Fluid-filled swellings in the rear aspect of the tendon/fetlock area—called 'windpuffs,'” or synovial effusion of the tendon sheath—are a common condition in horses. | Photo: The Horse Staff

These fluid-filling swellings often are just blemishes, but attention should be given if they are new or associated with lameness.

Windpuffs are soft, fluid-filled swellings toward the back of the fetlock joint, resulting from inflamed deep digital flexor tendon sheaths. Most commonly, these puffy enlargements are symptomless blemishes–old and cold, the result of years of hard work. In some instances, however, the horse might be lame from recent injury to the tendon sheath, with marked heat and pain in the area, when you flex the joint or palpate the swelling.

Tim Lynch, DVM, Dipl. ACVS, who focuses on equine lameness cases at Peterson & Smith Equine Hospital in Ocala, Fla., says many horses have windpuffs, especially in the rear legs, with no associated lameness.

“The swellings occur where the digital flexor tendon sheath covers the two tendons that go around the back of the fetlock,” says Lynch. “This sheath has a synovial lining, just like a joint