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PubMed2005

[The development and biomechanical testing of a femoral press fit fixation for hamstring tendons].

PURPOSE: The purpose of this study was to investigate press fit femoral fixation of hamstring tendons and to compare the mechanical properties with press fit patellar tendon bone (PTB) fixation. METHODS: The PTB and hamstring tendons of 30 human cadavers (age: 55.8+/-18.0 years) were used as grafts. An outside-in press fit fixation with a knot in the semitendinosus and gracilis graft (SG-K) and an inside-out (SG-BI) and an outside-in fixation (SG-BO) with the tendons looped over a bone block were compared with a bone-patellar tendon (PT) press fit fixation in 30 bovine femora. The angle between the direction of force and bone tunnel was 60 degrees. The constructs underwent 20 cycles of loading between 60 and 260 N. Constructs were loaded until failure at a speed of 1 mm/sec. Graft fixation was analyzed in terms of maximum load to failure, stiffness and elongation during cyclic stretching. A video analysis of length changes was investigated. RESULTS: There was a significant difference in the maximum load to failure. The SG-BI fixation was inferior to the other three techniques (Mann-WhitneyU-test, P<0.01). There was no difference in stiffness between the techniques. Length changes of PT-fixation from the first to the fifth loading cycle were significantly smaller compared with all other groups (0.73+/-0.58 mm). There was no significant difference between the groups from the 15th to the 20th cycle of cyclic loading. CONCLUSIONS: Press fit fixation of hamstring grafts is technically challenging. However, pull-out forces for SG-O and SG-K were equivalent to BPT-graft fixation. Adequate preconditioning for all hamstring tendon press fit techniques is crucial.

Anterior Cruciate Ligament↗
PubMed2000

Adaptive walks by the fittest among finite random mutants on a Mt. Fuji-type fitness landscape. II. Effect of small non-additivity.

We examined properties of adaptive walks by the fittest on "rough Mt. Fuji-type" fitness landscapes, which are modeled by superposing small uncorrelated random component on an additive fitness landscape. A single adaptive walk is carried out by repetition of the evolution cycle composed of (1) mutagenesis process that produces random d-fold point mutants of population size N and (2) selection process that picks out the fittest mutant among them. To comprehend trajectories of the walkers, the fitness landscape is mapped into a (x, y, z)-space, where x, y and z represent, respectively, normalized Hamming distance from the peak on the additive fitness landscape, scaled additive fitness and scaled nonadditive fitness. Thus a single adaptive walk is expressed as the dynamics of a particle in this space. We drew the "hill-climbing" vector field, where each vector represents the most probable step for a walker in a single step. Almost all of the walkers are expected to move along streams of vectors existing on a particular surface that overlies the (x, y)-plane, toward the neighborhood of a characteristic point at which a mutation-selection-random drift balance is reached. We could theoretically predict this reachable point in the case of random sampling search strategy.

Biological Evolution↗
PubMed2006

The effect of bone tunnel dilation versus extraction drilling on the initial fixation strength of press-fit anterior cruciate ligament reconstruction.

INTRODUCTION: Serial dilation of the bone tunnel has been reported to create a tighter graft-tunnel fit. It was hypothesized that a serial dilation of the femoral bone tunnel would increase the initial fixation strength in press-fit anterior cruciate ligament (ACL) reconstructive surgery. MATERIALS AND METHODS: Initial fixation strength of the femoral press-fit fixation technique was investigated in 72 porcine specimens in an ex vivo study by varying the femoral tunnel preparation technique. Extraction-drilling, tunnel dilation by 1 mm and dilation by 2.5 mm were assessed. Initial fixation strength of press-fit fixated patellar tendon-bone grafts was tested within each preparation group conducting a single cycle (and cyclic) load to failure protocol. The resulting tunnel diameter and the porcine femoral bone mineral density were determined using microradiographs and peripheral quantitative CT scans, respectively. RESULTS: Dilating a previously extraction-drilled femoral bone tunnel by 1 mm significantly enhances initial press-fit fixation strength in both single cycle and cyclic load to failure testing when compared to extraction-drilling and tunnel dilation by 2.5 mm. Due to an initial spring-back effect the resulting diameter of the femoral tunnel was underestimated by 3.3% with drilling and 6.7 and 12.2% with dilation by 1 and 2.5 mm, respectively. Volumetric trabecular bone mineral density at the site corresponding to the area of tunnel placement averaged 318 mg/cm(3). CONCLUSION: Dilating a femoral tunnel that is underdrilled by 1 mm appears to be a reasonable technical procedure in order to enhance initial fixation strength of press-fit ACL graft fixation.

