True submalleolar accessory ossicles causing impingement of the ankle.

True ossicle in the distal portion of the malleolus is only sporadically observed, and related disease has been rarely reported. We present two cases of atypical ankle impingement resulting from an ankle sprain. Plain radiographs revealed true submalleolar ossicles. Conservative treatment failed, and arthroscopy was performed. Instability of the ossicle and surrounding fibrotic soft tissue was evident; a gap between the ossicle and the tip of the malleolus seen during plantar flexion of the ankle disappeared in dorsal flexion, resulting in compression of the surrounding soft tissue. Arthroscopic excision of the accessory ossicle relieved the symptoms and enabled both patients to return to full preinjury activities.