1,721,015 research outputs found
Comparative Raman study on the molecular structure and IN VIVO wear of poly(methyl methacrylate)-based devices used as temporary knee prostheses: Effect of the antibiotic
No full textThe infection rate of total knee arthroplasty is still high, in spite of the high success of this surgical procedure. The use of an antibiotic-loaded temporary spacer made of poly(methyl methacrylate) (PMMA) has been proposed to treat infected knee arthroplasties. This study was aimed at comparatively investigating, on a molecular scale, two types of spacers from the same manufacturer (Spacer K and Vancogenx-space knee, Tecres, Italy), which differ for the added antibiotic (gentamicin sulphate in Spacer K and gentamicin sulphate + vancomycin hydrochloride in Vancogenx). Raman spectroscopy was used to gain more insights into the possible effects of the antibiotic on the spacer composition and polymer structure both in the new components and after in vivo use. Vancogenx was found to contain a lower residual MMA content than Spacer K (about 0.15% versus 0.4%). The former contained a higher amount of isotactic stereosequences than the latter, while the syndiotactic content (the prevailing component) was not significantly different in the two prostheses. The presence of vancomycin hydrochloride influenced not only the degree of polymerization and PMMA tacticity and crystallinity, but in turn also the wear behavior. Actually, Spacer K retrievals were found more affected by in vivo implantation than Vancogenx-space knee ones, revealing slight variations in polymer tacticity and crystallinity and relative radiopacifier content, besides release of MMA and additives of polymerization. However, these changes did not appear worrisome, due to the temporary nature of the prosthesis. In view of these results, the addition of vancomycin hydrochloride could offer an advantage, in spite of the higher costs requested and the potential risks of its unselective use
Metal transfer evaluation on ceramic biocomponents: A protocol based on 3D scanners
No full textTitanium signs frequently appear on femoral heads coupled with metal back acetabular components, after dislocation or repositioning of total hip arthroplasties. These metallic deposits, called metal transfer, are a significant clinical phenomenon because they can affect the resistance and tribological performance of the prosthesis. The quantification and the study of position of the metal transfer extent over a prosthesis surface is a scientific problem to be addressed to design more effective replacements. This paper proposes a new protocol to evaluate the metal transfer amount, employing 3D optical scanners, and reverse engineering software. The technique allows the assessment of metal transfer rates, absolute areal coverage, and position of the metal deposits by acquiring the 3D digital colored model of the hip ball surfaces with high-precision 3D scanners, and separating the regions with metallic depositions by 3D mesh processing. Results permit to evaluate effects on the tribological behavior of the synovial biobearing
Does the addition of vitamin E to conventional UHMWPE improve the wear performance of hip acetabular cups? Micro-raman characterization of differently processed polyethylene acetabular cups worn on a hip joint simulator
Full text linkIn knee replacements, vitamin E-doped ultra-high molecular weight polyethylene (UHMWPE) shows a better wear behavior than standard UHMWPE. Therefore, different sets of polyethylene (PE) acetabular cups, i.e. standard UHMWPE and cross-linked polyethylene irradiated with 50 kGy and 75 kGy, were compared, at a molecular level, with vitamin E-doped UHMWPE to evaluate their wear performance after being tested on a hip joint simulator for five million cycles. Unworn control and worn acetabular cups were analyzed by micro-Raman spectroscopy to gain insight into the effects of wear on the microstructure and phase composition of PE. Macroscopic wear was evaluated through mass loss measurements. The data showed that the samples could be divided into two groups: 1) standard and vitamin E-doped cups (mass loss of about 100 mg) and 2) the crosslinked cups (mass loss of about 30–40 mg). Micro-Raman spectroscopy disclosed different wear mechanisms in the four sets of acetabular cups, which were related to surface topography data. The vitamin E-doped samples did not show a better wear behavior than the cross-linked ones in terms of either mass loss or morphology changes. However, they showed lower variation at the morphological level (lower changes in phase composition) than the UHMWPE cups, thus confirming a certain protecting role of vitamin E against microstructural changes induced by wear testing
Integrated friction measurements in hip wear simulations: Short-term results
No full textHip joint wear simulators are used extensively to simulate the dynamic behaviour of the human hip joint and, through the wear rate, gain a concrete indicator about the overall wear performance of different coupled bearings. Present knowledge of the dynamic behaviour of important concurrent indicators, such as the coefficient of friction, could prove helpful for the continuing improvement in applied biomaterials.
