The sacroiliac joint in horses; the key to forward movement
The sacroiliac joint is one of the most important parts of a horse's body and perhaps at the same time, one of the least known.
This joint and its related structures form the connection between the horse's pelvis and spine.
Its function is to enable the transfer of force from the horse's powerful hind legs to the pelvis and then to the spine.
The result of this process is the horse's very important forward movement.
However, the sacroiliac joint differs from other joints, such as fetlocks or hocks; among other things, this joint itself has a relatively limited range of motion, lacks a distinct joint capsule, has very little associated synovial fluid, and is composed of two different types of cartilage.
The stability of this joint is provided through a complex ligamentous structure and associated muscles.
Unfortunately, evaluating this important and complex joint is very difficult.
Due to its location deep within the pelvis and its protection by thick muscles and fatty tissue, the sacroiliac joint in a horse is neither visible nor easily palpable or manually examinable.
The size and density of this part of the horse's body make standard radiography difficult, and ultrasound imaging can also be challenging.
Clinical complaints and potential signs of sacroiliac problems may also result from a large number of other issues and conditions in the horse.
As a result, identifying and accurately diagnosing sacroiliac problems in horses is a serious challenge for horse owners and their veterinarians.
However, understanding the importance of the sacroiliac joint for the horse's basic movement and recognizing the early signs of problems are the first steps toward diagnosis and mapping out a path to recovery.
Potential signs of sacroiliac problems All the movements we expect from sport horses require an efficient sacroiliac joint.
These include fast running, sudden stops and sharp turns, jumping, lead changes, and gymnastic movements.
Problems or disorders of the sacroiliac joint can lead to a range of vague movement-related issues.
Riders often say they feel the problem without it being seen as a real "lameness" when observing the horse's movement.
These signs may include the following: a newly developed and increasing reluctance to work, along with a loss of natural forward movement or propulsion.
Resistance to collection or rounding of the back.
Stiffness and rigidity, especially when transitioning between gaits.
Additionally, affected horses may have difficulty with lead changes, refuse to jump obstacles, or even start bucking and kicking.
Other signs include: mild dragging of one or both hind limbs on the ground.
Asymmetry in the hindquarters or unequal pelvic movement and uneven muscle development in longer-term cases.
Abnormal tail carriage or unequal placement of hind hoof prints, especially on a circle.
Changes in smooth and rhythmic canter.
"Rabbit-like" movement of the hind legs.
It is also always recommended to ask the farrier if they have noticed any subtle and imperceptible changes in the horse's behavior during shoeing.
Sometimes very early changes in the sacroiliac joint are noticed by the farrier; for example, the horse may not move easily when asked to step sideways while tied in cross-ties.
It may also be that when the farrier lifts and moves a hind leg, the horse has more difficulty maintaining balance on the opposite hind leg.
Since sacroiliac issues can be subtle and their definitive diagnosis can be challenging, all these seemingly minor complaints should be considered important.
If any of these signs are observed, it is reasonable to suggest the possibility of a sacroiliac problem.
However, because these symptoms can also be caused by several other conditions, it is important for affected horses to undergo a complete clinical examination and thorough history review.
All movements required of sport horses need a healthy and functional sacroiliac joint.
These movements include running at speed, sudden stops and sharp turns, jumping, lead changes, and gymnastic movements.
Diagnosing sacroiliac problems A category of sacroiliac problems can be classified as acute cases.
Acute or very recent onset of clinical signs related to the sacroiliac is most likely associated with trauma.
Slipping on a wet or uneven surface, falling during movement and play in the pasture or during competition, kicking, or other powerful movements can all damage the ligaments and muscles that support the sacroiliac joint.
If the trauma is severe enough, the joint surface itself may also be involved.
Taking a detailed history, with special attention to the timeline of the onset of the condition, can often reveal a likely traumatic event as an underlying factor.
Another category of sacroiliac problems involves a more chronic, subtle, and gradually progressing form.
Dr. Sue Dyson from the Animal Health Trust's Equine Studies Centre, Newmarket, UK, published a review in 2010 of 74 horses with confirmed sacroiliac pain in the Equine Veterinary Journal.
Her findings showed that dressage and show jumping horses were more at risk of sacroiliac problems compared to horses used in other disciplines.
Additionally, older, larger, and heavier horses also had a higher share in this group; a point that indicates inflammation from "gradual wear and tear" and the pressure on the sacroiliac joint from long-term use and the physical demands of a large and heavy build have led to more problems.
It was not surprising that warmblood horses constituted a higher proportion, equivalent to 51 percent, of the affected horses compared to other breeds.
Another important point in Dr. Dyson's study was that sacroiliac joint pain was seen alone in only 47 percent of the horses in her study group.
Many horses had other problems or conditions in other areas of the body that were thought to contribute to their sacroiliac issues.
Weakness, incoordination, or pain in other joints, muscles, ligaments, or tendons gradually affect the horse's movement.
