Osteoid osteoma of the talus adjacent to the subtalar joint: a rare location and diagnostic challenge.

Introduction and importance: Osteoid osteoma is a common benign bone tumor, but lesions located in the talus, especially those adjacent to the subtalar joint, are relatively rare and prone to misdiagnosis. Its clinical and imaging manifestations are often atypical, which can lead to delayed diagnosis and inappropriate conservative treatment. Accurate imaging evaluation and appropriate surgical management are critical for symptom relief and functional recovery. Case presentation: We present a 20-year-old male with chronic left ankle pain that worsened at night and with weight-bearing. Initial MRI suggested bone marrow edema and ligament injury, leading to a misdiagnosis of ankle synovitis and sprain. Subsequent CT clearly identified a 5-mm nidus at the medial inferior margin of the left talus. The patient underwent open resection with intraoperative CT-guided K-wire localization. Postoperative histopathological examination confirmed osteoid osteoma. At the 1-year follow-up, the patient was pain-free and had fully resumed daily activities. Clinical discussion: Talar osteoid osteoma is prone to misdiagnosis because its symptoms resemble those of ankle sprain, synovitis, or impingement. CT is the gold standard for detecting the nidus, while MRI frequently shows nonspecific bone marrow edema. Surgical excision remains a reliable treatment method. CT-guided K-wire localization improves accuracy, minimizes bone damage, and ensures complete resection, avoiding incomplete ablation and the recurrence risk associated with percutaneous radiofrequency ablation. Conclusion: Osteoid osteoma of the talus is a rare but significant cause of chronic ankle pain and is easily misdiagnosed. CT is essential for early and accurate diagnosis. For juxta-articular lesions, CT-guided K-wire localization followed by open resection is safe and effective, completely relieving symptoms and achieving good long-term outcomes.