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Sacroiliac (SI) pain is a common cause of poor performance and low-grade lameness in performance horses. [1] The sacroiliac joint is the point on the horse’s body where the pelvis and the spine connect, playing an important role in their stride.
Damage to the ligaments supporting the region or the sacroiliac joint itself can produce pain and discomfort, resulting in symptoms such as poor-quality gaits, refusing jumps, and “bunny hopping” in the canter.
Sacroiliac pain may result from trauma, repetitive stress, overuse injuries, poor conformation or arthritis. Competition horses involved in dressage and show jumping have the highest risk of this condition.
Treatment typically involves a prolonged rehabilitation period of up to 4 – 6 months. Many horses with SI pain recover and return to performance careers, often at a lower level than their previous level of performance.
Sacroiliac Joint in Horses
The sacroiliac region in horses is the junction between the hind limb and the spinal column. The major components of this region are: [1]
- The sacrum, the fused spinal vertebrae of the sacral region
- The ilium, the sides of the pelvis
- Several ligaments that support these structures
The sacroiliac joint is the connection point between the sacrum and the ilium. The joint has very limited movement capacity due to the supporting ligaments and helps transfer concussive forces from the limbs to the spinal column. [1]
Sacroiliac disease in horses refers to a range of conditions that affect the sacroiliac joint, commonly leading to pain and poor performance. In SI disease, either the joint itself, the ligaments surrounding the joint, or both, are affected. [1][2]
Cause of Sacroiliac Pain
During normal movement, the muscles surrounding the horse’s sacroiliac joint prevent it from overextending or exceeding its physical limits. However, if the muscles of the hind limbs and back fail to prevent overextension, the SI joint may become strained or damaged. [1]
Common causes of SI disease include: [1][2]
- Falling or slipping
- Becoming cast in a stall
- Muscle fatigue from overuse
- Repetitive stress injuries to the muscles due to intensive training
The most common types of SI disease are: [1]
- Damage to the ligaments between the top of the sacrum and the top of the pelvis (dorsal sacral ligaments)
- Damage to the ligaments between the sides of the sacrum and sides of the pelvis (intraosseus sacral and ventral sacral ligaments)
- Arthritis of the sacroiliac joint
Damage to the intraosseus sacral and ventral sacral ligaments can result in luxation or subluxation of the joint, where the bony components of the joint become misaligned. [1]
Risk Factors
The prevalence of sacroiliac disease in racing and competition horses is high. However, many horses show degenerative changes in the SI region without signs of lameness. [3]
Risk factors associated with SI disease include: [3][4]
- Increased body weight
- Dressage and show jumping performance
- Warmblood breeding
- Increased age
- Increased height at the withers
Symptoms
Sacroiliac pain typically causes low-grade lameness or poor performance in competing animals. [1]
Symptoms of SI disease are highly variable, but can include: [1]
- Reduced stride length in the hind limbs
- Changes in the quality and rhythm of the gaits, particularly the walk and canter
- Refusing jumps
- “Bunny hopping” in the canter
- Swapping leads or cross-firing frequently
- Behavioural changes such as rearing, kicking, bucking, or resisting forward movement
Symptoms are usually worse when the horse is ridden as opposed to worked in hand. [5]
Physical changes associated with SI disease include: [1][6]
- Lowering of one hip when viewing the horse from behind
- Asymmetry of the tuber sacrales, the top of the pelvis
- Loss of muscle mass over the croup
- Reduced mobility of the tail
- Asymmetric position of the tail during movement
Traumatic Injury
Horses that experience a traumatic injury to the SI joint may have more severe symptoms, such as: [1]
- Severe hind limb lameness, including non-weight-bearing lameness
- Asymmetry of the tuber sacrales
- Muscle spasms
Horses that develop luxation of the SI joint develop a “hunter’s bump”, a characteristic appearance to the pelvis. [1] In this condition, the tuber sacrales become very prominent.
