For unknown reasons horse ailments seem to go in fashionable cycles. Proximal suspensory disease, gastric ulcers and kissing spines have all been ‘in’ in the last couple of years but the top problem for 2013 would seem to be sacroiliac disease. I suspect that people hear about their friend’s horse being diagnosed with something, realise that their horse isn’t going right, ask the vet to look for the ailment that the friend’s horse had and voila – there is evidence that their horse has the same problem. I think that internet forums are responsible for this to some degree too as people necessarily reply to the ‘my horse isn’t quite right’ posts with advice gleaned from their experiences with their own horses. A lot of horses will have low level problems with some or all of the above conditions and if you go specifically looking for something you often find it.
What and where is the SI joint?
The sacroiliac joint is formed between the wings of the pelvis and the sacrum (the lower part of the spine). You can palpate it on your own back roughly where the two hard ‘knobbles’ are to either side of your lower spine. In the horse the joint plays an important part in transferring the propulsive forces generated by the hindlegs to the rest of the horse’s body. The joint is stabilised by several strong ligaments which help to attach the pelvis to the rest of the body.
Types of SI injury
Acute injury may occur as the result of a fall causing rotation or fracture of the pelvis. In chronic disease caused by arthritic changes to the joint or ligament damage it is more common to have a history of poor performance, poor hindleg impulsion and poor or asymmetrical hindquarter muscling. A gradual and progressive loss of performance is usual and it is generally fairly non-specific.
Anything that makes the horse move incorrectly behind – eg. suspensory desmitis or hock spavin – can place a strain on the SI joint and cause eventual damage to the joint and ligaments. This is a secondary disease process and the SI will not improve until the primary problem is addressed.
Some horses react to pressure in the relevant area and sometimes muscle spasm can be apparent on palpation. It is a tricky part of the horse to view diagnostically as there is deep surrounding muscle coverage. For this reason radiography is rarely possible. Ultrasound can be quite useful, especially if there is ligament damage. Scintigraphy is often used (see previous article on Diagnostic Imaging here) as it gives an idea of active disease processes: if there is abnormal, increased or asymmetric uptake in the SI area it is indicative of disease. This may still however be secondary and compensatory as a result of other causes of hindlimb lameness.Diagnostic analgesia (‘joint-blocking’) is very useful but quite tricky to carry out, agai because of the quantity of overlying muscle. It is not as precise as some of the lower limb blocks and other causes of lameness must be addressed first, but a significant improvement in the horse’s way of going after blocking the SI joint is usually diagnostic for SI disease.
Usually a combination of techniques are needed to reach a diagnosis – a detailed history; thorough examination of the horse in-hand, lunged and under saddle; scintigraphy and blocking.
Treating any other sources of hindlimb lameness as a priority is key. Once that has been addressed, or in the cases of primary SI disease, then treatment usually consists of an initial period of rest and anti-inflammatories followed by targeted physiotherapy. Warming up the muscles in the area thoroughly before work is recommended (massage may help with this) and long-reining and work under saddle in a long low frame both help. This can progress to work over poles to engage the hindlimbs and raised poles are particularly helpful. Careful lateral work encouraging the hindlimbs to step under and across can be beneficial as can slow hillwork on a diagonal gradient. A controlled and progressive programme of exercise is vital.
The joint can be medicated with steroids and other anti-inflammatory drugs. This is quite difficult to perform but can be useful for some horses. It may needed to be regularly repeated however and drug withdrawal times may be an issue in competition horses.
Equidronate (the new name for Tildren) is not licensed for SI disease but does seem to have some positive effects. It is a bisphosphonate drug which normalises bone metabolism and prevents further resorption in areas of disease. It is given as an intravenous drip over a short time period and horses need to be monitored during and after infusion as there is a small risk of colic. This treatment must still be combined with correct physio and strengthening work to be effective.
SI disease is a frustrating disease to diagnose and treat. Early diagnosis and treatment is most likely to be associated with a favourable outcome. Most horses can return to their previous level of work, however if it exists in combination with other hindlimb lameness issues then the prognosis becomes less favourable.
Scintigraphy image courtesy of Rainbow Equine Clinic