Method to analyse the fatigue damage in acrylic bone cement

Acrylic bone cement is a poly(methyl methacrylate)-based material that ensures short-term stability of orthopedic implants after surgery. Its long-term performance can be affected by many factors (e.g., composition, cement mixing and delivery method, temperature, humidity). Furthermore, patient activities produce a spectrum of cyclic loads that generate microdamage within the acrylic bone cement mantle. Therefore, pre-clinical studies on fatigue damage of acrylic bone cements are essential for predicting the long-term stability of cemented implants. There are several methods for analyzing damage of acrylic bone cement. However, they present a number of limitations. The aim of this study was to validate the use of a high-resolution scanner to analyze the presence of microcracks in acrylic bone cement. The proposed method met predetermined criteria to overcome limitations of previous methods, ensuring approximate spatial resolution of 5 microns, reduction of image acquisition time, and reduction of artifacts due to operator and/or environment during image acquisition. Additionally, the described method was applied to three types of acrylic bone cement specimens that previously were subjected to a fatigue test. The presented method enables the accurate assessment of fatigue damage induced during cycling loading, including quantification of the number, length, type and position of cement cracks

The effect of vacuum mixing and pre-heating the femoral component on the mechanical properties of the cement mantle

We investigated the effect of pre-heating a femoral component on the porosity and strength of bone cement, with or without vacuum mixing used for total hip replacement. Cement mantles were moulded in a manner simulating clinical practice for cemented hip replacement. During polymerisation, the temperature was monitored. Specimens of cement extracted from the mantles underwent bending or fatigue tests, and were examined for porosity. Pre-heating the stem alone significantly increased the mean temperature values measured within the mantle (+14.2 degrees C) (p < 0.001) and reduced the mean curing time (-1.5 min) (p < 0.001). The addition of vacuum mixing modulated the mean rise in the temperature of polymerisation to 11 degrees C and reduced the mean duration of the process by one minute and 50 seconds (p = 0.01 and p < 0.001, respectively). In all cases, the maximum temperature values measured in the mould simulating the femur were < 50 degrees C. The mixing technique and pre-heating the stem slightly increased the static mechanical strength of bone cement. However, the fatigue life of the cement was improved by both vacuum mixing and pre-heating the stem, but was most marked (+ 280 degrees C) when these methods were combined. Pre-heating the stem appears to be an effective way of improving the quality of the cement mantle, which might enhance the long-term performance of bone cement, especially when combined with vacuum mixing

Effect of stem preheating on the fatigue behaviour of bone cement around hip prostheses

Tensile fatigue behaviour of bone cement specimens obtained from cement mantles moulded in vitro, simulating the surgical scenario, was investigated. The effect of stem preheating, before its insertion into the cement dough, on specimen fatigue life was studied. A commercial bone cement was selected for this study. Bone cement mixing was conducted in air, following the manufacturer's instructions, and injected simulating the clinical practice. Two conditions were considered: stem maintained at the surgical room temperature (23 degrees C), and stem preheated to 45 degrees C. Four repetitions of the whole procedure were performed for each condition obtaining a total of 32 specimens. All specimens underwent fatigue testing (stress ratio, 0; maximum tensile stress, 15 MPa) until failure. Both two-parameter and three-parameter Weibull distributions were initially used to analyse the fatigue life data set. However, the two-parameter distribution was chosen for both groups on the basis of the coefficient of determination used to test the goodness of fit. Stem preheating seems to have a negligible effect on fatigue behaviour of the studied bone cement in the low range of fatigue lives (up to 10(4)). However, above this number of cycles, stem preheating seems to reduce the probability of failure. These findings are discussed in the text

Fracture properties of an acrylic bone cement

This study investigated experimentally the fracture properties, i.e., the fatigue strength, the resistance to crack propagation and the fracture toughness, of an acrylic bone cement (Cemex RX). The mean endurance limit was determined following the staircase method. The endurance limit was estimated at 9.2 MPa. The fatigue crack propagation rate was measured according to the ASTM E647 standard. The equation of the line fitting the crack growth per cycle (da/dN) versus the stress-intensity factor range (delta K), in a log-log graph, was used to calculate the empirical constants of Paris' law for the selected bone cement: da/dN (m/cycle) = 3.56 x 10(-7) x delta K (MPa x m1/2)5.79. This power-law relationship described well (R2 = 0.96) the growth rate in the stable crack growth region, i.e., in the mid delta K range. The fracture toughness K(IC) of the bone cement was determined according to the ASTM E399 standard. The K(IC) mean value was 1.38 MPa x m1/2. These experimental results provide the set of necessary inputs for numerical studies aimed to investigate the damage accumulation process in the mantle fixing cemented prostheses

