What is the Sacroiliac (SI) Joint?
The sacroiliac (SI) joint is the articulation between the lower part of the ilium (one of the three bones which make up the pelvis) and the sacrum (which is part of the spine). In the horse, the sacrum is made up of five fused vertebrae.
What is the function of the SI?
The function of the SI joint, with the support of the surrounding muscles and ligaments, is to enable the transfer of force from the hindlimb to the thoracolumbar spine. To carry out this function successfully, it needs to provide a stable platform and therefore, the joint does not have the same range of movement as other joints, such as the hock, knee or fetlock for example.
Problems begins to occur when the joint becomes unstable. Unless there has been direct and substantial trauma to the joint, joint instability of the SI is often only minimal. However, this still causes an increase in articular translation within the joint, which can in turn lead to remodeling of the bone, which causes SI pain.
Symptoms of SI pain and/or dysfunction
Equine SI pain and dysfunction is often more prevalent in performance horses compared to those who spend the majority of their time hacking or in low level work. This is not surprising considering their greater workload and the increased demand on the anatomical structures of the body, especially when a high degree of hindlimb engagement is required. Common signs of SI pain and/or disfunction may be poor performance, an unwillingness to go forwards into the contact, reduced engagement of or lameness in the hindlimbs and difficulty in the canter; transitions may be poor or there may be little differentiation between hindlimb movement and foot placement.
Treatment
Physiotherapy intervention can be supportive in reducing SI pain, improving performance and achieving a better quality of life for your horse. It has the potential to treat muscular pain, strengthen structures around the joint and address any muscular or postural imbalances which contribute to the instability. However, if SI issues are suspected, veterinary intervention will initially be required to identify any underlying pathology and provide medical treatment if deemed necessary. This is especially important because pain in the SI region can be a referred pain from other areas of the body, such as the thoracolumbar spine or hindlimbs, as well as be secondary to reduced postural control due to weaknesses in surrounding muscles. Veterinary treatment might be an analgesic injection into the joint to reduce pain in the short term. It is important that the initial, acute pain is addressed as physiotherapy treatment is considered to be effective when the horse is comfortable; it then has the potential to reduce future occurrence of symptoms compared to analgesic treatment alone.
Rehabilitation
Long term goals will be to reduce/prevent the occurrence of any long term pain, restore function and improve performance and quality of life. Therapeutic exercise has been evidenced to be one of the most effective treatments in achieving the above.
Stage 1
In the first stages of rehabilitation, focus is on restoration of pelvic stability. This will be achieved through improving spinal and postural stability. The multifidus muscles have the role of stabilising the intervertebral joints of the spine. Research informs us that the cross sectional area of these muscles within the mid thoracic and lumbar regions of the spine, increase if regular dynamic mobilization exercises are carried out. Such exercises are often referred to as active stretching and include baited stretches. By increasing the strength and cross sectional area of these muscles they become more effective in carrying out their stabilising role and therefore instability, and the injury or degeneration which follows, is reduced. Dynamic mobilization exercises are used in the initial stages of rehabilitation to encourage the horse to flex through the spine and engage the multifidus muscles and abdominal musculature.
Stage 2-a
Once dynamic mobilization exercises have been established, progression to dynamic therapeutic exercise can take place, to further activate the muscles responsible for providing stability. This part of rehabilitation aims to enable the SI joint and lumbopelvic region to maintain stability while in a functional activity. Long reining is a popular exercise for this as it continues to encourage flexion of the thoracolumbar spine whilst the horse is in locomotion. Ground poles are then introduced as they require an increase in limb flexion during the flight phase of the gait. This increased flexion has been shown to increase engagement of the hypaxial and abdominal musculature, which also have a function in stabilising the pelvis and spine. Furthermore, the recorded increase in hindlimb stance phase while the opposite limb is negotiating the pole results in a simultaneous increase in abdominal, hypaxial and gluteal muscle contractions. Therefore, through strengthening the musculature required for improved pelvic, spinal and SI stability, pole work provides effective rehabilitative exercise.
Stage 2-b
Further progression might include changes of rein or circle work. This engages the abdominal muscles alongside another spinal muscle called the longissimus. This is one of the longest muscles in your horse’s body and runs down each side of the spine, above the ribs. By engaging these muscles in this way, lateral flexion of the of the vertebral column is achieved. It is important that this progression follows the dynamic mobilization exercises and initial dynamic therapeutic exercise so that the horse has enough strength to stabilise the spine and pelvis while on the circle.
Stage 3
Longer term prevention and management of the condition includes schooling and functional exercise, with the end goal being the horse returning to, or surpassing, the same level of performance they previously took part in. It is advised that horses take part in work which provides strengthening and conditioning for their discipline. For example, dressage horses might carry out lateral, collection or pole work to encourage spinal flexion and activation of the hypaxial musculature, to support engagement of the hindlimb. Show jumpers might carry out grid work or bounce fences as well as poles and lateral work. Although evidence comes from the human field, it informs us that cross training in this way helps to improve overall fitness, which in turn reduces risk of injury. It is hypothesized that the same can be said for the equine athlete and that a fitter horse will have less risk of SI dysfunction and the related pain. It is important that the veterinary physiotherapist plays a part in the long term management of these horses so that this can be monitored and initial signs detected and managed to reduce the risk of a return in the original symptoms.
Case Study
Bobby is an eleven year old thoroughbred event horse, who I went to see for the first time in October 2022. Although he had recently had his SI joint medicated, his owner was still concerned that his performance in, and willingness towards, his work had not returned. Before visiting Bobby, I contacted his vet to discuss his treatment and rehabilitation. After watching Bobby on the lunge, it was evident that he wasn’t moving comfortably, especially in canter. Further assessment indicated that he was restricted in his hindlimb range of movement, had a number of areas of hypertonicity in epaxial and hindlimb musculature, as well as compensations in his right shoulder and thoracic sling- all of which were making him sore. Although the cause of Bobby's initial pain had been addressed through the veterinary intervention, the compensations which had accumulated during the time he was finding work more difficult remained. He also needed to be reminded of how to use himself and his musculature most effectively and efficiently now his source of discomfort had been addressed.
During our initial session, I treated the areas of hypertonicity, reduced range of movement and discomfort with both manual and electrotherapy, including therapeutic laser over the SI joint. Once I was happy that Bobby was feeling more comfortable, I left his owner with an exercise plan which included both static and dynamic exercises to encourage Bobby to begin using himself more effectively. A month later, I revisited Bobby to evaluate his progress. Not only was he moving more symmetrically and more consistently in all gaits, his muscle tone felt much more relaxed and his passive range of movement had improved. Furthermore, he was back out enjoying his jumping. Although he is clearly on the road to recovery, I have stressed the importance of keeping up with Bobby’s exercises to maintain the structural support in his back and around his SI area to maintain this level of performance – his owner is on top of this and has played a huge part in the success of his rehabilitation plan.
Here's a picture his owner sent me of the two of them enjoying a camp, approximately three weeks after my initial visit.
I asked Bobby's owner if she would give me a quick quote for this blog post and she said:
After having hard ground most of this years event season my TB started to get stiff through his sacroiliac. With Hollys help, providing great treatment and pole work exercise programs, he is a lot more comfortable and I feel like I have my horse back. Roll on 2023 season!
Glossary:
Thoracolumbar spine- part of the spine which is approximately just in front of the withers to the end of the ribs, including the part where the saddle is placed.
Articular translation- movement within a joint
Hypaxial- muscles which lie below the spinal column
Epaxial- muscles which lie above the spinal column
Lateral- movement to the side
Facet joint- point of articulation between two spinal vertebrae
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