Delamination of a highly cross-linked polyethylene liner associated with titanium deposits on the cobalt-chromium modular femoral head following dislocation.

Retrieval studies of total hip replacements with highly cross-linked ultra-high-molecular-weight polyethylene liners have shown much less surface damage than with conventional ultra-high-molecular-weight polyethylene liners. A recent revision hip replacement for recurrent dislocation undertaken after only five months revealed a highly cross-linked polyethylene liner with a large area of visible delamination. In order to determine the cause of this unusual surface damage, we analysed the bearing surfaces of the cobalt-chromium femoral head and the acetabular liner with scanning electron microscopy, energy dispersive x-ray spectroscopy and optical profilometry. We concluded that the cobalt-chromium modular femoral head had scraped against the titanium acetabular shell during the course of the dislocations and had not only roughened the surface of the femoral head but also transferred deposits of titanium onto it. The largest deposits were 1.6 microm to 4.3 microm proud of the surrounding surface and could lead to increased stresses in the acetabular liner and therefore cause accelerated wear and damage. This case illustrates that dislocations can leave titanium deposits on cobalt-chromium femoral heads and that highly cross-linked ultra-high-molecular-weight polyethylene remains susceptible to surface damage.

Nanoindentation of soft hydrated materials for application to vascular tissues.

Soft hydrated materials, such as vascular tissues and other biomaterials, provide a number of challenges in the field of nanoindentation. However, the ability of nanoindentation to probe local, nanoscale mechanical properties of heterogeneous materials makes it desirable to adapt this technique for application to biologic tissues. To develop the field of nanoindentation for the analysis of soft hydrated materials, the goals of this study were fourfold: develop a sample hydration system, select an appropriate tip for soft material indentation, identify a substrate to be used for blunt tip alignment, and determine an appropriate control material for the development of future indentation protocols. A hydration system was developed that maintained sample hydration for over 8 h without completely submerging the sample. Further, a 100-microm radius of curvature conospherical tip was shown to be a suitable tip for indenting a variety of soft hydrated materials and back-illuminated agarose gel was found to be an effective material for use in tip alignment. Finally, agarose gel demonstrated similar qualitative and quantitative nanomechanical behavior to vascular tissue, suggesting that it will be an appropriate control material for the development of future indentation protocols for soft biologic tissues.

Comparative effects of two physical activity programs on measured and perceived physical functioning and other health-related quality of life outcomes in older adults.

BACKGROUND: Although inactivity is an important contributor to impaired functioning and disability with age, little is known concerning how improvements in physical functioning and well-being in older adults vary with the type of physical activity undertaken. METHODS: One hundred three adults age 65 years and older, recruited via population-based methods, were randomized to 12 months of community-based, moderate-intensity endurance and strengthening exercises (Fit & Firm) or stretching and flexibility exercises (Stretch & Flex). A combination of class- and home-based exercise formats was used. Measured and self-rated physical performance along with perceived functioning and well-being were assessed pre- and postintervention. RESULTS: Fit & Firm subjects showed greater 12-month improvements in both measured and self-rated endurance and strength compared to Stretch & Flex subjects. Stretch & Flex subjects reported greater improvements in bodily pain, and Stretch & Flex men evidenced greater improvements in flexibility relative to Fit & Firm subjects. Although overall exercise adherence was high in both exercise conditions (approximately 80%), subjects in both conditions showed better adherence to the home- versus class-based portions of their exercise prescriptions. CONCLUSIONS: Community-based programs focusing on moderate-intensity endurance and strengthening exercises or flexibility exercises can be delivered through a combination of formats that result in improvement in important functional and well-being outcomes. This represents one of the first studies to report significant improvements in an important quality of life outcome-bodily pain-with a regular regimen of stretching and flexibility exercises in a community-based sample of older adults.

Radiation and chemical crosslinking promote strain hardening behavior and molecular alignment in ultra high molecular weight polyethylene during multi-axial loading conditions.

The mechanical behavior and evolution of crystalline morphology during large deformation of eight types of virgin and crosslinked ultra high molecular weight polyethylene (UHMWPE) were studied using the small punch test and transmission electron microscopy (TEM). We investigated the hypothesis that both radiation and chemical crosslinking hinder molecular mobility at large deformations, and hence promote strain hardening and molecular alignment during the multiaxial loading of the small punch test. Chemical crosslinking of UHMWPE was performed using 0.25% dicumyl peroxide (GHR 8110, GUR 1020 and 1050), and radiation crosslinking was performed using 150 kGy of electron beam radiation (GUR 1150). Crosslinking increased the ultimate load at failure and decreased the ultimate displacement of the polyethylenes during the small punch test. Crosslinking also increased the near-ultimate hardening behavior of the polyethylenes. Transmission electron microscopy was used to characterize the crystalline morphology of the bulk material, undeformed regions of the small punch test specimens, and deformed regions of the specimens oriented perpendicular and parallel to the punch direction. In contrast with the virgin polyethylenes, which showed only subtle evidence of lamellar alignment, the crosslinked polyethylenes exhibited enhanced crystalline lamellae orientation after the small punch test, predominantly in the direction parallel to the punch direction or deformation axis. Thus, the results of this study support the hypothesis that crosslinking promotes strain hardening during multiaxial loading because of increased resistance to molecular mobility at large deformations effected by molecular alignment. The data also illustrate the sensitivity of large deformation mechanical behavior and crystalline morphology to the method of crosslinking and resin of polyethylene.

Evolution of morphology in UHMWPE following accelerated aging: the effect of heating rates.

