Relationship between bone union and degree of bone marrow fibrosis at resection margins of advanced mandibular ORN

Background The pathological evaluation of cancellous bone at resection margins of mandibular osteoradionecrosis (ORN) has not been well elucidated. Here, we developed a unique classification system for evaluating the degree of bone marrow fibrosis, one of most common pathological features, in patients with mandibular ORN, based on which we investigated its relationship with treatment outcome. Methods This study included 15 patients who underwent mandibulectomy and free fibula osteocutaneous flap reconstruction. The extent of mandibulectomy was determined, with safety margins of approximately 10 mm from the apparent osteolytic areas on preoperative computed tomography image. Special staining was performed on thin sections from center of the osteolytic areas (medial area) and bilateral resection margins, and the degree of bone marrow fibrosis was evaluated and investigated its relationship with presence of bone union as a treatment outcome. Results The degree of bone marrow fibrosis of medial area was significantly higher than those of resection margins. Although most resection margins had collagen fibers which indicate severe fibrosis, all transferred fibula flaps achieved bone union. Conclusion When mandibulectomy is performed with safety margins of approximately 10 mm from the apparent osteolytic areas, all transferred fibula flaps achieved bone union regardless of the degree of bone marrow fibrosis at resection margin. In other words, the association between severe bone marrow fibrosis at resection margins and treatment outcome was not seen. Clinical Relevance Setting safety margins of approximately 10 mm may achieve bone union, but further study is needed.