During arthroscopy on the left ankle of a 22 years old patient, there was an incidental finding. With inspection a thick fibrous layer was covering the cartilage of the talus. It could easily be separated from the underlying cartilage. We postulate that it resulted from an intra-articular bleeding leaving a layer of fibrin and fibrous tissue covering the cartilage.
P.S. This is the same patient as Picture of the Week Elite runner with anterolateral pain. We postulated that the septum is a result of the same pathology.