Due to its location and function, the sacroiliac joint is under more pressure when the horse tries to compensate for such issues.
Dr. Randy Eggleston, a clinical professor and surgeon in the Department of Large Animal Medicine, Surgery, and Lameness Services at the University of Georgia College of Veterinary Medicine, also believes that many sacroiliac problems stem from other issues in the horse's body.
Dr. Egleston said: "Although the sacroiliac joint has attracted much more attention in recent years and has almost become a common and 'trendy' diagnosis, most suspected sacroiliac cases seen in our hospital actually have problems in other areas.
"Sacroiliac problems can be subtle, and a definitive diagnosis can be difficult.
These symptoms may also be caused by several other conditions; therefore, it is important for horses suspected of sacroiliac pain to undergo a complete clinical examination and thorough history review.
©Amy K.
According to Dr. Egleston, all these potential problems should first be carefully evaluated clinically, and addressing these issues often leads to the elimination of sacroiliac pain.
(See the section "Underlying Conditions Affecting Sacroiliac Problems" below.)
If no other physical problem is found in the clinical examination, the possibility of a primary sacroiliac condition should be considered, and then other specific diagnostic tests should be conducted.
Ultrasound of the sacroiliac joint is the most common diagnostic method used and can show evidence of degenerative joint disease (arthritis) or indicate the presence of scar tissue and damage in the supporting soft tissue structures.
In large and muscular horses, due to the thickness of this area, scanning can be challenging.
Transrectal ultrasound, where the ultrasound probe is inserted through the rectum, just like when ultrasound is performed to diagnose mare pregnancy, can provide another additional view of the ventral (lower) surface of the sacroiliac joint and sometimes offer more information.
Radiography of the pelvis and sacroiliac area of the horse is particularly difficult, both due to the size of this area and its thickness.
Ordinary radiography of the pelvis should be performed when the horse is anesthetized and laid on its back.
This position sometimes allows for obtaining an image that may provide useful information, but due to the complex anatomical structure of the horse's pelvis, it is not always successful.
Many veterinarians sometimes have little inclination to perform radiography in these cases because inducing anesthesia and waking up again is stressful for the horse.
This stress can be particularly challenging for horses that may already have pelvic instability and problems in the sacroiliac joints.
Thermography or infrared imaging can be useful in identifying areas of inflammation or overuse in the sacroiliac area.
Scanning the horse, then working the horse, and scanning it again is especially helpful.
This dynamic thermography can show the 'before and after' changes in blood flow and heat in a specific sacroiliac area and help confirm the diagnosis of sacroiliac injury.
Dynamic diagnostic capabilities, or methods that can show the current physiological status of structures, are very important in confirming sacroiliac injuries, because as Dr. Egleston explained: "We may see changes in the sacroiliac joint or surrounding structures with ultrasound and even radiography, but this does not prove that those changes are significant in that particular horse or play any role in the horse's pain and lameness."
Many horses may show old and inactive injuries or other chronic changes that are not related to the current condition of that horse.
This thermography scan shows the back of a horse with sacroiliac pain.
The horse's head is facing away from the thermograph.
The thermography scan scale is seen on the right side of the image and shows a color gradient from black (cold) to white (hot).
The closer the colors are to the top of the scale, the higher the temperature.
Temperature results from blood flow, muscle activity, inflammation, and other factors.
In this scan, the base of the tail in the center of the image is hot and white.
This is normal because rectal heat is present under the tail area.
This horse also shows increased heat over the left sacroiliac area and gluteal region.
Thanks to Kent Marcella, DVM 2.
This thermography scan of the sacroiliac area is the same horse in photo 1 after exercise.
The left gluteal region and sacroiliac area showed more heat compared to the pre-exercise scan (photo 1).
Other parts of the horse's body also show increased heat due to increased blood flow and muscle activity from exercise, but the changes in the sacroiliac area and left gluteal region are more significant.
This "dynamic" thermography (comparing pre- and post-exercise scans) allows the veterinarian to more confidently conclude that this horse's problems are actively related to its sacroiliac joint area.
Thanks to Kent Marcella, DVM Nuclear scintigraphy is another dynamic method that can provide evidence that the sacroiliac joint is currently truly inflamed and irritated.
A substance with a nuclear marker is injected into the horse.
This substance circulates throughout the horse's body and is only absorbed or concentrated in areas where damage has occurred and the repair process is underway.
Then a specialized scan of the body is performed, and the nuclear material that has settled in these active areas is seen as "hot spots" or areas of concentration.
This shows the veterinarian which active areas are directly related to the current problem of the same horse.
Research is also currently underway to develop the possibility of performing a full-body CT scan on a standing and sedated horse.
This technology could dramatically improve the way sacroiliac joint problems are diagnosed and allow veterinarians to image the joint itself with minimal risk to the horse and also assess its soft tissue connections.
