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Title: The creep behaviour of polyethylmethacrylate based bone cements
Author: Venditti, N. P.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 1999
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Polymethylmethacrylate (PMMA) bone cement has been the most common choice for total hip replacement fixation for the last twenty five years. However, in recent years, it has fallen from favour with stem loosening and subsequent failure being attributed to fracture of the bone cement and bone necrosis. An alternative bone cement, polyethylmethacrylate (PEMA) is a more ductile material and is not as susceptible to brittle fracture. In addition, with a lower exotherm and monomer release rate the cement proves less damaging to the surrounding bone. Unfortunately, this material is inclined to creep, causing subsidence in the medullary canal. In an attempt to increase the creep resistance of the cement, hydroxyapatite particles can be added. The aim of this work was to undertake a thorough examination of the creep behaviour of a PEMA based bone cement, including the effects of curing regime, hydroxyapatite reinforcement, surrounding environment and ageing. Specimens were subjected to tensile creep tests at a number of temperatures, stresses and prior ageing times. Additionally, tests were performed to establish the effects on the creep properties of hydroxyapatite reinforcement. Ageing was found to increase the creep resistance with time, and therefore must play a vital role in the prediction of creep. This effect, as well as the effects of temperature and applied stress appeared relatively unchanged irrespective of testing environment. However, water based environments produced the lowest creep resistance in the PEMA cement and were therefore chosen as the worse case scenario. Hydroxyapatite reinforcement acted to increase the creep resistance, with creep compliance values for 25% reinforced samples being half that of unfilled cement at 1 million seconds. Predictions of the creep behaviour were made employing the effective time theory and time temperature superposition as well as those based on mathematical models. Both methods gave close matching predictions up to two decades beyond the testing times. At creep times up to three years the predictions show that if this material is to be used for joint replacements, hydroxyapatite reinforcement is not just beneficial but essential.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available