Finite element modeling of hip resurfacing cup deformation

Abstract

Hip resurfacing arthroplasty is touted as an attractive alternative to total hip arthroplasty for treatment of severe joint pain and limited mobility in young patients because it is bone conserving and allows for a greater range of motion. There is concern in the orthopaedic community, however, regarding surgically-induced deformation of hip resurfacing cups. Cup deformation could potentially compromise the tight clearance between the femoral head and cup, resulting in increased wear, acoustic emissions, and joint binding. This phenomenon has been investigated both experimentally and with finite element analysis (FEA). Finite element studies have contributed significantly to our understanding of cup deformation, such as the effect of different cup dimensions on deformation results, but unfortunately such studies were deficient in a number of ways. The first objective of this thesis was to create a three-dimensional finite element model of resurfacing cup deformation that addressed the limitations of previous models pertaining to pelvic geometry, meshing, material properties, and cup insertion, in order to more fully elucidate cup deformation. The second objective was to demonstrate that two-dimensional characterization of cup deformation at the cup rim is insufficient, by more fully characterizing cup deformation in three-dimensions. The geometry was obtained via laser scanning and digital processing of a hemi-pelvis replica, meshing was performed without the use of shell elements, linear elasticity with strain-hardening after the onset of yielding was assigned to the cup and bone, and the most appropriate method for simulation of cup insertion was determined via two-dimensional axisymmetric analyses. Also, cup deformation was characterized in three-dimensions. The key findings of this thesis are that bone yield behaviour has important implications on press-fitting simulation, and the cup deforms irregularly and possibly plastically during press-fitting. A three-dimensional finite element model of resurfacing cup deformation that addressed the limitations of previous models was successfully created. Measurement of deformation at the rim of the resurfacing cup for characterization of cup deformation is insufficient; full characterization of cup deformation in three-dimensions is necessary. Future work should incorporate clinical testing to obtain model inputs such as impact and muscle forces, as well as model validation.