Joint swelling results from excess fluid within the joint capsule, thickening of the structures surrounding the joint, or a combination of both. Swelling of multiple joints is relatively rare in horses.

It can result from conformation or wear-related causes. This is common in performance horses of any discipline that have had long careers of heavy or fast work. Many of these old campaigners have multiple fetlock joints and tendon sheaths that contain excess fluid and thickened joint lining. This is a response to repetitive trauma over a long period. It may or may not be accompanied by lameness.

In younger horses with no history of repetitive work-related trauma, we consider inflammatory conditions, infectious diseases and developmental diseases like osteochondrosis (OCD) as being possible causes for swelling of multiple joints.

In foals, multiple swollen joints with severe lameness and reluctance to move is typical of infected (septic) joints, a life-threatening problem. Swelling above joints in growing horses is associated with inflammation and swelling of the growth plates (physitis).