Symptomatic Os Subtibiale Following Injury: A Case Report of Failed Conservative Treatment, Leading to Differential Diagnosis Made Intraoperatively

INTRODUCTION: Os subtibiale is a rare accessory bone found adjacent to the distal tibia and is mostly asymptomatic. Differentiating it from a medial malleolar fracture is challenging. Most cases of acute ankle trauma that presents with an Os subtibiale are initially diagnosed as fractures by treating physicians at emergency centers. It is therefore critical for an orthopedic surgeon who gets referral for such cases to consider complete history of such patients to understand the cause of their symptoms. The goal is to avoid unnecessary surgical treatment and to realize that a symptomatic Os subtibiale can be successfully managed by conservative means. Nonetheless, certain cases may require surgical treatment if conservative treatment options fail. This is a case report of a patient that was diagnosed as a case of symptomatic Os subtibiale intraoperatively, after conservative options were unsuccessful. CASE PRESENTATION: An 18-year-old patient with an injured right ankle was referred to our clinic after failed attempts to resolve his symptoms conservatively. Based on our initial clinical and radiographic examination, the patient was continued on a conservative treatment plan assuming, it was a case of unsuccessful fracture union. After almost a year of failed conservative treatments, surgery was offered to the patient, with the understanding that the bone fragment might either be fused or completely removed based on intraoperative diagnosis. At surgery, it was observed that the bone fragment had the characteristic of an Os subtibiale. It presented as a round, smooth structure with well-formed cortical boundaries, and minimal attachment to the distal tibia. A diagnosis of symptomatic Os subtibiale was made intraoperatively, which was then successfully excised using standard orthopedic instrumentation. The patient healed uneventfully and reported a pain free, normal ankle range of motion at latest follow-up of 18 months. CONCLUSION: Accurate diagnosis of Os subtibiale continues to present a learning challenge for most orthopedic physicians as these cases are extremely rare and often asymptomatic. Our patient failed to respond to conservative treatment, which led to surgery and intraoperative diagnosis of Os subtibiale that was the pain causing agent.