The sacroiliac (SI) joint is the point of articulation between the pelvis and the sacrum (lower part of the spine). The joint is supported by several pairs of very strong ligaments and works to transfer the motion generated by the hindlimbs to the rest of the body. As such, it is exposed to high levels of stress during movement but despite being referred to as a joint, it actually has a very small range of motion.

Injuries to the sacroiliac region can be broadly divided into acute and chronic issues. Acute injuries tend to have a traumatic cause such as a slip or fall. Typical signs are moderate to severe hindlimb lameness, with heat, pain and swelling of the area and sometimes hindquarter asymmetry.

Chronic injuries are more common and result from repetitive stress on the SI joint or ligaments. Lameness tends to be mild, may be intermittent and can shift from side to side. Other signs may include back soreness and poor performance with loss of impulsion, reluctance to perform lateral work and unwillingness to work on the bit as well as behaviour changes. Gait abnormalities are sometimes seen, such as a rolling, plaiting or narrow gait but none of these are specific for the condition. Over time muscle wasting can also cause hindlimb asymmetry to develop.

How is it diagnosed?       Because the sacroiliac region lies deep beneath the large hindquarter muscles, the normal techniques we use to diagnose lameness are not as useful.

X-rays are unable to penetrate to the SI joint, and local anaesthetic blocks of this region are difficult; the joint sits very close to the sciatic nerve and if this is inadvertently affected by the local, temporary loss of hindlimb function can result! So often, when history and clinical signs suggest sacroiliac disease, diagnostic tests are used as much to rule out other conditions as to confirm the SI joint as the cause of the problem.

A full lameness examination with flexion tests is essential. Nerve blocks are often required to rule out other conditions that can have similar appearances or could be contributing to the SI pain, such as proximal suspensory desmitis. A rectal ultrasound exam is the only way to visualise the underside of the SI joint where the pathology usually occurs, which may include new bone formation and spurring around the edges of the joint. It also allows assessment of the lumbosacral joint which can be affected concurrently.

Scintigraphy (bone scan) can also yield useful information but the large muscle mass can make interpretation of the scans difficult and sometimes scans can appear normal in horses that do have significant SI joint pathology.

How is it treated?             Acute injuries are generally managed with rest and anti-inflammatories followed by a gradual exercise program to return to work. Treatment of chronic disease includes anti-inflammatories, medication of the region with corticosteroids and again altering the exercise program.

It is important that any other lameness conditions which could be contributing to the sacroiliac pain are also treated. Physiotherapy can be very beneficial and encouraging the horse to work correctly helps to build muscle strength around the SI joint which is essential for successful long term management. For this reason, long breaks from work are usually not recommended for this disease.

In some horses, SI pain requires ongoing management but early diagnosis and appropriate treatment dramatically improves the prognosis. If you are worried about your horse’s performance or they are showing some of the signs described here, get in touch with your vet to discuss your concerns.


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