Patient and Surgical Variability in the Primary Stability of Cementless Acetabular Cups for Computational Pre-Clinical Testing

Author: Dermot O'Rourke

O'Rourke, Dermot, 2017 Patient and Surgical Variability in the Primary Stability of Cementless Acetabular Cups for Computational Pre-Clinical Testing, Flinders University, School of Computer Science, Engineering and Mathematics

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The challenge in developing new acetabular cups is assessing their likely performance in a diverse population prior to clinical trials. Finite Element (FE) modelling has been used to evaluate prostheses for over 40 years but the majority of studies do not fully consider the high levels of variation among patients and during surgery. The aim of the research presented in this thesis was twofold: 1) explore the influence of patient and surgical variability in the primary stability of a cementless acetabular cup using Finite Element (FE) models of the hemipelvis and 2) develop time efficient methods to examine this variability in order to incorporate it into pre-clinical testing.

To allow a large number of models to be simulated in this work, a software pipeline with automated processes was developed to generate FE models of the implanted hemipelvis, simulate cup insertion and gait cycle loading, and post-process primary stability output metrics. The influence of patient variability on primary stability was explored with a cohort of 103 patient-specific models. Comparisons between quartile groups of patient-related factors suggested gaps between the cup and bone were larger in subjects with small acetabular diameters and depth. Meanwhile, there was evidence of higher micromotion during gait in higher bodyweight and lower bone quality quartile groups. The variability in primary stability in the cohort could be reasonably approximated with subsets of subjects that were sampled based on the extremes of patient-related factors.

To reduce the time cost of quantifying FE model sensitivity, a surrogate modelling approach was developed and illustrated with a model of the intact hemipelvis. There was a significant time and computational saving associated with a Kriging surrogate model which accurately predicted all strain output metrics based on a training set of 30 simulations. To explore the influence of surgical variability and determine influential parameters on the primary stability, the surrogate modelling approach was used with a Latin Hypercube Design on two implanted hemipelvis models. Regression analyses indicated interference fit was the most dominant parameter in both subjects. Taken together, the elements in this thesis form the foundations for the development of a computational tool that accounts for patient and surgical variability to help provide more thorough evaluations of new cementless cups during the development phase.

Keywords: total hip arthroplasty, acetabular cup, primary stability, finite element analysis, pre-clinical testing

Subject: Computer Science thesis

Thesis type: Doctor of Philosophy
Completed: 2017
School: School of Computer Science, Engineering and Mathematics
Supervisor: Prof. Mark Taylor