Back problems are common among racehorses and can severely inhibit performance, but an accurate diagnosis is often hard to come byThe horse has a strong, well-constructed back, but it is not really designed to carry weight at high speeds, from fast starts, and around turns-especially weight that may move around or sometimes bang down on the back. A horse's back can be injured from stress and strain, as when carrying weight and running at top speed.

Structure of the back
The backbone consists of vertebrae, spinal cord, and branching nerves. The vertebrae come together in a series of joints and are separated from one another by discs that act as shock absorbers. The backbone is somewhat flexible when certain muscles are brought into play.
The vertebrae form a tunnel protecting the spinal cord. The top of each vertebra has a bony extension known as the dorsal spinal process. There are also bony projections out to each side, called transverse processes. The dorsal and transverse processes serve as areas of attachment for the muscles of the back. A strong ligament runs along the dorsal spinous processes, but is absent between the sixth lumbar vertebra and the first sacral vertebra (at the horse's croup)-so this is a relatively weak spot. Because of the strong ligaments and muscles in the horse's back, it is more rigid than the human back, with very little up and down movement and only limited ability to bend from side to side.
The back is an elaborate structure; any one of its components can be injured. A common type of equine back injury is caused by the rider, and a combination of work stress and poor conformation can also lead to problems.
Many back injuries are soft-tissue problems, such as muscle and ligament strains or muscles tying up. Others are bone-related, including fractures of the vertebrae or their dorsal spinous processes. One common problem is a condition where the dorsal spinous processes rub each other and cause chronic pain. Another, called spondylosis, results in formation of new bone on the undersides of the lumbar vertebrae.

Performance compromised
Because the horse continues to perform and is not lame, some types of back injury go undiagnosed. The horse may have "off" days. He may hump up in protest when saddled or seem reluctant to move out freely when mounted. The rider or trainer may notice he isn't happy, but since he continues to perform without obvious lameness, he is kept in training-with a nagging backache.
If the horse continues working, he may eventually become reluctant to run because it hurts him to do so. He may seem stiff and clumsy, and may engage in protest behavior such as bucking, head-shaking, or tail-swishing. Or, he might refuse to back up or bend, resisting any lateral movement.

Difficult diagnosis
The symptoms of a back problem are non-specific and vary from horse to horse. Several possible causes must be considered, and a thorough exam is in order. The fit of the saddle should be checked, and a lameness exam performed. Lower leg problems are not as likely to cause back pain as is lameness in hocks or stifles, but can still be a factor. Foot problems and other chronic sources of pain in the lower leg can result in shortened stride and a "guarded" gait, thus creating tension along the back-which, over time, can develop into a true back problem.
The back should be carefully palpated by a veterinarian. Most horses will dip down a little when pressure is applied in front of the croup, and will hump the back when pressure is applied behind it. A lack of or exaggerated response to this pressure may indicate a problem. Many people think that the horse that sinks down when the back is touched has back pain. But some of these "ticklish" horses are quite normal-the skin is just very sensitive. With severe back pain, a common response to pressure is to arch the back upward, since sinking down usually causes more pain. If pain is severe, the horse may not move at all when pressed, but may groan or show some other indication of long-standing hurt.
Locating the exact area of pain can be helpful in proper diagnosis. A local anesthetic may be injected between the dorsal spinous processes to see if that area is causing the pain. Some clinics have X ray equipment capable of taking radiographs of a horse's back, but it is usually only possible to get side-to-side views, and nearly impossible to take views from above or below.
Many cases of nonspecific back pain are never diagnosed, but clear up after the horse is given prolonged rest. Some horsemen blame back pain on "sore kidneys," but this is unlikely since there is a thick layer of bone and muscle between the horse's outer back and the kidneys. By the time the kidneys would be sore enough to cause pain, the horse would have displayed other obvious signs of kidney disease.
Muscle strain
Muscle strain is the most common back injury and one that usually heals without permanent damage. The strain may occur suddenly after a fall, with a hot, swollen area at the injury site. The horse may stand stiffly, walking with shortened stride in the hind legs. The muscles over the lumbar and sacral regions are most often strained, since that area lacks the extra support of the supraspinous ligament.
Sometimes the cause can be baffling, as when a number of horses at a California racetrack suffered sore backs one season. It was finally determined that the track surface was the culprit; the ground was hard on top and broke away under the horse's hind legs as they ran, straining their backs.
The best treatment for muscle strain is rest and anti-inflammatory medication such as Bute. Massage and hot packs can also help the injured muscles relax.
Slow, careful training can develop the back muscles in young horses and enable those muscles to cope better with the demands of athletic performance. Walking and trotting up gentle slopes is a good way to strengthen a horse's back.

