OsteoSCREW - A morphology based failure criterion for implanted bone screws

• Project number: LSC17_004
• Project Management: Andreas Reisinger, Karl Landsteiner University for Health Sciences / Division of Biomechanics
• Project partners: AIT Austrian Institute of Technology / Center for Health & Bioresources
• Project duration: 48 months from 1 June 2019

Background

Complex bone fractures often need to be treated by trauma surgery. The individual bone fragments are fixed with implants (plates or rods) to stabilise the fracture. The implants are anchored with bone screws, among other things. Unfortunately, these screws can loosen or break out if the patient puts too much stress on the injured bone or if the bone quality - and thus the anchoring - is not sufficient. The implant must then be replaced in a new operation. This represents a considerable and above all additional burden for the patient, but also for the healthcare system. In this project, a computer-based screw failure criterion is to be developed, with the help of which one can predict whether a certain screw will withstand the stresses in a certain patient or not. To develop this failure criterion, a large number of bone specimens with implanted bone screws will be examined. These bone screw units are CT scanned and the screw head is loaded in different directions in a mechanical testing machine. The fracture loads of all samples are then related to the respective bone morphology (density, architecture) in the vicinity of the screw, which is obtained from the CT images. The result is a mathematical relationship that indicates the fracture load of this screw for a specific bone structure and loading direction. The screw material used is standard titanium and a new type of biodegradable magnesium that can dissolve in the human body. This would eliminate the need for the surgical procedure normally performed to remove the implant after bone healing. In order to bring this promising material closer to clinical use and to gain know-how, the magnesium screws are degraded in a controlled manner and their breaking loads are compared with those of normal titanium screws.