Investigation into acetabular stress in total hip arthroplasty

Abstract

Total hip arthroplasty (THA) is a successful method for the treatment of a number of hip pathologies. In the UK between 2003 and 2016, the use of large femoral head sizes (32mm, 36mm) increased substantially in order to improve joint stability and reduce dislocation rates, whereas the use of the standard head size of 28mm decreased. This practice has been validated by findings that indicate lower dislocation rates when large heads are used. However, recently information published by the National Joint Registry for England, Wales, Northern Ireland and the Isle of Man (NJR) indicates that large head sizes appear to be associated with higher failure rates for cemented acetabular components. To date, research with regard to femoral head size in THA has been focused only to matters of joint stability, whereas the study of their effect on stress distribution has been neglected. This thesis describes an investigation into the effect of increasing femoral head size on the stresses of the acetabular cement mantle and pelvic bone for cemented acetabular components. The stress analysis was undertaken using a number of three-dimensional Finite Element (FE) models of an implanted cemented acetabular component. The models were created from computer tomography (CT) data of an artificial composited hemipelvis that was implanted with an all-polyethylene cemented acetabular component. The FE models were validated by comparing pelvic bone surface strains against experimental measurements obtained using Digital Image Correlation (DIC). Upon validation, a first analysis of the stresses in the acetabular cement mantle and pelvic bone was undertaken considering three femoral head sizes (28mm, 32mm, 36mm) and two loading scenarios; an average weight subject (70Kg) and an overweight subject (100Kg) undertaking a one leg stand. The models predicted a stress increase at the superior quadrants of the cortical bone-cement interface increased with femoral head diameter by up to 9%. In a second analysis of the acetabular cement mantle and pelvic bone stresses considered the impact of femoral head size (28mm, 32mm, 36mm), body weight and activity level. The models predicted an increase of stresses in the superior quadrants of the cortical bone-cement interface with increasing head size, patient weight and activity level. In stumbling, average von Mises stresses (22.4MPa) exceeded the bone cement yield strength for an obese subject (143kg) indicating that the cement mantle would fail, thus supporting the view of obesity and activity level as risk factors for aseptic loosening. In a third analysis the influence of osteoporosis on the pelvic bone and cement mantle stresses was evaluated considering the three head sizes (28mm, 32mm, 36mm) and the subjects of the second analysis for normal walking and descending stairs; the models predicted that stresses of osteoporotic cortical and trabecular bone were up to 33% and 50% higher than those of healthy bone. Also, the stresses at the cement interfaces where higher in the models with osteoporotic bone properties by up to 30%.

Date of Award	1 Aug 2020
Original language	English
Awarding Institution	The University of Manchester
Supervisor	M.T. Alonso-Rasgado (Supervisor) & Colin Bailey (Supervisor)