Ligament strain
Strain can also occur in the ligaments attaching the sacrum to the upper pelvis. The strain may be due to sudden injury, but the symptoms may not show up immediately. The horse may become stiff, with decreased impulsion when worked. He may drag his toes or carry his tail to one side. The pelvis on the affected side may appear higher than normal. As with muscle strain, pain can be temporarily relieved with anti-inflammatory drugs, and many of these horses regain soundness after a period of rest.
One of the more common back problems involves strain in the lumbar region right behind the saddle area. In understanding this, it helps to have an idea of how the backbone functions.

How the back works
Like ours, the equine back is made up of several kinds of vertebrae. The dorsal vertebrae, which make up the withers and front part of the back, are linked together in such a way as to have a small amount of sideways and up-and-down movement. By contrast, the lumbar vertebrae (behind the saddle) have more limited movement.
The lumbar vertebrae have long, wide transverse processes, sticking out to the side like outstretched wings. The actual bodies of the vertebrae are joined together by discs of cartilage, but the transverse processes of the last three are joined by special joints with lubricating membranes and ligaments. The joint surface on the back edge of one transverse process joins the front edge of the next, limiting the movement of the backbone in this area.
The joint surface of the last lumbar transverse processes form joints with the corresponding surfaces of the front edge of the sacrum, the final group of vertebrae fused into one bone. The lumbar joints can become inflamed from stress and concussion, resulting in a sore back. Continued exercise only increases the pain.
A horse has either five or six lumbar vertebrae. Some horses with Arabian blood in their backgrounds (including Thoroughbreds) may have the last two lumbar vertebrae wholly or partly fused from birth. This natural fusion may be an advantage because, since there is no movement between those bones, there is less chance of inflammation. Fusion between spinal bones is called spondylosis. Inflammation of the spine is spondylitis. Inflammation of the lumbar vertebrae from strain produces an arthritic condition and subsequent fusion of the vertebrae, thus creating spondylosis.

Healing process
For a long time it was believed that fusion of these joints was a process of aging. It was later discovered, however, that it was instead the result of inflammation and stress creating an arthritis, which in turn produced calcification and bone fusion-in short, a healing process. Inflamed ligaments and acute arthritis in the strained area are painful, but once these joints are fused, there is no more inflammation or pain.
Strain causes many horses to develop fusion of the lumbar vertebrae. The bones of racehorses frequently show these calcifying changes, but the process is not always symmetrical. One pair of transverse processes may be already fused, while the pair on the other side of the same bone may still be moveable, although undergoing active inflammation and pain. Thus, the painful stage might last for some time, even a year or more, until the area is fully healed and calcified.

It takes heart
One English veterinarian, Dr. R. H. Smythe, who studied horse anatomy for 60 years, found that at least half of all racehorse skeletons he examined showed vertebral fusion from inflammation. He believed that the fact so many of those horses continued to run and perform despite sore backs was a tribute to their heart, rather than to their physical perfection. In his opinion, a great many horses, like humans, suffer throughout their lives from varying degrees of backache. Dr. Smythe suspected that many horses that run badly in races are in reality suffering from lumbar inflammation.

Summary
Inflammatory changes are common in domestic horses of all ages, and the subsequent discomfort undoubtedly contributes to variations in performance. During the inflammation stage before the joint is fully calcified (fused), this area will be sore, interfering with the horse's function, and continued stress may keep the problem active for years.
The frequency of equine back problems is hard to pinpoint, since many cases are never diagnosed. The rider or trainer may know a horse has a problem, but there is nothing clearly to blame, as in a lameness situation. Nonetheless, many of these conditions resolve quite well with rest.
Pasture turnout is usually preferable to stall confinement in preventing stiffness and loss of muscle tone. Some cases can be helped with massage, ultrasound, swimming therapy, and anti-inflammatory medications. Localized physical therapies such as a good rub with a heavy towel or use of heat (heat lamps, blankets, liniment), can help, and chiropractic treatment and acupuncture have also given relief in a number of cases.
There is still much to be learned about the causes of back injuries and how to properly diagnose them. Most present day treatment is aimed at relieving the pain and symptoms of reduced performance. If a horse starts to run poorly, time off may be in order to give a strained back time to heal before it is made worse by repeated stress.