A swelling on the limb that might or might not be accompanied by lameness could be the first sign of bursitis or synovitis. These are similar, moderately common inflammatory conditions of the structures that produce synovial (joint) fluid.

“When synovial structures become inflamed, distension (swelling) and pain can follow,” says Joanne Kramer, DVM, Dipl. ACVS, clinical assistant professor of equine surgery at the University of Missouri. “Even worse, by-products of severe inflammation can damage cartilage in joints, tendons in tendon sheaths, or set up adhesions (restrictive bands of scar tissue). Infectious bursitis/synovitis often causes severe lameness.”

Anatomy 101

Bursitis is inflammation of the bursa. “The bursa is a sac between the tendon and an adjacent bone that the tendon glides over,” Kramer says. “The sac is lined with a membrane that produces synovial fluid