Osteoid Osteoma of Talus - A Rare Occurrence Mimicking Ankle Arthritis: A Case Report.

Introduction: Osteoid osteoma is a benign, bone forming tumor which accounts for nearly 10% of all benign bone tumors. The foot is very rarely involved, with only around 2% of osteoid osteomas being reported to occur in bones of the foot. Osteoid osteoma of the talus could present as symptoms mimicking monoarticular arthritis of the ankle. We present a case of osteoid osteoma occurring in the neck of talus, presenting such a diagnostic dilemma. Case Report: A 13-year-old male child had complaints of pain and swelling in his right ankle since 1 year. The pain was predominantly aggravated at night and partially relieved by non-steroidal anti-inflammatory drugs. On examination, we found a diffuse, ill-defined, and soft swelling over the anteromedial aspect of the right ankle, which was anterior and inferior to the medial malleolus. The movements at the ankle joint were restricted and painful. Lateral radiograph of ankle revealed a solitary, osteolytic, and circular lesion involving the neck of the talus. Computed tomography (CT) scan showed a well-defined, lucent, and intramedullary lesion with a sclerotic rim in the neck of talus. The child was diagnosed to have osteoid osteoma of the neck of talus. We performed percutaneous CT-guided radiofrequency ablation (RFA) of the lesion. The child had complete relief of pain after the procedure. The child was followed up for 3 years and had no complaints of pain. Conclusion: Osteoid osteoma very rarely occurs in the talus. It can present as monoarticular arthritis involving the ankle joint and requires a high degree of suspicion to be identified. A CT scan remains the most accurate investigation to confirm the diagnosis. We found percutaneous CT-guided RFA to have yielded good outcome without recurrence.