A computer-assisted guidance technique for the localization and excision of osteoid osteoma.

Osteoid osteoma is a small, benign bone neoplasm that consists of a well-demarcated nidus surrounded by a reactive zone of sclerosis.1,2 It is of unknown etiology and accounts for approximately 10% of symptomatic benign bone tumors.3 Initial treatment of patients with osteoid osteoma consists of nonsteroidal anti-inflammatory drugs (NSAIDs).4 If the pain is unresponsive to medical therapy or if patients cannot tolerate prolonged NSAIDs, surgical treatment is indicated. Classically, complete surgical excision has been the operative treatment of choice. However, lesions located in anatomic areas that are technically difficult to access, such as the femoral head or neck, carry considerable surgical morbidity. En bloc surgical resection has resulted in extended hospital stays, perioperative fractures, the need for bone grafts, internal fixation, or both, and delayed functional recovery.5 Localization of osteoid osteoma has been aided in the past by nuclear scanning, fluorescence with tetracycline, linear tomography, and intraoperative fluoroscopy. In the past decade, computed tomography (CT) guided radiofrequency ablation, alcohol ablation, and laser photocoagulation have been used extensively.6-8 This article presents a technique for the localization and excision of osteoid osteoma. Computer-assisted guidance allows intraoperative location of the nidus via optically tracked instruments. The nidus, once located, is precisely and accurately excised. CASE REPORT A previously healthy 19-year-old woman presented with dull pain in the right lower leg. No history of trauma was reported. The pain was most noticeable at night and NSAIDs provided temporary relief. Plain radiographs revealed a fusiform sclerotic lesion in the posteromedial aspect of the tibia (Figure 1). Computed tomography (General Electric, Milwaukee, Wis) confirmed an intracortical lucent area with associated reactive bone formation. Osteoid osteoma was suspected and operative treatment was chosen. Computer-assisted localization involves preoperative image processing and intraoperative guidance. Diagnostic CT was acquired on a conventional scanner using a protocol that was determined to provide excellent diagnostic images and images suitable for computer reconstruction. Computed tomography was processed with a custom software program