Diagnosis
Most horses with SI disease present to their veterinarian due to a history of poor performance. As part of the work-up, the veterinarian will perform a lameness examination to determine where the lameness originates from. [1]
From there, additional diagnostics can help confirm the SI joint as the cause of pain. [1]
Flexion Tests
Flexion tests are a technique during lameness examination where the veterinarian will over-flex a limb in order to stress the joints. [1] By doing so, they can emphasize any pain or instability in the flexed joints, allowing them to identify potential sources of lameness.
For horses with SI disease, they may show increased lameness when flexing the hind limbs. However, this result is usually due to overloading of the lower limb to compensate for SI pain causing damage elsewhere, rather than due to the SI disease itself. [1]
Some horses with SI disease may show increased lameness on the limb opposite to the one that is flexed, as having to bear weight on one hind leg may irritate the SI joint. [1] These horses may also refuse to stand quietly during flexion due to the additional pain. [1]
Palpation
Palpating the structures of the sacroiliac region may induce signs of pain in the horse, helping identify the source of lameness. [1]
Rocking the pelvis by manipulating the tuber ischium (front of the pelvis) and tuber coxae (back of the pelvis) can flex the SI joint. [1] This technique can highlight pain within the joint itself.
Pressing on the tuber sacrales can highlight pain in the dorsal sacral ligaments, as these ligaments typically prevent excessive movement of the tuber sacrales. [1]
Some veterinarians may also run a needle cap or pen tip over the croup to encourage the horse to tuck their croup underneath themselves and arch their back (dorsiflexion). Horses that show minimal response to this technique may have SI pain. [1]
A similar test can also trigger lateral flexion of the spine, which can also be reduced in horses with SI pain. [1]
Ultrasound Examination
Due to the thickness of the horse’s hindquarters, X-ray evaluation of the SI joint is usually not possible. Ultrasound examination provides the best method of diagnosing changes in the SI joint, particularly in the ligaments. [1]
There are two main methods of evaluating the sacroiliac ligaments using ultrasound: percutaneous (through the skin) and transrectal (through the rectum).
Percutaneous ultrasound is best for evaluating the dorsal sacral ligaments and how they connect to the tuber sacrales. The veterinarian can evaluate the size of the ligaments and the integrity of the ligament fibers using this technique. [1]
Transrectal ultrasound can allow the veterinarian to evaluate the bony edges of the sacroiliac joint itself, as well as the ventral sacral ligaments. [1][7] Changes such as bone proliferation may indicate arthritis of the SI joint. [1] Changes in size or density of the ventral ligament may indicate inflammation. [7]
Nuclear Scintigraphy
Nuclear scintigraphy is a diagnostic technique available at some referral hospitals and is the gold standard for diagnosing SI disease. [1]
In this procedure, the veterinarian administers a radioactive medication to the horse, which binds to molecules within the bones and soft tissues. Areas of increased or decreased blood flow or increased activity of the bone-producing cells (osteoblasts) bind more radioactive particles than normal tissue. [1]
Two to four hours after injecting the medication, the veterinarian uses a special camera that identifies areas of radioactivity. Areas showing “hot spots” of radioactivity are likely to cause pain or lameness. [1]
Structures of the SI region evaluated using this technique can include: [1]
- Sacrum
- Tuber sacrales
- Ilium of the pelvis
- Dorsal sacral ligaments
- Sacroiliac joints
- Muscles of the spinal column
Treatment
Treating sacroiliac disease requires intensive management by owners. A combination of stall rest, slow rehabilitation, and joint injections may be necessary to manage SI disease. [1]
Stall Rest
Most horses require around 2 months of stall rest after being diagnosed with SI disease. The goal is to prevent all unnecessary movement of the sacroiliac region, to allow the sacral ligaments to rest. [1]
Typically, only hand-walking for 10-15 minutes, 2-3 times a day is permitted during the stall rest period. Most horses also receive anti-inflammatory medications, such as phenylbutazone, to reduce pain and help control the inflammation within the sacral ligaments. [1]
