Presentation
Painful ankle.
Patient Data
Os trigonum with marrow edema across and within the synchondrosis. Mild posterolateral ankle joint capsule thickening and edema. Small effusion of the subtalar joint. Small tendon sheath effusion of flexor hallucis longus adjacent to the os trigonum.
Loculated ganglion cysts arising laterally from the posterior subtalar joint adjacent to the lateral talar shelf / lateral calcaneum and peroneal tendons.
Upward bowing of the dorsal talonavicular ligament secondary to a talonavicular joint effusion, extends laterally into the sinus tarsi. Further effusion from the posterior subtalar joint extends anteriorly into the sinus tarsi.
Incidental unicameral bone cyst within the plantar aspect of the mid calcaneal body.
Case Discussion
Os trigonum syndrome is generally considered synonymous with posterior ankle impingement syndrome, although the latter can occur without the presence of an os trigonum, many of the other features of soft tissue inflammation are the same. Os trigonum are a common finding, and are usually asymptomatic - in this case, however, there is edema affecting the os trigonum and its synchondrosis with the talus in the appropriate clinical context.