Accelerated aging methods are used to evaluate the oxidative stability of UHMWPE components for total joint replacements. In this study, we traced the evolution of the crystalline morphology during accelerated thermal aging of UHMWPE in air with the intent of explaining previous, counterintuitive heating rate effects. GUR4150HP extruded rod stock material was machined into miniature (0.5 mm thick) specimens that were either gamma irradiated in air or in nitrogen (27 +/- 3 kGy) or left unirradiated (control). Accelerated aging in an air furnace (at 80 degrees C, atmospheric pressure) was performed on half of the test samples at a heating rate of 0.1 degrees C/min and at 5 degrees C/min for the remaining half. Although the initial heating rate, as measured by changes in density, did influence the absolute degradation rate by up to 214%, the heating rate effect did not appear to influence the relative ranking of UHMWPE in terms of its oxidative stability. The heating rate effect is more consistent with a kinetic mechanism of the oxidation process than it is with a previously hypothesized diffusion mechanism. UHMWPE morphology, as characterized using a transmission electron microscope (TEM), demonstrated considerable rearrangement of the crystalline regions as a result of the accelerated aging. The stacking of the lamellae observed after accelerated aging was not consistent with the morphology of naturally aged UHMWPE components. The observed differences in crystalline morphology likely result from the enhanced mobility of the polymer chains due to thermal aging and may be analogous to an annealing process.

Lifestyle activity. Current recommendations.

An accumulation of international scientific evidence indicates that physical inactivity is detrimental to health and that moderate levels of physical activity confer significant health benefits. Unfortunately, in countries where major surveys of physical activity have been conducted, the prevalence of sedentary behaviour has been found to be as high as 40%. In the US, where approximately 30% of adults report little or no physical activity, the Centers for Disease Control and the American College of Sports Medicine recently issued guidelines and recommendations on the amount and frequency of moderate levels of physical activity necessary to elicit health benefits in predominantly sedentary adults. These guidelines utilise a physical activity-health paradigm and, uniquely, recommend the potential effectiveness of activities of daily living or "lifestyle activity' for achieving health benefits. This article briefly reviews the rationale behind these guidelines and, in view of the historical association of the exercise training-fitness model to health, highlights some challenges and potential problems in applying these new guidelines to the general population.

Effects of a one-year high-intensity versus low-intensity resistance training program on bone mineral density in older women.

The purpose of this study was to determine the effects of a 12-month resistance training program, of two different intensities, on bone mineral density (BMD) in healthy, older women. Twenty-six Caucasian women (aged 65-79 years) completed the study. Subjects were randomly assigned to one of three groups: high-intensity (HI; n = 8), low-intensity (LI; n = 7), and control (CON; n = 11). The active groups performed 10 exercises, 3 days/week under supervision. Exercise intensity was maintained at 80% of one-repetition maximum (1-RM) for the HI groups, and at 40% 1-RM for the LI group. The volume of work was maintained constant between the two groups by assigning the LI group twice as many repetitions for each exercise. Maximal muscular strength and BMD of the lumbar spine and total hip were measured at baseline and at 12 months. Strength was evaluated using the 1-RM method, and BMD was determined by dual-energy X-ray absorptiometry. Exercise session attendance was similar for the two groups (81.0% HI; 76.8% LI). Muscular strength improved in the exercisers compared with the CON group (p < or = 0.05). Percentage change in lumbar spine BMD was 0.7 +/- 1.9%, 0.5 +/- 2.4%, and -0.1 +/- 2.3% for the HI, LI, and CON groups, respectively. Percentage change in total hip BMD was 0.8 +/- 2.3% (HI), 1.0 +/- 1.7% (LI), and 0.9 +/- 1.3% (CON). Group differences in BMD change were not significant (p > 0.05). These findings suggest that high-intensity and low-intensity resistance training regimens effectively increase muscular strength, but not lumbar spine or total hip BMD, in healthy, older women.

Weight-training effects on bone mineral density in early postmenopausal women.

We tested the hypothesis that weight training would be an effective modality in maintaining or increasing bone mineral density (BMD) at the lumbar spine, femoral neck, and bone mineral content (BMC) at the distal wrist in early postmenopausal women. A total of 17 women completed a 9 month weight-training program, and 9 women served as a control group. Resistance training occurred three times per week using exercises designed to increase muscular strength. Mean change in lumbar BMD in the weight-trained group (1.6 +/- 1.2%, mean +/- SEM) was significantly different from the change in the control group (-3.6 +/- 1.5%, p less than 0.01) over the 9 month period. No significant weight-training effect was detected at the femoral neck or distal wrist site. We conclude that weight training may be a useful exercise modality for maintaining lumbar BMD in early postmenopausal women.

Exercise and cardiovascular risk in black children.

The purposes of this study were to document the prevalence of cardiovascular disease risk factors in twenty black children to compare methods of measurement of blood pressure, body composition, and smoking; and to evaluate the effects of a ten week aerobic exercise training programme on blood pressure, cholesterol, smoking behaviour, and oxygen consumption. At pretest 25% of the children had blood pressures above the 90th percentile for their age or gender, 60% had a total cholesterol above 180 mg/dl and 35% exceeded 28% body fat. The mean difference score between systolic blood pressure and diastolic blood pressure measurements using a standard mercury sphygmomanometer and the Dinamap manometer was 1.5 (P less than 0.01) and 14.9 (P less than 0.0001) respectively. There was no significant difference in any of the methods used to measure body composition. Finally, there was no significant difference between the groups with regard to the dependent variables. Although the investigators identified the presence of elevated blood pressure, elevated total cholesterol, and obesity in this sample, the aerobic exercise training programme did not alter the risk profile. The authors urge caution in interpreting these results. Selection of the method for measurement of BP should be made with caution. A clear understanding of how each instrument works and its precision must be considered. Selection of the method for measurement of body composition can be based upon factors such as availability of equipment, cost, convenience, and subject preference.