By Lorre Mueller, equine osteopath, MMCP
Member of Veterinary Compendium Content Advisor group
Some practitioners believe that there is no motion at the equine sacroiliac joints. That is simply not true – there IS motion at these joints.
Of course, the sacroiliac joints do not function independently but are part of a complex, dynamic, whole-body system. More on that later.
First, some anatomy…
Sacroiliac (SI) joints are synovial joints located between the sacrum and the ilium of the pelvis. They are very strong, stabilizing joints.
There are two types of cartilage within these joints: fibrocartilage covers the joint surface of the ilium and hyaline cartilage covers the joint surface of the sacrum.
The sacrum’s stability comes from four very strong ligaments that hold the sacrum to the pelvis:
- dorsal sacroiliac ligament
- interosseous ligament
- ventral sacroiliac ligament
- sacrosciatic ligament
Sacroiliac joint motion
The horse’s hind limbs generate huge propulsive forces that are transmitted through the wings of the ilium, pushing against the base of the sacrum – through the SI joints – and onward through the lumbar spine, resulting in forward propulsion.
Because the SI joints are located deep within the pelvis and beneath thick gluteal musculature, it is impossible to directly palpate SI joint motion. However, SI joint motion can be assessed by applying focused manual forces to the tuber sacrale or tuber coxea. It is also possible to visualize SI joint and ligament disease with a transrectal ultrasound and CT imaging in select hospitals with larger gantry sizes (i.e., opening for patients).
An in vitro equine study showed the following motions at the SI joints (Haussler 2009). These motions were measured on cadavers with the ligamentous system of the SI joints intact, and then cut to see how much more motion could be produced.
- Axial rotation: 2° on each side
- Lateral bending: 1° on each side
- Flexion (counternutation): 1°
- Extension (nutation): 1°
Another equine study measured SI joint motion in vivo at the walk versus the trot using both pin-mounted and skin-mounted sensors (Goff 2010). The following are the pin-mounted values:
- Lateral bending: 1.64° at the walk or +/- 0.2° more than occurred at the trot
- Flexion-extension: 3.45° at the walk or +/- 0.2° more than occurred at the trot
- Axial rotation: 5.0° at the walk or +/- 0.4° more than occurred at the trot
Although these motions are small, they do exist, so the answer to our question is: Yes, there is motion at the SI joints. In short, it is misleading (1) to completely disregard the fact that there is motion at the SI joints and (2) to not provide the public with a clear understanding of all the other, larger-amplitude joint motions that occur within the sacropelvic region.
Now let’s look briefly at pain and dysfunction.
Sacroiliac joint pain and dysfunction
What is pain and nociception?
Nociception involves sensory information arising from a noxious stimulus within tissue of the body. The sensory information from nociceptors in the tissues is sent to the spinal cord and on to the brain where it is interpreted as pain. Pain can be influenced by social, physiological and psychological factors.
Acute pain acts as an alert to an injury (e.g., touching a hot stove) or to prevent further damage to tissue (injury, inflammation). Inflammation is a biological process designed to help heal tissue injuries.
Chronic pain, like chronic inflammation, can persist long past the initial injury and associated healing process. When this happens, this can become dis-ease, creating more complex problems because of the body’s more regional or systemic responses, which makes it much more challenging to locate the initial source of pain or injury.
What is dysfunction?
In the simplest terms, dysfunction is impaired or abnormal function. There can be dysfunction in any system of the body – circulatory, visceral, muscle, fascia, nerves, and so forth. Sometimes the dysfunction has been in place for so long that it has cascaded into several different body systems, again making it difficult to locate the initial source of pain or dysfunction, especially in animals who cannot tell us where it hurts. Even with humans who are able to tell us where the pain is felt, we know that the source can often be far from the described site of the pain or discomfort.
Locating the source of pain or dysfunction
Because there are no isolated motions within the sacropelvic region – any motion within one joint also induces three-dimensional movements in all surrounding articulations –, it is often difficult to determine the exact source of equine back or pelvic pain or dysfunction. Is it…
- the SI joint?
- the lumbosacral junction?
- the lumbar or lumbosacral intertransverse joints?
- the coxofemoral joints?
- a hind limb lameness?
- or any combination of the above?
Here are some clinical signs that might indicate that the horse has SI joint dysfunction and/or pain… always remembering that the motion within this region is not isolated to only the SI joint:
- Back pain
- Poor performance
- Behavioral changes
- Difficulty with the canter
- Difficulty with lead changes
- Cross cantering
- Hind limb lameness
- Difficulty engaging the hind limbs
In a group of 296 horses with sacroiliac regional pain, 15% of the horses had localized pain in the sacroiliac region, whereas 85% had concurrent pain sources in addition to the sacroiliac region (Barstow 2015). Those concurrent pain sources included:
- Hindlimb lameness: 38%
- Fore- and hind limb lameness: 24%
- Thoracolumbar pain and limb lameness: 21%
- Thoracolumbar pain: 11%
- Forelimb lameness: 5%
This study demonstrates how important it is to examine all possible contributing factors and body regions. We cannot point to only one area of the body for pain, immobility, and dysfunction – we need to broaden our focus to a whole-horse perspective.
Assessing and treating pain and dysfunction
The purpose of this Science Bite is to answer the question about motion in the SI joints. The assessment and treatment of SI joint pain and dysfunction is a different discussion with many parameters to consider. In the meantime, here are some questions to ponder – no matter what your training or scope of practice.
- Are we looking at the horse as a whole?
- Have we obtained a comprehensive history of the horse from the owner, rider, trainer, or anyone else involved with the horse who could provide helpful pieces to the puzzle?
- Have we done a thorough inspection of the horse?
- Have we watched the horse move (at all gaits, in both directions, with and without a rider)?
- Has a thorough physical examination been performed?
- Has diagnostic imaging been done? Will radiographs or ultrasound be helpful or do we need other advanced imaging?
- What is the diagnosis (assessment of the problem)?
- What is the treatment plan, based on all the information gathered above?
- Who will be involved in the treatment and support plan? Veterinarian? Physiotherapist? Osteopath? Bodyworker? Farrier? Saddle fitter? Trainer?
- What is the prognosis (prediction of the progression of the disease or problem)?
- How will we measure our success (outcome measures)? Have we made improvements or made the situation worse?
- What does the follow-up look like?
- Depending on the answers to the above questions, do we recommend continuing the treatment plan or changing direction, re-evaluating, and possibly developing a new treatment plan?