Magnetic resonance imaging is appropriate for determining the osteotomy plane for appendicular osteosarcoma after neoadjuvant chemotherapy.

There are no standard criteria for determining a sufficient resection margin in the treatment of osteosarcoma. The purposes of this study are to evaluate clinical outcomes using T1-weighted magnetic resonance imaging (MRI) for determining the margin of resection and to compare that with the results of different imaging modalities. Seventeen patients diagnosed with osteosarcoma who underwent en bloc resection with a margin of 2-3 cm based on T1-weighted MRI following chemotherapy were studied. Imaging modalities including conventional radiography, MRI, computed tomography (CT), visual assessment, and histopathological examination were performed and compared. Survival rates were determined. After follow-up of 45.5 ± 13.8 months, no local tumor recurrence was observed in any patient. The 1-, 3-, and 5-year survival rates were 94.1, 82.3, and 76.5%, respectively. The differences in the measurement errors among the five methods were analyzed using pathology as the gold standard. Errors were smallest using T1-weighted and fat-suppressed MRI. There were no significant differences between the measurement results of postoperative histopathological examination and that of T1-weighted imaging or T2 fat-suppressed imaging. The measurement results of radiography and CT were significantly different from that of postoperative pathological findings (P < 0.05). Thus, MRI examination is superior to radiography and CT for determining tumor invasion in patients with osteosarcoma. A resection margin of 2-3 cm determined by MRI provides adequate treatment, while minimizing tissue removal.