Osteoarthritis and IRAP

How long will a horse with osteoarthritis remain sound after successful IRAP treatment?

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Q. My horse was diagnosed with bilateral osteoarthritis of the pastern joints in the front legs, but we were never able to determine the exact location and cause. She is a large, heavybuilt 17.1-hand South African Warmblood. She trotted out sound in a straight line but was dead lame on a circle. We had nerve blocks and X rays done to determine the problem with no success, and we injected cortisone into the joint with no effect on her lameness. We then decided to try IRAP (interleukin-1 receptor antagonist protein), and it made her completely sound.

It has been three years now since the IRAP treatment. We now compete at dressage at elementary level and jump occasionally just to prevent my horse from becoming bored with flatwork. My question is how long will she continue to remain sound from the IRAP treatment? Should I repeat the IRAP treatment after a few years to ensure she remains sound, or should I wait until she presents with lameness? —Leigh-Ann Herselman, Menlo Park, South Africa

A. This is a great question because we don’t have any research at the moment that tells us about IRAP timing (i.e., in the long-term, what the best interval is for repeated IRAP treatment of joints). It sounds like your mare had a fantastic response to the treatment, and I am surprised at the duration of three years of soundness—this case is somewhat unusual. It may be that she had a minor transient injury to that joint, which responded very well to the IRAP and did not progress into a situation of chronic arthritis. This situation would be the most ideal type of case to treat, being able to intervene with treatment before arthritis becomes the main problem.

More often we are treating joints that are truly arthritic. The injury that caused the arthritis may be years in the past, and we are trying to manage the subsequent chronic inflammation and loss of structure in the joint. In these cases (especially when the horse is used athletically), I would expect to remedicate that joint with IRAP on an as-needed basis, as determined by the degree of arthritis and the intensity of the horse’s job. In other words, that might be a course of four weekly injections twice a year or annually

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Written by:

Jamie Textor, DVM, Dipl. ACVS, is an equine surgeon pursuing her PhD at the University of California, Davis, School of Veterinary Medicine.

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