Rehabilitation
Rehabilitation protocols for sacroiliac pain aim to slowly increase the workload of the sacroiliac region, while increasing the strength of the surrounding musculature. The main focus is strengthening the muscles of the spinal column and the croup, which help stabilize the sacroiliac region. [1]
Rehabilitation typically begins with 1-4 months of walking under saddle or in-hand, moving in serpentines and circles. Turning and circling improves the lateral flexion of the spine and encourages gentle rotation of the sacroiliac joints. [1]
As the horse gains strength, the diameter of the circles and turns is reduced to increase the amount of lateral flexion and rotation. Circling and turning at the trot is added to the protocol after several months of walking. [1][8]
Finally, horses can canter under saddle for short periods, slowly increasing in duration until normal performance returns. [8] Downward transitions from canter to trot are a crucial component of rehabilitation, as this motion flexes the sacroiliac region significantly and can build strength. [1]
In most cases of sacroiliac disease, the total rehabilitation time is 4-6 months. Horses require re-evaluation, including repeat ultrasound, every two months during the rehabilitation process to help guide activity levels. [1]
Joint Injections
For horses with disease affecting the sacroiliac joint itself, injecting the joint with corticosteroids and/or hyaluronic acid can help reduce inflammation and slow the progression of arthritis. [1][9]
Injecting the sacroiliac joint is difficult due to its location beneath the ilium of the pelvis. Generally, the veterinarian’s goal is to deposit the corticosteroid close to the joint so that the medication diffuses into the affected area, rather than injecting the joint itself. [1]
SI injections involve a straight, 20-25 cm long needle inserted into the back, just above the sacroiliac joint. Some veterinarians may use ultrasound to help guide placement of the needle to ensure maximum efficacy. [1]
Other Treatment Modalities
Platelet-Rich Plasma
Platelet-rich plasma is a technique where plasma from the horse’s own blood is injected into a site of tissue damage. Platelet-rich plasma contains high levels of cytokines, which are signaling molecules that encourage healing and tissue repair. [1]
Horses treated with platelet-rich plasma often show faster healing and more complete healing of damaged sacral ligaments. However, the rehabilitation process can still take up to 4-6 months, despite improved ligament healing. [1]
Sarapin
Sarapin is a pain control agent derived from the pitcher plant. The exact mode of action is unknown, but the compound has been successfully used for chronic neuromuscular pain in humans. [10]
Some veterinarians use sarapin as local injection into the sacroiliac region to reduce pain as part of their treatment protocols for SI pain. However, there is currently no evidence to support the efficacy of sarapin as a treatment protocol in horses. [10][11]
Mesotherapy
Mesotherapy is a method where the nerve fibers in the skin are stimulated to inhibit the transmission of pain in the spinal cord. There is limited evidence of its efficacy in horses, however the technique is currently used for chronic pain in humans. [10]
To perform mesotherapy, the veterinarian uses a multi-injection device to deliver multiple small doses of medication into the muscles along the spinal column. Typically, the medications given are steroids, local anesthetics, muscle relaxants, or sarapin. [10]
Muscle Relaxants
Muscle relaxants such as methocarbamol may benefit horses with SI disease, particularly if they are experiencing muscle spasms due to pain. [10]
Prognosis
Studies show significant variation in the prognosis of SI disease cases, ranging from 15% to 90% of horses returning to their previous performance level. [11][12] Overall, veterinarians consider the prognosis of SI disease guarded for long-term performance. [1]
One study showed that around 32% of horses return to performance at a lower level than before their diagnosis. Only 13% of the horses in this study were still performing at their previous level at 1 year after rehabilitation. [12]
Summary
- Sacroiliac pain is most common in racing and competition horses, particularly dressage horses and show ju