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

VARIATION OF MICRO-ARCHITECTURE AND APPARENT-LEVEL
MECHANICAL PROPERTIES AT DIFFERENT LOCATIONS
WITHIN THE FEMORAL HEAD
1. ABSTRACT
M. Crabbe 1 , B. Esteban 1 , R. Ramaesh 2 , P. Jenkins 3 , P. Pankaj 4
Computational modelling of bone requires careful assignment of mechanical properties
due to bone's high degree of multi-scale heterogeneity and anisotropy. This study
investigates the effect of bone micro-architecture on its mechanical properties, in
particular the variation of apparent stiffness within the femoral head. Twelve femoral
heads from osteoarthritic and osteoporotic donors were assessed using micro-finite
element (µ-FE) analyses on geometry obtained from micro-computed tomography (µ-
CT) scans. Bone porosity was found to be the strongest indicator of Young's modulus,
with a correlation coefficient of 0.92. Young's modulus was also found to vary with
location within the femoral head, the stiffest region being at the centre of the femoral
head. The principal stiffness directions within the femoral head vary significantly with
location. Additionally, OA bone was to found be 39.1% stiffer than OP bone on
average. These studies have implications in optimising arthroplastic implant placement.
2. INTRODUCTION
Osteoporosis (OP) and osteoarthritis (OA) are bone conditions that develop with age
and lead to a change in the mechanical properties of bone [1, 2]. This may result in an
increased risk of fracture, particularly of the hip [3]. Due to our aging global population,
the number of hip fractures is expected to increase significantly [4]. Bone implants such
as dynamic hip screws and proximal femoral nails can be used to treat hip fractures [5].
However, implant failure is not uncommon [6, 7], which suggests a need for a better
understanding of bone mechanical behaviour at the proximal femur.
Several studies attempt to model medical implants in the hip [8, 9, 10], but are
undermined by the use of generic input parameters that may not apply on a patientspecific
basis. Patient-specific modelling is emerging as a useful tool in diagnosis and
pre-clinical trials [11]. While determining geometry for patient-specific models is by
and large a resolved issue, determination and assignment of material properties remains
a difficult process [11].
1
Student, Alexander Graham Bell Building, School of Engineering, The University of Edinburgh, West
Mains Road, The King’s Buildings, Edinburgh EH9 3JL, UK.
2
Student, Chancellor's Building, Royal Infirmary of Edinburgh, Old Dalkeith Road, Edinburgh EH16
4SB, UK.
3
Orthopaedic Research Fellow and Clinical Lecturer, Chancellor's Building, Royal Infirmary of
Edinburgh, Old Dalkeith Road, Edinburgh EH16 4SB, UK.
4
Senior Lecturer, Alexander Graham Bell Building, School of Engineering, The University of Edinburgh,
West Mains Road, The King’s Buildings, Edinburgh EH9 3JL, UK.