Intraoperative cooling of iliac bone graft: An experimental evaluation of cell viability

Purpose: A cancellous iliac bone graft is used to treat alveolar clefts. A few hours can exist between graft harvest and placement into the alveolar defect. The purpose of this study was to determine whether intraoperative cooling of bone optimizes viability and to evaluate cellular preservation of cooled graft over time. Patients and Methods: Twelve cancellous iliac bone graft specimens were obtained prospectively from consecutive patients undergoing alveolar cleft repair. Each sample was collected during graft procurement and divided into 3 groups: group 1 (immediate analysis), group 2 (analysis after 2 hours at room temperature), and group 3 (analysis after 2 hours on ice). To generate a viability curve, iliac bone specimens were stored on ice and assayed immediately and hourly for 8 hours. Resazurin, an oxidation-reduction indicator of metabolically active cells, was used to assess cellular viability (normalized relative fluorescence units). Results: Group 1 (n = 7,370) had more active cells than did group 2 (n = 4,104) or group 3 (n = 5,005; P =.03). Group 3 had greater viability than group 2 (P =.03). Cellular preservation of the cooled graft was 100% at the immediate analysis, 98.4% ± 13.9% at 1 hour, 91.8% ± 9.8% at 2 hours, 83.1% ± 31.8% at 3 hours, 71.8% ± 27.2% at 4 hours, 71.4% ± 16.9% at 5 hours, 69.9% ± 19.0% at 6 hours, 70.0% ± 22.5% at 7 hours, and 66.7% ± 13.3% at 8 hours. Conclusions: Storing iliac bone graft on ice rather than at room temperature optimizes cellular viability, with cooled bone demonstrating 22.0% more active cells after 2 hours. Cellular loss of cooled graft plateaued after 4 hours. Clinically, the iliac graft should be maintained on ice until placed into the alveolar cleft.