Fatigue Resistance Analysis of Tibial Baseplate in Total Knee Prosthesis - an in Vitro Biomechanical Study

Background Tibial baseplates were occasionally reported with clinical fatigue failures. This study postulated that tibial baseplate of a specific mobile bearing design with a uniform thickness across the baseplate offers more fatigue resistance than the fixed-bearing design. Tibial baseplates of a fixed bearing and a mobile bearing design were fatigue- tested in vitro to study their fatigue resistance. Methods. Five samples of each design were tested under a sinusoidal loading between 90 N and 900 N at 30 Hz till failure or 10 million cycles. Experimental setup followed a standard published test method. Scanning electron microscope was used for inspecting the fracture surface of the failed baseplate . Findings. Two baseplates of fixed bearing design failed before 10 million cycles. Fatigue crack advancement marks were visible on the fractured surface of the failed samples. The fractured cross-section showed that the failure started near the end of the fin, it was likely due to the stress concentration as stress singularity existed at a point of sudden geometrical change. Five mobile bearing baseplates passed the test. Design of the tibial baseplate without fin structure and with a uniform thickness across the whole baseplate could help reducing the incidence of fatigue failure. Interpretation. The prosthesis survival rate was influenced by the long-term integrity of the metallic part of the prostheses such as the tibial baseplate. This study revealed that the tibial baseplate of a mobile bearing design with a uniform thickness provided better fatigue resistance than fixed bearing one. Standardized fatigue screening of the tibial baseplate was considered important in designing knee prostheses. (c) 2005 Elsevier Ltd. All rights reserved

A probabilistic spatial dengue fever risk assessment by a threshold-based-quantile regression method.

Understanding the spatial characteristics of dengue fever (DF) incidences is crucial for governmental agencies to implement effective disease control strategies. We investigated the associations between environmental and socioeconomic factors and DF geographic distribution, are proposed a probabilistic risk assessment approach that uses threshold-based quantile regression to identify the significant risk factors for DF transmission and estimate the spatial distribution of DF risk regarding full probability distributions. To interpret risk, return period was also included to characterize the frequency pattern of DF geographic occurrences. The study area included old Kaohsiung City and Fongshan District, two areas in Taiwan that have been affected by severe DF infections in recent decades. Results indicated that water-related facilities, including canals and ditches, and various types of residential area, as well as the interactions between them, were significant factors that elevated DF risk. By contrast, the increase of per capita income and its associated interactions with residential areas mitigated the DF risk in the study area. Nonlinear associations between these factors and DF risk were present in various quantiles, implying that water-related factors characterized the underlying spatial patterns of DF, and high-density residential areas indicated the potential for high DF incidence (e.g., clustered infections). The spatial distributions of DF risks were assessed in terms of three distinct map presentations: expected incidence rates, incidence rates in various return periods, and return periods at distinct incidence rates. These probability-based spatial risk maps exhibited distinct DF risks associated with environmental factors, expressed as various DF magnitudes and occurrence probabilities across Kaohsiung, and can serve as a reference for local governmental agencies

Variations of Pseudo R-square across quantile levels of (a) the two most significant risk factors, and (b) the four most significant interaction effects.

<p>Variations of Pseudo R-square across quantile levels of (a) the two most significant risk factors, and (b) the four most significant interaction effects.</p

Comparison of pseudo R-squares across quantile levels among 1) conventional quantile regression model (CQR), 2) threshold-based quantile regression model (TBQR), and 3) threshold-based quantile regression considering interaction effects (TBQRI).

<p>Comparison of pseudo R-squares across quantile levels among 1) conventional quantile regression model (CQR), 2) threshold-based quantile regression model (TBQR), and 3) threshold-based quantile regression considering interaction effects (TBQRI).</p

Spatial distribution of average DF incidence rate in 535 Li's during 2004–2011.

<p>Spatial distribution of average DF incidence rate in 535 Li's during 2004–2011.</p

Map of Kaohsiung city and Fongshan district.

<p>Map of Kaohsiung city and Fongshan district.</p

The 95% confident intervals at the significant quantile levels for interaction effects between (a) canal and ditches, (b) canal and residential-business area, (c) canal and residential-other use area, (d) ditch and residential-business area, (e) ditch and residential-other use area, (f) pure residential area and residential-business area, (g) residential-business area and residential-other use area, and (h) residential-business area and per capita income, respectively.

<p>The 95% confident intervals at the significant quantile levels for interaction effects between (a) canal and ditches, (b) canal and residential-business area, (c) canal and residential-other use area, (d) ditch and residential-business area, (e) ditch and residential-other use area, (f) pure residential area and residential-business area, (g) residential-business area and residential-other use area, and (h) residential-business area and per capita income, respectively.</p

Spatial distribution of landuse factors important to DF across Kaohsiung-Fongshan area.

<p>Spatial distribution of landuse factors important to DF across Kaohsiung-Fongshan area.</p