OBJECTIVES: Bone wax is frequently used to diminish bleeding after sternotomy. Water-soluble polymer wax has been shown to diminish postoperative bleeding and, unlike traditional bone wax, to be absorbed and removed by the organism in an unchanged state. We have previously shown that bone wax impairs early bone healing after sternotomy, whereas polymer wax does not. This difference was observed 6 weeks postoperatively and questions arose as to whether these effects were long term. Therefore, we hypothesized that bone wax impairs bone healing in sternotomized pigs 6 months postoperatively, whereas polymer wax does not.

METHODS: Fourteen Landrace/Yorkshire pigs were sternotomized and then randomly assigned to haemostasis by either bone wax (WAX-group) or water-soluble polymer wax (POL-group). After 6 months, the pigs were euthanized and the sternum was removed and prepared for further assessment. Bone fracture strength and bone stiffness were determined using a modified three-point bending test, whereas bone healing was examined by means of quantitative histology. Six pigs died before the end of the study due to failure to thrive, valve prosthesis endocarditis and coronary artery occlusion.

RESULTS: The mechanical testing showed no difference between groups with regard to fracture strength [WAX-group versus POL-group; 214.8 (85.5-478.5) vs 203.8 (90.4-478.5) N, P = 0.986] or maximum stiffness [213.0 (81.5-409.5) vs 348.5 (23.3-689.5) N/mm, P = 0.128]. Histology showed predominance of fibroblast-covered surfaces [10.6% (1.8-23.3%) vs 4.1% (0.0-13.0%), P < 0.001] and fibrous tissue volume [45.4% (6.9-82.0%) vs 17.4% (2.9-55.0%), P < 0.001] in animals treated with bone wax. The volume fraction of calcified bone tended to be higher in the POL-group [26.8% (4.3-35.8%) vs 16.7% (1.5-35.8%), P = 0.065]. Granulomas comprised 12.5% (0.0-78.9%) of the volume fraction in the WAX-group compared with 0.0% (0.0-0.0%) in the POL-group (P < 0.001).

CONCLUSION: Bone wax and water-soluble polymer wax had similar long-term effects on bone mechanical properties. Histology confirmed our hypothesis and showed a more extensive foreign body reaction in animals treated with bone wax than in those treated with water-soluble polymer wax.