LAUSR

The union rate of wire fixation after median sternotomy remains unsatisfactory. We developed a novel osteoconductive sheet composed of hydrophilized hydroxyapatite, and evaluated its osteogenetic effect when interposed between sternal halves in a canine model. Eighteen canines were divided equally into groups based on the hemostatic agent used: osteoconductive sheet (S), none (C), and bone wax (BW). After median sternotomy, the sternal halves were closed by wire fixation. In each group, three canines were euthanized at 1 month, while three were euthanized at 2 months. Resected sternums were mechanically assessed by the three-point bending test, radiographically assessed by micro-CT, and pathologically assessed to quantify the osteogenesis between sternal halves. Compared with the BW group, the S group had a greater maximum stress at 1 month (S: 322.9±107.7 N, C: 233.0±62.7 N, BW: 124.9±88.4 N; p=0.025), and greater maximum shear force at 1 months (S: 1.92±0.67 N/m2; C: 1.23±0.28 N/m2; BW: 0.68±0.41 N/m2; p=0.025). Micro-CT revealed that the S group had more osteogenesis than the BW group at 1 month (25.7±9.8% versus 6.9±9.2%), and 2 months (34.0±15.1% versus 14.8±9.4%); the respective values in the C group were 17.1±7.2% and 29.7±9.3%. Pathological examination revealed that the S group had the greatest osteogenetic area at 2 months (S: 38.8±18.8%; C: 24.5±6.9%; BW: 24.7±18.6%). Adjuvant osteoconductive therapy using a cotton-like hydroxyapatite sheet in addition to wire fixation significantly improved sternal healing compared with BW. This new material also showed relatively better outcome than the C group.