Sternum screw: analysis of a novel approach to closure of the chest after surgery

BACKGROUND: To show the benefits of using a novel approach to closure of the median sternotomy through a mechanical model and mechanical testing. Simple cannulated screws are placed on either side of the sternotomy. Conventional stainless steel wire is passed through the cannula of each screw and the sternotomy is closed in the usual manner. METHODS: Hertzian contact analysis was used to estimate the stress between the wire and the sternum. Mechanical testing was used to compare using wire on its own with a sternum screw plus wire. Ten samples of balsa wood (sternum substitute) had wire placed through a hole in them, while a further ten samples were fitted with a cannulated screw and had wire passed through the screw cannula. The wire was connected to a materials testing machine, which applied tension to the wire until the wire or screw cut through the wood. RESULTS: The analysis showed that the mean stress between the wire and the sternum decreases with increasing wire diameter. At low diameters of wire the stress in the sternum can be comparable to the failure stress of bone. Using a cannulated screw reduces the stresses in the sternum. The mechanical testing showed that the wire cut through the wood at a mean load of 104 N, whereas the sternum screw cut through the wood at a mean load of 209 N (p = 0.007, Mann-Whitney Test). CONCLUSIONS: Closing a median sternotomy with cannulated screws plus wire should reduce the occurrence of sternal dehiscence.