Osteoid Osteoma of the Trochlea Tali: A Rare Cause of Treatment-resistant Ankle Pain.

BACKGROUND: Osteoid osteoma is a benign but painful bone tumour that typically occurs in the long bones of young adults. Intra-articular localisation in the trochlea tali is rare and may significantly delay diagnosis. CASE REPORT: We report the case of a 41-year-old patient presenting with persistent, predominantly nocturnal pain of the right ankle joint, despite previous arthroscopic treatment of an osteochondral lesion. Initial conventional imaging was unremarkable. The diagnosis of an osteoid osteoma of the trochlea tali was established only after targeted re-evaluation using contrast-enhanced magnetic resonance imaging (MRI) and high-resolution computed tomography (CT). A diagnostic trial with acetylsalicylic acid resulted in marked symptom relief and further supported the suspected diagnosis, consistent with the known NSAID sensitivity of osteoid osteoma. Definitive treatment was performed using CT-guided radiofrequency ablation (RFA). The patient was completely symptom-free four weeks after the intervention. CONCLUSION: This case highlights the diagnostic challenges of intra-articular osteoid osteomas in atypical locations. Careful clinical assessment, appropriate imaging, and interdisciplinary collaboration are essential for timely diagnosis and successful treatment.