Analysis of Variance↗
PubMed2007

Implications of deep electrode insertion on cochlear implant fitting.

Using long Med-El Combi40+ electrode arrays, it is now possible to cover the whole range of the cochlea, up to about two turns. Such insertion depths have received little attention. To evaluate the contribution of deeply inserted electrodes, five Med-El cochlear implant users were tested on vowel and consonant identification tests with fittings with first one, two, and up to five apical electrodes being deactivated. In addition, subjects performed pitch-ranking experiments, using loudness-balanced stimuli, to identify electrodes creating pitch confusions. Radiographs were taken to measure each electrode insertion depth. All subjects used each modified fitting for two periods of about 3 weeks. During the experiment, the same stimulation rate and frequency range were maintained across all the fittings used for each individual subject. After each trial period the subject had to perform three consonant and three vowel identification tests. All subjects showed deep electrode insertions ranging from 605 degrees to 720 degrees. The two subjects with the deepest electrode insertions showed significantly increased vowel- and consonant-identification performances with fittings with the two or three most apical electrodes deactivated compared to their standard fitting with all available electrodes activated. The other three subjects did not show significant improvements in performance when one or two of their most apical electrodes were deactivated. Four out of five subjects preferred to continue use of a fitting with one or more apical electrodes deactivated. The two subjects with the deepest insertions also showed pitch confusions between their most apical electrodes. Two possible reasons for these results are discussed. One is to reduce neural interactions related to electrodes producing pitch confusions. Another is to improve the alignment of the frequency components of sounds coded by the electrical signals delivered to each electrode to the overall pitch of the auditory perception produced by the electrical stimulation of auditory nerve fibers.

Adult↗
PubMed2006

Fitness effects of Wolbachia and Spiroplasma in Drosophila melanogaster.

Maternally inherited endosymbionts that manipulate the reproduction of their insect host are very common. Aside from the reproductive manipulation they produce, the fitness of these symbionts depends in part on the direct impact they have on the female host. Although this parameter has commonly been investigated for single infections, it has much more rarely been established in dual infections. We here establish the direct effect of infection with two different symbionts exhibiting different reproductive manipulation phenotypes, both alone and in combination, in the fruit fly Drosophila melanogaster. This species carries a cytoplasmic incompatibility inducing Wolbachia and a male-killing Spiroplasma, occurring as single or double (co-) infections in natural populations. We assessed direct fitness effects of these bacteria on their host, by comparing larval competitiveness and adult fecundity of uninfected, Wolbachia, Spiroplasma and Wolbachia-Spiroplasma co-infected females. We found no effect of infection status on the fitness of females for both estimates, that is, no evidence of any benefits or costs to either single or co-infection. This leads to the conclusion that both bacteria probably have other sources of benefits to persist in D. melanogaster populations, either by means of their reproductive manipulations (fitness compensation from male death in Spiroplasma infection and cytoplasmic incompatibility in Wolbachia infection) or by positive fitness interactions on other fitness components.

Animals↗
PubMed2006

Fitting experimental data to models that use morphological data from public databases.

