Chemical arthrodesis destroys the cartilage of the joint, producing ankylosis, and may also reduce pain immediately due to neurolysis. Often intra-articular injection of monoiodoacetate (MIA) or ethyl alcohol is used. Ethyl alcohol has several advantages over MIA, including decreased pain (MIA produces severe pain for several hours following injection), lower cost, and easy access. Chemical arthrodesis is commonly performed to treat osteoarthritis of the lower hock joints. These joints have little motion and can fuse without affecting the movement of the horse. Chemical arthrodesis has the potential to greatly improve chronic lameness which is not responding to IA anti-inflammatories, but carries the risk of severe complications, including joint sepsis, cellulitis, and severe lameness. Chemical arthrodesis is cheap, simple, and relatively noninvasive, but is potentially disastrous if the proximal intertarsal joint communicates with the high-motion tarsocrural joint. For this reason, a contrast study is often recommended prior to treatment to ensure no communication occurs between the two joints. Chemical arthrodesis has the potential to damage the joint cartilage without fusing the joint, leading to increased pain and lameness.Penraat, Jan H., et al. "An evaluation of chemical arthrodesis of the proximal interphalangeal joint in the horse by using monoiodoacetate." Canadian Journal of Veterinary Research 64.4 (2000): 212. Chemical arthrodesis is less successful when used in the pastern joint, and often surgical arthrodesis is preferred.Watts A. Making Sense of Pastern Arthrodesis Approaches. Proc. ACVS (2012).
