Histological findings of regeneration in retrieved pasteurized bone grafts

Background: Despite a number of radiologic evaluations of the incorporation of pasteurized bone (PB) in human and histologic evaluations in animal models, there has been a scarce documentation regarding the histologic evaluation of PB from human. Herein, we present histologic findings of regeneration in retrieved PB graft from pediatric and adult patients. Methods: PB was retrieved for various reasons in 7 patients (10–52 years old). Two bone pathologists independently counted the number of empty lacunae and lacunae with living cells in up to 10 randomly selected fields on medium-power (H&E, ×200) for each patient. Regeneration of PB was assessed as the ratio of the number of lacunae with nucleated cells to that of whole lacunae, which was defined as the “repair rate (RR)”. Results: The mean interval between initial reconstruction and retrieval (graft removal time; GRT) was 47.4 months (range, 11–144 months). The length of original PBs ranged from 5.8 to 20.6 cm. Microscopic examination of PBs showed areas with empty lacunae indicating necrosis and other areas contained lacunae with nucleated osteocytes, indicative of regeneration. Some Haversian canals of the PBs were filled with fibrovascular tissue and surrounded by lamellar bones including living osteocytes. RR varied widely from 21.7 to 62.4% with a mean of 36.8%. It was much higher in adult patients (46.6–62.4%, mean = 55.3%) than in pediatric patients (21.7–28.6%, mean = 25.3%), which was correlated with GRT (pediatric patients; mean of 14 months, adult patients; mean of 72.3 months). In adult patients, RR was higher in a patient with prosthesis composite in the proximal humerus (Case No. 3; 62.4%). Conclusions: RR was higher in whom GRT was longer, being correlated with GRT in retrieved PBs. In terms of our histological observation, PB is thought to be an acceptable temporary biologic spacer in limb-sparing surgery for malignant bone or soft tissue tumors.