Ideally detailed neuron models should make use of morphological and electrophysiological data from the same cell. However, this rarely happens. Typically a modeler will choose a cell morphology from a public database, assign standard values for Ra, Cm, and other parameters and then do the modeling study. The assumption is that the model will produce results representative of what might be obtained experimentally. To test this assumption we developed models of CA1 hippocampal pyramidal neurons using 4 different morphologies obtained from 3 public databases. The multiple run fitter in NEURON was used to fit parameter values in each of the 4 morphological models to match experimental data recorded from 19 CA1 pyramidal cells. Fits with fixed standard parameter values produced results that were generally not representative of our experimental data. However, when parameter values were allowed to vary, excellent fits were obtained in almost all cases, but the fitted parameter values were very different among the 4 reconstructions and did not match standard values. The differences in fitted values can be explained by very different diameters, total lengths, membrane areas and volumes among the reconstructed cells, reflecting either cell heterogeneity or issues with the reconstruction data. The fitted values compensated for these differences to make the database cells and experimental cells more similar electrotonically. We conclude that models using fully reconstructed morphologies need to be calibrated with experimental data (even when morphological and electrophysiological data come from the same cell), model results should be generated with multiple reconstructions, morphological and experimental cells should come from the same strain of animal at the same age, and blind use of standard parameter values in models that use reconstruction data may not produce representative experimental results.

Action Potentials↗
PubMed2005

Physical activity, cardiorespiratory fitness, and their relationship to cardiovascular risk factors in African Americans and non-African Americans with above-optimal blood pressure.

This report describes cross-sectional associations among physical activity, cardiorespiratory fitness, dietary habits, and cardiovascular disease (CVD) risk factors in a large sample (n = 810) of African Americans (n = 279) and non-African Americans (n = 531) with above-optimal blood pressure. Participants in PREMIER, a clinical trial for blood pressure control through lifestyle approaches, underwent baseline assessments to determine physical activity level, cardiorespiratory fitness category, dietary intake, and CVD risk factors. Mean levels of body mass index (BMI), total cholesterol, LDL cholesterol, HDL cholesterol, daily percent calories from fat and saturated fat, daily servings of fruits and vegetables, and daily fiber intake were examined across three physical activity levels and two fitness categories. Hypertension status was also assessed. Data were stratified by sex and ethnicity. For all participants, those in the low fitness category had higher BMI levels. Total cholesterol was lower in African American women in the high fitness category. Mean values of more than five daily servings of fruits and vegetables were reported by non-African American women and African American men in the high activity category. Higher intake of dietary fiber was found for non-African American women at the high activity level, with a similar trend observed for African American women. Future work examining these associations prospectively should include sufficient minority representation to enhance generalizability to all population groups and determine the beneficial effects from increased physical activity and improved cardiorespiratory fitness.

Adult↗
PubMed1987

Strains and micromotions of press-fit femoral stem prostheses.

Average femoral geometry was determined from sections of 25 human femurs. A 'stem design program' was used to determine the largest femoral stem that could be introduced into the canal. The stem was fine tuned by observations of fit in Plexiglass models of the 25 femurs. This stem was called the 'Exact-Fit'. Type 1 stem was formed by grinding the anterior and posterior faces flat. Type 2 stem was formed by additionally grinding the medial and lateral faces flat. Four fresh femurs were used for the experiments. Strain gages were located on the proximal medial area and level with the distal lateral tip. Displacement transducers were mounted proximally to measure stem-bone micromotion. Vertical and anterior-posterior forces were applied to the femoral head and normal strain data obtained. The stems were then inserted in sequence and the strains and micromotions were measured. After the uncemented stems had been tested, a smaller size of 'exact-fit' stem was cemented and the tests repeated. The strains with the uncemented stems were closer to normal than with the cemented stems. For example, compressive calcar strains averaged 56% of normal uncemented compared with 30% cemented for the different loadings. The micromotion was higher uncemented, but was still at a low level. The 'exact-fit' stem gave less resultant micromotion than the type 1 and type 2 stems. The high variation of the strain results was attributed to variations in stem-bone contact and fit. The study provided information of direct application to press-fit stems in hip replacement surgery.

Bone Cements↗
PubMed1994

The analysis of survival (mortality) data: fitting Gompertz, Weibull, and logistic functions.

