Localized pigmented villonodular synovitis as a rare cause of chronic anterolateral ankle pain in an equestrienne.

An unusual case of localized pigmented villonodular synovitis of the ankle as a rare cause of chronic anterolateral ankle pain in a 16-year-old horsewoman is presented. Intra-articular nodular forms of pigmented villonodular synovitis can only be diagnosed arthroscopically, macroscopic and microscopic aspects being typical. We believe that this lesion is more likely a reactive process secondary to repetitive microtrauma rather than a true neoplasm. Our patient presented with pathology in the left ankle, the side by which one mounts and dismounts a horse, forcing, in both activities, ankle dorsiflexion. Moreover, an English saddle was used by our patient, upon which one rides with the ankle maintained in dorsiflexion. At arthroscopy, the soft-tissue mass was seen to be entrapped in the joint between the talus and the tibia at dorsiflexion of the ankle. This had caused a slowly progressive enlargement of the lesion because of fibrosis resulting from reactive inflammation associated with this repetitive microtrauma, thus causing irritation, pain, and synovitis due to impingement.