Fracture properties of an acrylic bone cement

This study investigated experimentally the fracture properties, i.e., the fatigue strength, the resistance to crack propagation and the fracture toughness, of an acrylic bone cement (Cemex RX). The mean endurance limit was determined following the staircase method. The endurance limit was estimated at 9.2 MPa. The fatigue crack propagation rate was measured according to the ASTM E647 standard. The equation of the line fitting the crack growth per cycle (da/dN) versus the stress-intensity factor range (delta K), in a log-log graph, was used to calculate the empirical constants of Paris' law for the selected bone cement: da/dN (m/cycle) = 3.56 x 10(-7) x delta K (MPa x m1/2)5.79. This power-law relationship described well (R2 = 0.96) the growth rate in the stable crack growth region, i.e., in the mid delta K range. The fracture toughness K(IC) of the bone cement was determined according to the ASTM E399 standard. The K(IC) mean value was 1.38 MPa x m1/2. These experimental results provide the set of necessary inputs for numerical studies aimed to investigate the damage accumulation process in the mantle fixing cemented prostheses

Assessment of implant stability of cementless hip prostheses through the frequency response function of the stem-bone system

Cementless joint prostheses require adequate initial press-fitting to achieve sufficient primary stability, which is necessary for bone ingrowth and implant success. A device was developed that measured intra-operatively the stability of a hip stem in the host bone. It included an excitatory piezoelectric system based on a ceramic multilayer bender, which delivered a controlled excitation in the range 1200\u20132000 Hz to the prosthesis. An accelerometer mounted on the host bone measured the transmitted vibration so as to identify the resonance frequency. Resonance frequency (and its associated shift) was measured immediately after implant press-fitting, and while a torque was applied to the implant. The proposed method was validated in vitro on 5 femurs covering a wide range of bone quality. Each bone was tested with different degrees of implant press-fitting. Implant stability estimated with the vibration method was compared against implant\u2013bone micromotions that were measured simultaneously by a displacement transducer during this validation session. A strong correlation was found between the shift of the resonance frequency caused by load application, and implant stability. A quantitative threshold was identified that enabled consistently discriminating stable implants form quasi-stable ones: when the resonance frequency shifted less than 5Hz during torque application, the residual micromotion after load removal was always less than 150micron

Initiation in the Puerto Rican Novel

285 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1982.Initiation, or the rites and ordeals that mark the passage from adolescence into adulthood, has appeared in most genres of literature through the ages. In this study I examine the presence of the elements of initiation in the Puerto Rican novel. It is my intent to prove that a relationship can be established between the appearance and usage of initiation and the colonial status of Puerto Rico.I use a combination of two critical approaches: archetypal and socio-historical. By integrating these two critical methods, I create a prototype of initiation within a Puerto Rican context. This serves as a guide for the study of initiation in the individual novels. For my investigation I have selected three novels: La v(')ispera del hombre (1959) by Rene Marques, Ardiente suelo, fr(')ia estacion (1961) by Pedro Juan Soto, and El fuego y su aire (1970) by Enrique A. Laguerre.It is the presence of initiatory elements in each of these novels that provides them with a structural link. The works are also joined by the treatment of themes such as ethnicity, language, identity, and acculturation. Despite the differences in style and content, all three novels reflect the concern of the authors regarding Puerto Rico's future and her present colonial status.This dissertation is divided into five chapters. Chapter I contains an overview of Puerto Rico in terms of history, culture, society, language and other related topics. I investigate the causes of the Island's colonial condition and show how it still exists despite the changes in the last four decades. In Chapter II the steps of initiation are presented and explained, along with their application and relevance in modern literature and life. Chapters III, IV and V contain the examination of the individual novels presented in chronological order.Each of the three literary chapters includes general background information on the author and his works, a short analysis of the fictional and structural components of the novel and a detailed examination of the elements of initiation and their relationship to the colonial status of Puerto Rico.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD