Patellar Osteoid Osteoma as a Cause of Intractable Anterior Knee Pain - A Case Report and Systematic Review of Literature.

Introduction Patellar involvement by osteoid osteoma is very rare. Osteoid osteomas that present as anterior knee pain are frequently misdiagnosed which leads to initial delay in treatment. Plain radiology has poor diagnostic yield. A combination of high index of suspicion, appropriate imaging, and complete ablation of the lesion is necessary to achieve good outcomes. Case Report A 16-year-old male presented with insidious onset anterior knee pain for the past 2 years. The pain was intermittent and mild; however, it increased progressively in intensity and frequency, which was worse at night. Examination reveals minimal effusion in the suprapatellar pouch, full range of motion of the knee, and wasting of the quadriceps. Serum biochemistry parameters were in normal limits. Plain radiographs did not reveal any significant abnormality. On magnetic resonance imaging, a hypointense, punctate lesion surrounded by a small hyperintense zone was noted at medial aspect of patella. A computed tomography scan showed the lesion with a central nidus, surrounded by a sclerotic rim, confirming the diagnosis of osteoid osteoma. Radiofrequency ablation was carried out without any post-procedural complications. The patient was pain free a few days after the procedure. At 14-month follow-up, there was no recurrence of symptoms. Conclusion Osteoid osteomas that present as anterior knee pain are frequently misdiagnosed. Plain radiology has poor diagnostic yield. A combination of high index of suspicion, appropriate imaging, and complete ablation of the lesion is necessary to achieve good outcomes.