Intraarticular Entrapment of Os Subfibulare Following a Severe Inversion Injury of the Ankle: A Case Report

INTRODUCTION: Anterior Talofibular Ligament (ATFL) rupture is the most commonly injured anatomic structure in lateral ankle sprain. In some cases, ATFL avulsion fracture from the lateral malleolus may occur instead of purely ligamentous injuries. The ATFL avulsion fracture is detected as a small ossicle at the tip of lateral malleolus on direct radiographs, which is called os subfibulare in chronic cases. CASE PRESENTATION: Severe displacement of this ossicle to the tibiotalar joint space is an extremely rare injury. Herein, a case of intra-articular entrapment of os subfibulare following a severe inversion injury of the ankle, which caused a diagnostic challenge was presented. CONCLUSIONS: To the best of our knowledge, this is the first case of entrapment of os subfibulare in the talotibial joint space. Fixation of the os subfibulare to lateral malleolus resulted in union and excellent functional results.