Although this technology is not yet available, these devices have been built and are actively being tested and refined in clinical settings.
Treatment of sacroiliac joint problems Once the diagnosis of a sacroiliac joint problem is confirmed, there are several treatment options for your horse.
This joint, like any other joint, can be injected with anti-inflammatory drugs.
The purpose of this medication is to reduce inflammation and pain in that area.
These injections can be used in conjunction with muscle relaxants and other systemic anti-inflammatory drugs to help the horse move more comfortably and correctly.
Although most horses are rested from heavy work and competition during the recovery period, controlled physiotherapy remains very important.
Horses are trained according to a very specific program designed to increase the mobility of the supporting structures of the sacroiliac area and help strengthen the stabilizing muscles of the joint.
Acupuncture, pulsed electromagnetic energy, laser therapy, and ultrasound are all used to help reduce tension and spasms in the sacroiliac area during the recovery period.
Once the diagnosis of a sacroiliac joint problem is confirmed, there are several treatment options available for your horse.
To help reduce tension and spasms in the sacroiliac area during the recovery period, acupuncture, laser therapy, and ultrasound are used.
Research shows that horses with primary sacroiliac joint injuries require more time to recover and often do not return to full athletic performance.
However, horses whose sacroiliac joint strain is caused by other issues can perform very well once joint pain, ligament strain, hoof imbalance, or improper riding pressure is resolved.
Understanding the sacroiliac joint and its impact on the horse's basic movement, as well as recognizing the early signs of a problem, are important steps in reaching a diagnosis and mapping out a path to a healthy sacroiliac joint.
Underlying conditions affecting sacroiliac issues, due to the location and function of this joint, mean that when the horse tries to compensate for other problems, the sacroiliac joint is under more pressure.
In cases where sacroiliac pain is suspected, taking a detailed history helps identify known risk factors.
Additionally, a thorough physical examination will help rule out joint inflammation, hoof balance issues, back conditions, and other potential contributing factors.
This is a lateral radiograph of a normal hind hoof showing the natural angle of the pedal bone, or P3.
P3 is the third phalanx and the main bone inside the hoof.
The green arrows indicate the angle this bone should have.
The tip of the bone is slightly lower than the heel.
This position allows for balanced standing and the ability to push off from the toe in forward movement.
This is a lateral radiograph of a hind hoof of a horse with a negative palmar angle.
The tip of P3 is positioned higher than the back of the bone.
This is indicated by the height difference of the red arrows.
Instead of the normal 2 to 7-degree angle, this arrangement creates a negative angle.
This horse does not have proper balance and places more weight on the heels.
This body condition leads to increased pressure and tension on multiple structures, from the hind suspensory ligaments to the hamstrings, the sacroiliac joint, and the lower back.
This condition is often seen in warmblood horses, and these breeds also have a higher incidence of sacroiliac issues.
Horses suspected of having sacroiliac problems should be carefully evaluated for the following: hock joint arthritis can cause horses to hesitate in changing gait, be unable to arch their back well, and have restricted forward movement.
Desmitis of the upper suspensory ligament (inflammation of the fibrous ligament near the upper part of the cannon bone, which can range from mild to severe), especially in the hind legs, can create symptoms similar to hock joint arthritis.
Overlapping of the dorsal spinous processes or "kissing spines" can cause back pain in the horse, disrupt forward movement, and manifest as behavioral reactions; ranging from mild reluctance to work to complete refusal to move forward under saddle and bucking.
Negative palmar angle in the heel area is relatively common in warmblood horses.
The pedal or P3 bone is located inside the horse's hoof.
It is generally said that the underside of this bone should have an angle between 2 to 7 degrees relative to the ground.
This condition creates an angle that allows the toe to be slightly downward and provides the horse with optimal balance and suitable propulsion force from the limbs, especially the hind legs.
In horses with a flat to negative palmar angle, the P3 bone is positioned higher at the anterior edge, meaning the toe, and lower at the posterior edge, meaning the heel.
These horses practically stand and move in a "sitting back" position; a condition that puts more pressure on the hind leg, including the upper suspensory ligaments, hamstring muscles, and gluteal muscles, as well as on the sacroiliac joint area.
About Kent E.
Marcella, veterinarian Thanks to Kent Marcella, veterinarian Kent E.
Marcella, veterinarian, is a graduate of the New York State College of Veterinary Medicine at Cornell University.
He has treated sport horses in all disciplines and levels, including horses participating in international competitions, for over 30 years.
Marcella has served as an official veterinary authority at many events worldwide, including national championships, world championships, and the Olympic Games.
He holds a specialist certification in thermal imaging and is currently a board member of the American Academy of Thermology.
Marcella, who earned a bachelor's degree in English from Dartmouth College, has also written articles for numerous publications.
This article was first published in the Summer 2024 issue of Practical Horseman.
Source: Practical Horseman – Health