Structure and function

The sacroiliac joint (SI) is the only bony connection between the horse’s hindlimb and the vertebral column. The joint is composed of two major bones: the wing of the ilium, part of the pelvis, and the wing of the sacrum, part of the spine. Two SI joints sit on either side of the spine. The joints’ main function is to connect the hind limbs to the rest of the skeleton with minimal movement in the joint itself. It transfers forces from the hindlimb during weight bearing through to the vertebral column. The ligaments and muscles surrounding the joint play an essential role in supporting the joint.

SI dysfunction

Pain or injury in the SI has two main causes: primary sacroiliac injury which is caused by direct trauma to the area, e.g., rotational falls leading to acute ligament injury or fracture to the associated bone. The second and more prevalent cause is SI discomfort secondarily to issues in the lower hind limb, such as proximal hindlimb suspensory or hock arthritis. Any form of instability in the joint can cause bony changes and degeneration over time. If SI pain is left undiagnosed or not treated, the surrounding muscles supporting the joint begin to waste, mainly the gluteal muscles causing further instability and discomfort. Long-term muscle loss increases the prominence of the tuber sacral, commonly referred to as hunter or jumper’s bump.

Signs of SI dysfunction

Common signs of SI dysfunction include regression in performance and changes in behaviour. The most prevalent signs are exacerbated at canter where horses become disunited behind and struggle to engage their hind limbs displaying a shortened bunny-hopping gait. Riders also report difficulty during lateral work with these cases.

Treatment

Initial treatment will be determined by the horse’s vet after assessment. Steroid injections or conservative management and rest are the most common forms of treatment. If SI pain is secondary to lower hindlimb pathologies these will also require intervention. Following initial treatment from the vet the physiotherapist will begin the horse’s rehab to support conjunctive treatment.

How can physiotherapy help?

The primary aim of the physiotherapist will be to reduce pain and improve comfort. Physios will work to improve comfort with the use of non-invasive electrotherapy machines, e.g., Pulsed Electromagnetic Field Therapy. Manual therapies such as massage and myofascial release will help release any tension or spasm in the surrounding musculature. Heat may also be prescribed as part of a home rehabilitation program to help relieve muscle tension and maintain circulation to the area.

Once initial discomfort is under control, long term, restoring and increasing muscular and ligament support around the SI is essential for pain management and preventing further instability. To achieve this, muscles of the core, hindlimbs and back must be strengthened. This can be achieved through a series of rehabilitation and strengthening exercises followed by correct ridden work.

Some exercises which are commonly used in rehabilitation plans for SI pain include but are not limited to: hindlimb weight shifting, baited stretches, pole work, backing up, lunging aids, pelvic rounding, core strengthening exercises, water treadmill therapy and targeted ridden work.

These exercises aim to increase core engagement, encourage hind limb propulsion thus encouraging symmetrical muscle development around the SI offering support and stability to the joint. Rehabilitation time will vary case to case depending on the degree of instability, muscle loss and treatment of any other concurring issues. If SI dysfunction is treated and rehabilitated correctly horses stand a fair chance of returning to previous levels of performance.