Contact finite element stress analysis of porous ingrowth acetabular cup implantation, ingrowth, and loosening

Two-dimensional linear and contact finite element analyses were conducted of total hip arthroplasty using metal-backed, porous ingrowth acetabular components. The stress transmission characteristics from the component to the surrounding bone were given special attention. Resultant loads of 20 and 40 degrees medial of vertical were studied, and the influence of adding a metal flange to the rim of the cup was evaluated. The results indicated that when a conventional metal-backed component (without a flange) is initially implanted and subjected to normal loading, these components may experience distraction between the component and the surrounding bone at inferior sites. Compressive stresses in the superior dome cancellous bone, however, will be substantial. If complete porous ingrowth is achieved, the superior dome compressive stresses will be reduced and substantial shear stresses created. In addition, high local bone stresses were found at the component rim. If bone ingrowth is achieved only in specific locations, stress transmission will be dictated by those locations and may differ markedly from the case of complete bone ingrowth. In the event that no porous ingrowth is achieved and a fibrous layer forms around the component, the interface stresses will be similar to those calculated for the natural hip. The addition of a flange to the rim of the cup will reduce the magnitude of the radial stresses transmitted to the cancellous bone superiorly and medially by directly transferring some of the load to the lateral wall of the pelvis. The flange will also help to relieve the high local stresses that are found at the component rim.     

The relationship of the transcutaneous oxygen tension, pulse waves and systolic pressures to the risk for limb amputation in patients with peripheral arterial disease and skin ulcers or gangrene.

AIM: Our aim was to determine how the risk associated with presence of low transcutaneous oxygen tension (tcPO2) for subsequent major amputation in patients with skin ulcers or gangrene and peripheral arterial disease, compares with the risks associated with low peripheral pressures and low amplitude of pulse waves. Secondly, we determined whether combination of measurements of oxygen tension with that of the pressures or pulse wave amplitude predicts amputation better than pressure, wave or oxygen tension measurements alone. METHODS: Measurements were carried out to obtain foot tcPO2, ankle and toe pressures, pressure indices, and toe pulse wave amplitude in 75 limbs with skin lesions and arterial disease of 66 patients referred to the vascular laboratory. These variables were related to the risk of a subsequent major amputation during a median time of 4.2 years, using Cox proportional hazards model. RESULTS: Low oxygen tension was associated with increased risk of amputation (relative risks 2.16 and 2.55 for tcPO2 < or = 10 mmHg and < or = 20 mmHg, respectively, P<0.05; relative risk 2.22 for tcPO2 < or = 30 mmHg, P=0.07). The relative risks associated with cutoff values of ankle and toe pressures and pressure indices varied from 2.53 (toe < or = 20 mmHg, P<0.05) to 5.83 (ankle < or = 50 mmHg, P<0.001) and the relative risk associated with low wave amplitude (< or = 4 mm) was 3.41, P<0.01. The cutoff values of tcPO2 became insignificant when included in the models together with each pressure variable or pulse amplitude separately. In contrast, wave amplitude remained significantly associated with increased risk of amputation after controlling for each pressure variable (P<0.05). CONCLUSIONS: TcPO2 < or = 10 mmHg and < or = 20 mmHg are related significantly to increased risk of amputation in patients with skin lesions and arterial disease, but these relative risks are similar in magnitude or smaller than those associated with low cutoff values of pressures, pressure indices or pulse wave amplitude. Low wave amplitude does provide significant information in addition to peripheral pressures with respect to the risk of amputation. On the other hand, low tcPO2 does not provide significant information in addition to peripheral pressures or pulse wave amplitude.     

Nine Years of the Freebase Cocaine Epidemic in the Bahamas

Nine years after the beginning of the epidemic of freebase (crack) cocaine abuse in the Bahamas, this historical study was done to characterize the natural course of the epidemic and to estimate the effectiveness of control measures. The authors' data include the incidence of new cases at the only psychiatric hospital in the Bahamas and at the primary community psychiatric clinic in the nation. The Bahamian response included 1) demand reduction, 2) supply reduction, and 3) reduction of money laundering. The annual number of new cases of crack abuse presenting for treatment declined from 1987 to mid-1991 in both facilities, but in 1992 it began rising again in the inpatient setting only. The changes in recent years have been accompanied by an increase in violent crimes against persons, especially robberies. (American Journal on Addictions 1994; 3:14–24)     

Structure-function studies in a series of carboxyl-terminal octapeptide analogues of anaphylatoxin C5a.

The synthesis and structure-activity relationships of C-terminal octapeptide analogues of anaphylatoxin C5a have been studied. The introduction of hydrophobic amino acids into the N-acetylated native octapeptide (N-Ac-His-Lys-Asp-Met-Gln-Leu-Gly-Arg-OH) (1) has led to an analogue with 100 times more activity than the native octapeptide in inhibiting the binding of 125I-labeled anaphylatoxin C5a to human neutrophil membrane receptors. The observed apparent binding Ki's for the compounds (8-10) are in the range of 1-3 microM, and they possess nearly full agonist activity, despite the fact that these analogues are one-eighth or -ninth the size of the natural ligand anaphylatoxin C5a.     

Balance algorithm for cluster randomized trials

Background  

Within cluster randomized trials no algorithms exist to generate a full enumeration of a block randomization, balancing for covariates across treatment arms. Furthermore, often for practical reasons multiple blocks are required to fully randomize a study, which may not have been well balanced within blocks.     

Assigning the source of human campylobacteriosis in New Zealand: A comparative genetic and epidemiological approach

Integrated surveillance of infectious multi-source diseases using a combination of epidemiology, ecology, genetics and evolution can provide a valuable risk-based approach for the control of important human pathogens. This includes a better understanding of transmission routes and the impact of human activities on the emergence of zoonoses. Until recently New Zealand had extraordinarily high and increasing rates of notified human campylobacteriosis, and our limited understanding of the source of these infections was hindering efforts to control this disease. Genetic and epidemiological modeling of a 3-year dataset comprising multilocus sequence typed isolates from human clinical cases, coupled with concurrent data on food and environmental sources, enabled us to estimate the relative importance of different sources of human disease. Our studies provided evidence that poultry was the leading cause of human campylobacteriosis in New Zealand, causing an estimated 58–76% of cases with widely varying contributions by individual poultry suppliers. These findings influenced national policy and, after the implementation of poultry industry-specific interventions, a dramatic decline in human notified cases was observed in 2008. The comparative-modeling and molecular sentinel surveillance approach proposed in this study provides new opportunities for the management of zoonotic diseases.