Severe Synovitis in Two Horses due to the Use of Irrigating Solutions Containing Methanol and Formaldehyde

Two horses were examined because of chronic lameness, which followed arthroscopy in one case, and tendon sheath lavage in a second case. Clinical investigations linked both cases to the use of irrigating fluids containing preservatives. The clinical signs were reproduced in a Shetland pony by injection and lavage of the carpal joints with the same fluid. Lameness was slow in onset and accompanied by profound periarticular fibrosis. Postmortem examination confirmed the presence of a severe, erosive, noninfectious arthritis that may have an immune-mediated component. Clinicians should read product labels carefully and be aware of the dangers of exposing synovial tissues to solutions containing preservatives.