Survival functions are fitted to survival data from several large populations. The Gompertz survival function corresponds to exponential mortality rate increases with time. The Weibull survival function corresponds to mortality rates that increase as a power function of time. A two-parameter, logistic survival function is introduced, and corresponds to mortality rates that increase, and then decrease, with time. A three-parameter logistic-mortality function also is examined. It reflects mortality rates that rise, and then plateau, with age. Data are from published studies of medflies, Drosophila, house flies, flour beetles, and humans. Some survival data are better fit by a logistic survival function than by the more traditionally used Gompertz or Weibull functions. Gompertz, Weibull, or logistic survival functions often fit the survival of 95+% of a population, and the 'tails' of the survival curves usually appear to fall between the values predicted by the three functions. For some populations, such 'tails' appear to be too complex to be fit well by any simple function. Survival data for males and females in some populations are best fit by different functions. Populations of 100 or more are needed to distinguish among the functions. When testing effects of environmental or genetic manipulations on survival, it has been common to determine the changes in parameter values for a given function, such as Gompertz. It may be equally important to determine whether the best-fit function has changed as well.

Animals↗
PubMed1991

A short history of occupational fitness and health promotion.

The suggestion of a linkage between adequate exercise and occupational health dates back to Ramazzini's classical observations on cobblers and tailors. However, excessive hours of work at too high an intensity were of greater concern than increase of fitness or health promotion in the early phases of the industrial revolution. Loss of physical condition is a more recent phenomenon, and it can be traced to automation in industry and the home, progressive urbanization, and widespread use of the automobile. The Canadian government has seen worksite fitness and health promotion programs as convenient tactics to reverse this trend. Exercise programs apparently yield a healthier and more effective labor force, and major corporations have thus followed the government's lead in developing fitness and health promotional facilities as a part of personnel or occupational health departments. Some health economists have suggested a substantial return upon such investment, but most corporations still regard the promotion of fitness and a healthy lifestyle as an expression of good citizenship. Currently, unifocal fitness programs are being replaced by modular health programs that address a wide range of lifestyle issues, including nutrition, stress relaxation, cigarette addiction, and drug abuse. The purpose of the present brief review is to trace from a personal perspective the development of an interest in employee fitness as an important component of occupational health programs over the past 300 years. The linkage of this phenomenon to the changing human demands of the worksite will also be explored.

Canada↗
PubMed2004

Long-term porous-coated cup survivorship using spikes, screws, and press-fitting for initial fixation.

This study examined the long-term outcome of a single institution's experience with 4,289 primary total hip arthroplasties using hemispheric porous-coated cups. Initial fixation was achieved with spikes (255 AML TriSpike cups), by press-fitting with rim screws (427 Arthropor cups) or by press-fitting the component (83 Harris-Galante, 391 ACS Triloc+, 2,537 Duraloc, and 596 Pinnacle cups). Among 203 revised hips, only 18 cups were found to be loose at the time of revision. Using revision for any reason as an end point, 15-year survivorship was 82.9% +/- 5.6% (95% confidence interval) for spiked components, 71.6% +/- 8.5% for press-fit cups with adjunctive rim screws, and 72.0% +/- 12.6% for press-fit components (P<.001, log rank). Using revision for aseptic loosening as an end point, 15-year survivorship was 94.7% +/- 3.4% for spiked cups, 98.4% +/- 1.9% for press-fit cups with screws and 100% +/- 0.1% for press-fit cups. Despite an increasing incidence of polyethylene wear-related revisions, porous-coated acetabular components have demonstrated excellent long-term fixation.

Acetabulum↗
PubMed2006

A meta-regression to examine the relationship between aerobic fitness and cognitive performance.

