Improved Healing by Adjuvant Osteoconductive Therapy Using a Novel Cotton-Like Hydroxyapatite Sheet After Median Sternotomy.

ABSTRACT

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, 3 canines were euthanized at 1 month, while 3 were euthanized at 2 months. Resected sternums were mechanically assessed by the 3-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 month (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% vs 6.9% ± 9.2%), and 2 months (34.0% ± 15.1% vs 14.8% ± 9.4%); the respective values in the C group were 17.1% ± 7.2% and 29.7% ± 9.3%. Pathologic 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.