ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

DEVELOPMENT OF A NEW COMPUTATIONAL TOOL FOR RAPID
ANALYSIS OF IMPLANT POSITIONING EFFECTS IN TOTAL HIP
REPLACEMENTS
M.T. Bah 1 , V.B. Xuan 2 , S. Richards 2 , M. Nicolas 2 , G. Champion 2 , M. Browne 1 ,
R.Bryan 2 and P.G. Young 2
1. ABSTRACT
The advent of image-based Finite Element (FE) modeling, advanced softwares and the
amount of computer power are increasingly easing the pre-clinical assessment of
implant performance in Total Hip Replacements (THRs). Computer Tomography (CT)
data can be processed faster and high-quality meshes that can accurately represent the
implanted femur geometries can now be generated. Accounting for variability in
implant positioning, however, requires many scenarios including different combinations
of alignment to be simulated and analysed. This paper shortcuts this iterative, tedious
and time-consuming process by customising and applying newly developed mesh
refinement and scripting tools, convenient for multiple simulations and statistical
analyses. An efficient Design of Computer Experiments (DOE) is conducted; the
considered femur is implanted with an implant in pre-defined positions that best sample
and adequately replicate the possible combinations of ante/retroversion, varus/valgus,
anterior/posterior orientations and implant offsets. The resulting micromotions are then
post-processed to arrive at implant positions that correspond to the best THR
performance. For a specific patient, the proposed tool can help both orthopaedic
surgeons and engineers when comparing different prostheses or searching for optimal
positioning.
2. INTRODUCTION
When a cementless THR is performed, the femur is either reamed or broached prior to
press-fitting of the metal stem into the bone in a pre-defined position. Unfortunately,
optimal implant positioning depends on the surgical approach, the design of the
prosthesis and the subject’s anatomy even when CT-based pre-operative planning
softwares and computer navigation are used. Ideally, surgeons want to cut the femur in a
neutral position thereby reducing for example the difference between the anatomical
and surgical reconstructed femoral anteversion [1]. An anteverted femoral stem can
increase the risk of dislocation. FE-based modeling can help in accounting for the
effects of variability in implant positioning. Typically, a CAD software is used to replace
the implant; re-perform Boolean operations (cutting femur head, reaming, joining
implant and femur, partitioning, etc...) and export the new mesh to an appropriate FE
solver for solution. This process can require various computer softwares from
1 Bioengineering Science Research Group, Faculty of Engineering and the Environment, University of
Southampton, Southampton SO17 1BJ, England, UK
2 Simpleware Ltd, Bradninch Hall, Castle Street, Exeter EX4 3PL, England, UK