 Sternum Screw: Analysis of a Novel Approach to the Closure of the Chest After Surgery
(#2001-83468 ... September 9, 2001)
Rajwinder S. Jutley1,2, Duncan E. T. Shepherd1, David W. L. Hukins1, Robert R. Jeffrey2
1 Department of Bio-Medical Physics & Bio-Engineering, University of Aberdeen, Aberdeen, Scotland, UK
2 Cardiothoracic Surgery, Grampian University Hospitals NHS Trust, Aberdeen, Scotland, UK
ABSTRACT
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.
AUTHOR/ARTICLE INFORMATION
Acknowledgements
The authors wish to acknowledge the technical assistance provided by Mr. Edward Stevenson, Department of Bio-Medical Physics and Bio-Engineering, Aberdeen University, in manufacturing the sternum screws used in this study.
Submitted September 4, 2001; accepted September 9, 2001.
Address correspondence and reprint requests to: Dr. B.M. Fabri, FRCS Ed, Consultant Cardiac Surgeon, The Cardiothoracic Centre, Thomas Drive, Liverpool, L14 3PE, Phone: 44 151 2932397, Fax: 44 141 2208573, Email: bmfabri@ukonline.net
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