Interleukin-1β as an articular process joint intra-articular model induces synovitis and signs of acute neck pain in horses.

Objective: To develop and define a model of acute neck pain in an equine cervical articular process joint (APJ) using recombinant equine IL-1β (reIL-1β).

Methods: 12 horses in this experimental study received a randomly assigned, unilateral intra-articular injection of 50 ng (n = 6) or 100 ng (n = 6) of reIL-1β and saline (contralateral side as control) into the C5-to-C6 APJ. Blinded ultrasonographic, clinical, and biomechanical parameters were evaluated between 4 hours and 14 days.

Results: There was a significant increase in APJ effusion on ultrasonographic examination that peaked at 24 hours (P = .0256; effect size, 0.8312; CI, 1.0594 to 0.629). There was a time effect on the clinical examination score (myofascial pain and stiffness) and a significant decrease in stride length and velocity at 24 hours. There was an adverse event (extravasation of injectate) in 1 horse.

Conclusions: Ultrasonographic evidence of the presence and severity of APJ effusion was readily identified and tracked over time. Unilateral injection of the APJ with reIL-1β induced clinical signs of myofascial pain, neck stiffness, and gait adaptations. Using individual control horses, rather than a contralateral saline injection within the same horse, would improve our understanding of the clinical presentation of acute APJ pain using this model.

Clinical relevance: Diagnosing the presence, localization, and clinical effects of neck pain in horses remains challenging and would benefit from the establishment of an experimental model. The induction of acute synovitis using reIL-1β within the C5-to-C6 APJ opens the door for future studies to ultimately better understand equine cervical pain and dysfunction.