MR-guided Focused Ultrasound (MRgFUS) Ablation for the Treatment of Nonspinal Osteoid Osteoma A Prospective Multicenter Evaluation D. Geiger, MD, A. Napoli, MD, PhD, A. Conchiglia, MD, L.M. Gregori, MD, F. Arrigoni, MD, A. Bazzocchi, MD, M. Busacca, MD, O. Moreschini, Prof, M. Mastantuono, MD, U. Albisinni, Prof, C. Masciocchi, Prof, and C. Catalano, Prof Investigation performed at the Department of Radiological, Oncological and Pathological Sciences, Sapienza University of Rome, Rome, Italy, the Department of Radiology, Istituto Ortopedico Rizzoli, University of Bologna, Bologna, Italy, and the Department of Radiology, University of L’Aquila, S. Salvatore Hospital, Coppito, L’Aquila, Italy Background: Magnetic resonance-guided focused ultrasound (MRgFUS) is a novel imaging-guided surgical technique that allows the performance of noninvasive and radiation-free ablation. Presently, computed tomography (CT)-guided radiofrequency ablation, a minimally invasive percutaneous technique, is the standard for treating symptomatic osteoid osteomas. The purpose of this study was to evaluate the use of MRgFUS ablation for the treatment of nonspinal osteoid osteomas in terms of technical success, complications, and clinical success through one year of follow-up. Methods: In this prospective multicenter study, thirty consecutive patients with a nonspinal osteoid osteoma were enrolled between May 2010 and April 2012 at three different university centers; twenty-nine of the patients were treated with use of MRgFUS. Lesions had been previously diagnosed on the basis of imaging, including dynamic contrast-enhanced MR. The mean number of sonications and energy deposition were determined. Technical success was evaluated through an as- sessment of complications immediately after treatment. Clinical success was determined on the basis of pain reduction as measured with a visual analog scale (VAS), recurrence, and long-term complications through twelve months. Results: Technical success of MRgFUS was observed for all twenty-nine patients. The mean number of sonications (and standard deviation) was 7 ± 3, and the mean delivered acoustic energy was 1180 ± 736 J. At the twelve-month follow-up, complete clinical success was observed in twenty-six (90%) of the twenty-nine patients (95% confidence interval [CI] = 84 to 95; mean VAS, 0 ± 0 points). Partial success was observed in three (10%) of the twenty-nine patients (95% CI = 5 to 16; mean VAS score, 5 ± 0 points); two of these patients subsequently underwent CT-guided radiofrequency ablation, and one underwent open surgery. Pain score values showed a significant reduction (p < 0.001) between baseline (mean VAS score, 8 ± 1 points) and post treatment (mean VAS score, 1 ± 2 points). No complications were observed. Conclusions: MRgFUS may be an effective and safe alternative approach in the treatment of nonspinal osteoid osteoma. A complete clinical success rate of 90% was demonstrated without adverse events. MRgFUS is totally noninvasive and eliminates radiation exposure. Level of Evidence: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence. A n osteoid osteoma is a benign, painful musculoskeletal tumor that usually occurs in young males 1 . Berg- strand, in 1930, was the first to describe this entity 2 , and Jaffe later characterized it in a small case series 3 . A typical feature is a nidus on radiograph 4 , and clinically, pain is often worse at night. Pain is initially managed with the use of Disclosure: None of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of any aspect of this work. None of the authors, or their institution(s), have had any financial relationship, in the thirty-six months prior to submission of this work, with any entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. Also, no author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article. Peer Review: This article was reviewed by the Editor-in-Chief and one Deputy Editor, and it underwent blinded review by two or more outside experts. The Deputy Editor reviewed each revision of the article, and it underwent a final review by the Editor-in-Chief prior to publication. Final corrections and clarifications occurred during one or more exchanges between the author(s) and copyeditors. 743 COPYRIGHT Ó 2014 BY THE J OURNAL OF BONE AND J OINT SURGERY,I NCORPORATED J Bone Joint Surg Am. 2014;96:743-51 d http://dx.doi.org/10.2106/JBJS.M.00903