extremes of range of motion when the leg is pulled back and/or forward. But this is nonspecific and only suggests a possible problem anywhere in the sacro-iliac area, pelvis, hip, even femur. Hunter's Bump Several studies looking at the variations in a horse's anatomy have found that the height of the rump on the two sides at the sacroiliac region may vary by as much as half an inch without any injury/abnormality. It's simply a slight asymmetry of the pelvis. Slight height differences alone can't be used to diagnose sacroiliac-area lameness. Whether these anatomical asymmetries predispose a horse to injury/lameness or influence the gait is unknown, although we wouldn't be surprised if they do. Common terms used to describe changes in the pelvis/sacroiliac area can be confusing, especially if they're not used the same way by everybody. "Hunter's bump" usually means the horse looks higher on one side in the area over the sacroiliac joint, at the highest point on the rump. However, some people call a prominent tuber sacrale (point of hip) a hunter's bump. "Knocked-down hip" usually refers to a horse who has the tuber sacrale on one side appearing to sit lower than on the other. The most common cause of this is a fracture from hitting the bone when going through a doorway. Others will refer to the lower side on a horse that has a hunter's bump as "knocked down." Unless the horse is obviously lame on one side, a careful exam is needed to determine which side is actually the abnormal one, or if it's just an anatomical variation. Diagnostic Options Radiography: X-rays are of limited value both because of the difficulty in obtaining them (horse must be under anesthesia and on his back) and because there may be little to nothing to see in most sacroiliac area injuries. They are most indicated in horses suspected to have a fracture. Scintigraphy ("bone scan"): Although there can be some slight overlap in uptake patterns between horses with sacroiliac-area problems and normal ones, especially in older horses, bone scanning is an accurate way to confirm the diagnosis.