Heterotopic ossification development within the interosseous membrane of the ankle is an uncommon occurrence after routine ankle sprains. We present a case of a high school football player who sustained a syndesmosis ankle sprain. After 4 weeks, he continued to have pain, swelling, and range of motion restriction despite being treated with cryotherapy, NSAIDs, supportive taping, and progressive rehabilitation. The radiographs revealed a heterotopic ossification within the interosseous membrane of the distal extremity. The patient was initially treated conservatively and went on to have surgical excision with an excellent result. Symptomatic patients will require definitive surgery even without frank synostosis.