Mechanical Testing of Variable Angle Locking Screws for a New Proximal Humeral Plate

Author: Ryan Spry

Spry, Ryan, 2017 Mechanical Testing of Variable Angle Locking Screws for a New Proximal Humeral Plate , Flinders University, School of Computer Science, Engineering and Mathematics

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This project was performed in conjunction with a local company, Austofix, in the development of their new proximal humeral plate design. This project was designed to test the performance of the Variable Angle Screw Technology (VAST) that the company has designed to incorporate Variable Angle (VA) locking screws into their proximal humeral plate design.

In this project, relevant literature has been explored, from looking at potential risks of proximal humeral fractures and anatomy, to surgical techniques and proximal humeral plate design. This will provide an appropriate background and understanding on the intricacies of proximal humeral plate development. Throughout the literature review, discussions have been incorporated on how aspects of the fixation plates use can affect the design and development of the plate. The review also observes trends in the biomechanical testing of these plates.

The literature was used to observe the current style and types of proximal humeral plate testing, in relation to biomechanical testing and review studies. This provided great insight into the trends of these types of testing techniques as well as showing why different tests have been performed. It was key to observe the common methods of testing, as well as the differences between testing techniques.

This project has used the information gained by the literature and standards to help develop and test the new proximal humeral plate design. The testing that has been designed has incorporated information gained by the literature and standards, as well as being based on the requests given by Austofix and restrictions based on testing equipment. This has resulted in the design of three testing methods and the investigation into two other potential methods of testing.

The focus of testing for this project was to evaluate the performance of the VAST feature Austofix has designed, which allows the use of VA screws. The use of VA screws is a recent development in the field, providing flexibility during surgery. This is due to VA screws being able to be inserted over a range of angles.

This VA technology provides significant advantages over fixed angle screws and has shown to have a better performance. As this technology is still new, there needs to be significant testing to ensure that performance has not been compromised with the VA design. This has been performed during this project by observing the performance of a single VAST hole feature and VA screw interface. These constructs underwent a torque and ramp loading test, to observe the designs performance and the effect of differing tolerances and angles of insertion. This involved the screws being inserted into the button constructs in accordance with standard torque, to observe screw locking and head protrusion. Those specimens that passed the torque test were then ramp loaded at 5 mm/min, using a testing jig based on reviewed literature. This shear loading was used to observe the maximum force achieved before failure of the specimen occurred. Full results and discussion, are outlined in this report. The information obtained will help determine the direction of the project and also address any design changes. Additionally, a cyclic fatigue loading test was designed. This testing method has currently not been utilised, but may potential be performed by the end of the project.

Due to some constraints of the project not all testing was performed. In the report, we will discuss some of the limitations and how some of these limitations were overcome. For those testing methods that have not been finalised, a future works discussion has been performed outlining the importance of these testing methods.

Keywords: Proximal, Humerus, Plate, Variable, Locking, Screws

Subject: Engineering thesis

Thesis type: Masters
Completed: 2017
School: School of Computer Science, Engineering and Mathematics
Supervisor: John Costi