Symptomatic Accessory Ossicle Near the Medial Malleolus Simulating Fracture Non-union: A Case Report and Literature Review.

Abstract

Introduction: Accessory ossicles of the ankle and foot are normal anatomical variants that are usually asymptomatic. The os subtibiale is a rare accessory ossicle located just inferior to the medial malleolus, with a reported prevalence of 0.9-1.2% in the general population. When symptomatic, it can mimic fractures or fracture non-union, leading to diagnostic confusion. Accurate diagnosis relies on careful clinical evaluation and appropriate imaging.

Case report: A 20-year-old male presented with persistent pain around the right ankle, 7 months after sustaining a twisting injury while walking. He was initially treated by a local bonesetter and presented late to our facility with unresolved symptoms. Clinical and radiological evaluation initially suggested a medial malleolus fracture non-union. However, further imaging revealed a well-corticated, smooth-margined bone fragment inferior to the medial malleolus, consistent with a symptomatic os subtibiale. The patient underwent open excision of the ossicle under spinal anesthesia. Intraoperative findings confirmed the diagnosis. Postoperatively, ankle range of motion and weight-bearing were initiated as tolerated. At the 1-year follow-up, the patient was pain-free and had regained full ankle function.

Conclusion: This case highlights the importance of differentiating between a medial malleolus fracture non-union and a symptomatic os subtibiale, particularly in patients presenting late after ankle trauma. Awareness of this rare entity and its imaging characteristics is crucial to avoid misdiagnosis and ensure appropriate management, leading to excellent clinical outcomes.