Feasibility of polymer coated femoral stems and pre-cooling for improved triboperformance and stress distribution

Walsh, Justin (2020) Feasibility of polymer coated femoral stems and pre-cooling for improved triboperformance and stress distribution. [USQ Project]

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Abstract

A review of Australian Orthopaedic data showed that aseptic loosening was the leading cause of prosthetic failure over the past five years, marginally exceeding loosening of the acetabulum. This study looks at identifying and evaluating the feasibility of proposed improved approaches to the femoral stem and the insertion process. The primary theory being tested is that the use of polymer coatings on femoral stems in conjunction with pre-cooling can yield improved results in triboperformance and force distributions due to lower coefficients of friction, lower compressive strengths and lower shock transfer loading than traditional implant materials. The novel addition of temperature control will allow for the femoral stem to be physically smaller during the insertion process, then being allowed to expand to the full size once inserted in the body will reduce the mechanical damage and risk of fracture during insertion. The theoretical study is designed as a precursor before detailed designing, prototyping and live testing of polymer coated, pre-cooled femoral stems.

The study consisted of two key components, a material selection and a Finite Element Analysis (FEA). The key decision criteria of the material selection were to achieve mechanical properties closest to that of bone using the physical properties methodology. The highest performing material under this criterion was PEEK, followed closely by all other polymers already assessed as biocompatible by industry. The validation through simulation results showed that LDPE outperformed PEEK when it came to this testing.

The FEA was conducted to validate and quantify the benefits of the material selection and pre-cooling. Polymer materials showed a more even distribution of displacement, stress and strain. The polymers showed approximately 0.08mm of deformation, whereas the titanium has deformation values of 0 to 0.01mm. The distribution of stress was also far closer in the polymers when compared to titanium and zirconia. The addition of pre-cooling showed a reduction of deformation of up to 5% (0.0125 mm) at 5 o c for polymers but was negligible for Titanium stems. For the amount of effort required to pre-cool to fridge temperatures, this shows an extremely simple but promising change in the surgical procedure when polymers were used.

Polymer coatings on a titanium stem were found to be structurally stable with a factor of safety of at least 2 when supporting a force up to 10x of a 100kg person (10kN load). The results of this dissertation are extremely positive and stand as a sound grounding to further investigation including manufacturing and prototyping of real models which will allow for live testing. Continued research into this approach could lead to reduced revision rates as a result of aseptic loosening of the femoral stem.


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Item Type: USQ Project
Item Status: Live Archive
Additional Information: Bachelor of Engineering Honours (Mechanical)
Faculty/School / Institute/Centre: Current - Faculty of Health, Engineering and Sciences - School of Mechanical and Electrical Engineering (1 Jul 2013 -)
Faculty/School / Institute/Centre: Current - Faculty of Health, Engineering and Sciences - School of Mechanical and Electrical Engineering (1 Jul 2013 -)
Supervisors: Goh, Steven
Date Deposited: 09 Aug 2021 02:20
Last Modified: 10 Aug 2021 05:42
Uncontrolled Keywords: aseptic loosening, rosthetic failure, femoral stem, insertion process, polymer coatings, pre-cooling, triboperformance, force distributions
URI: http://eprints.usq.edu.au/id/eprint/43021

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