Sacroiliac (SI) joint region pain is common in sport horses and generally results in poor performance, with a horse’s gait being substantially worse when ridden than when working in hand or longeing, especially in canter. Affected horses typically struggle to establish canter, buck either in the transition or in canter, kick out, show limited hind-limb impulsion, and might spontaneously break to trot.

Ideally, veterinarians diagnose sacroiliac joint region pain by eliminating other potential sources of pain and assessing the horse’s response to diagnostic anesthesia (nerve blocking) because horses might improve substantially with blocking despite failing to respond to local joint treatment. However, some clinicians base their diagnosis on clinical findings and the horse’s response to systemic and injected medication.

Researchers for the Animal Health Trust, Centre for Equine Studies in Suffolk, U.K., invited veterinarians who had performed at least one sacroiliac joint injection, whether for diagnostic (with local anesthetic), therapeutic (with medication), or combined purposes (simultaneous local anesthetic and medication concurrently), to complete a questionnaire about their experience. Of the 212 respondents, 110 performed diagnostic, 187 therapeutic, and 49 combined injections. The veterinarians were asked to record the injection technique, volume of injected material and substance used, and the type of complications seen following anesthesia, medications, and combined injections, respectively, in the SI joint region.

Researchers assessed associations between complications described in the questionnaire and the clinicians’ experience, technique, volume, and substance through binary logic regression. Most clinicians used a cranial contralateral blind approach for diagnostic and combined injections, while they used a cranial ipsilateral approach for therapeutic injections. Approximately half the clinicians used ultrasound guidance for diagnostic and combined injections, and 63% of them used it for therapeutic injections. More clinicians sedated horses routinely for therapeutic and combined injections than for diagnostic injections.

Only half the clinicians injected both the left and right sacroiliac joint regions when performing diagnostic injections, while many injected both for therapeutic and combined injections. The local anesthetic solution veterinarians used most was mepivacaine for both diagnostic and combined injections. Corticosteroids were the most commonly used substances for therapeutic and combined injections, and pitcher plant extract was used for therapeutic injections in some cases.

After each of the three procedures, the most common complications were hind-limb weakness and ataxia (incoordination), followed by recumbency (inability to rise from lying down). Clinicians reported each complication more after diagnostic anesthesia alone than with treatment or combined injections. Other complications veterinarians reported included sciatic, femoral, or obturator nerve dysfunction, shivering and stringhalt-like behavior, patchy sweating, and altered tail carriage, mainly after diagnostic injection.

Death or euthanasia directly related to sacroiliac injections was reported by 2.7% of clinicians after therapeutic injections and 0.9% after diagnostic injections. No clinicians witnessed an injection-related death more than once. Researchers found there was no correlation between the clinicians’ years of experience post-graduation, number of sacroiliac joint injections, or injection technique and complications experienced.

The study authors reported further studies must be completed to characterize complications in greater detail. They did not investigate the overall frequency of adverse events, but in a previous study the complication rate was extremely low. The researchers encourage horse owners and veterinarians to remember that adverse effects can occur with any injection, and clinicians don’t always know the specific causes of nerve dysfunction.

Sue Dyson, MB, PhD, DEO, FRCVS, co-author of the paper noted “early and accurate diagnosis and treatment of lumbo-sacroiliac joint region pain will enhance equine welfare and performance.” The authors believe strongly in the use of diagnostic injections for accurate diagnosis of lumbo-sacroiliac joint region pain. They recommended using regular treatments to control clinical signs and adopting appropriate management strategies to provide pain relief for affected horses, thus improving both equine welfare and performance.

This study appeared in the Equine Veterinary Journal in January 2023.