A limited number of commercial or custom-made simulators have been designed specifically for friction studies but always separately from wear tests; thus, analysis of these two important parameters has remained unconnected.
As a result, a new friction sensor has been designed, built, and integrated in a commercial biaxial rocking motion hip simulator. The aim of this study is to verify the feasibility of an experimental set-up in which the dynamic measurement of the friction factor could effectively be implemented in a standard wear test without compromising its general accuracy and repeatability.
A short wear test was run with the new set-up for 1x10(6) cycles. In particular, three soft-bearings (metal-on-polyethylene, Phi=28 mm) were tested; during the whole test, axial load and frictional torque about the vertical loading axis were synchronously recorded in order to calculate the friction factor. Additional analyses were performed on the specimens, before and after the test, in order to verify the accuracy of the wear test.
The average friction factor was 0.110 +/- 0.025. The friction sensors showed good accuracy and repeatability throughout. This innovative set-up was able to reproduce stable and reliable measurements. The results obtained encourage further investigations of this set-up for long-term assessment and using different combinations of materials
Meniscal wear at a three-component total ankle prosthesis by a knee joint simulator
No full textDespite the fundamental value of wear simulation studies to assess wear resistance of total joint replacements, neither specialised simulators nor established external conditions are available for the human ankle joint. The aim of the present study was to verify the suitability of a knee wear simulator to assess wear rates in ankle prostheses, and to report preliminary this rate for a novel three-component total ankle replacement design. Four intact 'small' size specimens of the Box ankle were analysed in a four-station knee wear simulator. Special component-to-actuator holders were manufactured and starting spatial alignment of the three-components was sought. Consistent load and motion cycles representing conditions at the ankle joint replaced exactly with the prosthesis design under analysis were taken from a corresponding mechanical model of the stance phase of walking. The weight loss for the three specimens, after two million cycles, was 32.68, 14.78, and 62.28 mg which correspond to a linear penetration of 0.018, 0.008, and 0.034 mm per million-cycle, respectively for the specimens #1, #2, and #3. The knee wear simulator was able to reproduce load-motion patterns typical of a replaced ankle. Motion of the meniscal bearing in between the tibial and talar components was smooth, this component remaining in place and in complete congruence with the metal components throughout the test
CMM-based procedure for polyethylene non-congruous Unicompartmental Knee Prosthesis wear assessment
No full textOne of the most recent advances in knee replacement Surgery is the Unicompartmental Knee Prosthesis that involves the substitution of only one compartment. Uncertainties on the survivorship of such design led to the improvement of pre-clinical mechanical simulation. To effectively support this market phase with clinically relevant wear data it is important to be able to accurately quantify it and the consequent knee prostheses functionality.
The aim of the present study was to validate a coordinate-measuring machine (CMM)-based procedure to assess the wear of a commercially available, non-congruous UKP design after mechanical simulation; gravimetric quantification of material defeat produced, in fact, a reference wear value.
The two methods are in good agreement (R(2) = 0.73) even if CMM technique systematically overestimates the measured values.
Material behavior has been monitored through out the test to be able to distinguish, within dimensional changes, permanent plastic deformations and creep contribution.
In the case of simulator test mean linear and gravimetric wear rate were evaluated, respectively, 0.19 +/- 0.02 mm and 0.86 +/- 0.15 mg/Mc.
Our findings encouraged further work on reliability and accuracy improvement
Multivariable approach for wear evaluation on long term hip implants retrievals: preliminary results
No full textRoughness digital characterization and influence on wear of retrieved knee components
No full textTribological performance of knee components are strongly related to the surface character-istics. Primarily, the roughness and its 3D distribution on the surfaces affect the joint performance. One of the main limitations related to the tribological study of knee prostheses is that most of the research studies report in vitro or in silico results, as knee retrievals are difficult to find or are too damaged to be analyzed. This paper is focused on the roughness characterization of retrieved metal femoral components of total knee replacements (TKR) by means of a rugosimeter and involving digital methods to reconstruct the 3D topography of the studied surfaces. The aim of this study is to investigate how changes and distribution of roughness are correlated between the medial vs. the lateral part and how the resulting digital topography can give insights about the wear behavior
- …
