In cases of complete fixation, the stifle and hock become locked in extension. | Photo: Courtesy Dr. Maggie Peitzmeier

Veterinarians most commonly see this condition in young horses and ponies. It occurs when the medial patellar ligament (which connects the patella, in the stifle joint, to the tibia below) gets ‘stuck’ on the femur during limb extension. The signs can be quite variable in severity and frequency.

In cases of complete fixation, the stifle and hock become locked in extension, and the horse might hop and drag his toe behind him to move. When the ligament releases, it appears as a jerking movement that some owners confuse with stringhalt (a neurologic disease that causes uncontrollable, exaggerated hind-limb movement).

With the severe form the leg can be stuck behind the horse momentarily, for a few minutes, or even permanently. In more mild, intermittent cases the release of the ligament is delayed and the horse has a jerky gait during limb flexion. Walking down a hill, backing, and walking in tight circles make these signs more noticeable