Many studies have been conducted to test the potentially beneficial effects of physical activity on cognition. The results of meta-analytic reviews of this literature suggest that there is a positive association between participation in physical activity and cognitive performance. The design of past research demonstrates the tacit assumption that changes in aerobic fitness contribute to the changes in cognitive performance. Therefore, the purpose of this meta-analysis was to use meta-regression techniques to statistically test the relationship between aerobic fitness and cognitive performance. Results indicated that there was not a significant linear or curvilinear relationship between fitness effect sizes (ESs) and cognitive ESs for studies using cross-sectional designs or posttest comparisons. However, there was a significant negative relationship between aerobic fitness and cognitive performance for pre-post comparisons. The effects for the cross-sectional and pre-post comparisons were moderated by the age group of the participants; however, the nature of this effect was not consistent for the two databases. Based on the findings of this meta-analytic review, it is concluded that the empirical literature does not support the cardiovascular fitness hypothesis. To confirm the findings of this review, future research should specifically test the dose-response relationship between aerobic fitness and cognitive performance. However, based upon the findings of this review, we also encourage future research to focus on other physiological and psychological variables that may serve to mediate the relationship between physical activity and cognitive performance.

Adolescent↗
PubMed2004

Diaphragms in clinical trials: is clinician fitting necessary?

BACKGROUND: The need for fitting a contraceptive diaphragm has recently been questioned in the context of upcoming trials in which the ability of the diaphragm to prevent sexually transmitted infections will be tested. Being able to provide the same size device to all women would greatly simplify supplying the device and training the clinicians, provided that it does not compromise effectiveness. METHODS: Data from studies of Lea's Shield and FemCap, in which all women were sized for a standard diaphragm and half were randomized to use it during the studies, were reanalyzed to determine if it was feasible to give all women in a barrier study the same size diaphragm or, alternatively, to determine if diaphragm size could be predicted using an algorithm of one or more parameters. RESULTS: If all women received a size 70 diaphragm, rather than being fitted by a clinician, 33.2% would receive the same size that they would have received if they had been fitted by a clinician. If the definition of a "correct" fit were broadened to include one size larger or smaller than what the clinician would have prescribed, 78.0% would be "correctly" fitted. Using an algorithm that considered parity, body weight and other factors did not improve results. CONCLUSION: It would be acceptable to conduct a trial in which all women receive a size 70 diaphragm, provided that all women are sized; that safety, effectiveness and acceptability are closely monitored and that study results are stratified by the diaphragm size determined by clinician fitting. It would also be informative to use sized diaphragms as the comparator in studies of new single-size devices.

Body Weight↗
PubMed2006

Viral fitness can influence the repertoire of virus variants selected by antibodies.

Minority genomes in the mutant spectra of viral quasispecies may differ in relative fitness. Here, we report experiments designed to evaluate the contribution of relative fitness to selection by a neutralizing monoclonal antibody (mAb). We have reconstructed a foot-and-mouth disease virus (FMDV) quasispecies, with two matched pairs of distinguishable mAb-escape mutants as minority genomes of the mutant spectrum. Each mutant of a pair differs from the other by 11-fold or 33-fold in relative fitness. Analysis of the mutant spectra of virus populations selected with different concentrations of antibody in infections in liquid culture medium has documented a dominance of the high fitness counterpart in the selected population. Plaque development as a function of increasing concentration of the antibody has shown that each mutant of a matched pair yielded the same number of plaques, although the high fitness mutant required less time for plaque formation, and attained a larger plaque size at any given time-point. This result documents equal intrinsic resistance to the antibody of each mutant of a matched pair, confirming previous biochemical, structural, and genetic studies, which indicated that the epitopes of each mutant pair were indistinguishable regarding reactivity with the monoclonal antibody. Thus, relative viral fitness can influence in a significant way the repertoire of viral mutants selected from a viral quasispecies by a neutralizing antibody. We discuss the significance of these results in relation to antibody selection, and to other selective forces likely encountered by viral quasispecies in vivo.

Amino Acid Sequence↗
PubMed2026

Exploring an Intermediate Colorectal Cancer Screening Test Based on Stool Proteomics and Machine Learning for Optimizing the Selection of Patients for Colonoscopy Identified From FIT.

The fecal immunochemical test (FIT) for detecting fecal occult blood, used alone or in combination with other stool biomarkers, has been demonstrated to be effective in the context of colorectal cancer (CRC) screening programs. However, FIT yields a significant proportion of false positives leading to unnecessary colonoscopies. In this study, we have investigated whether leftover FIT stool samples could be repurposed for proteomics analysis as a triage step for patients before recommending colonoscopy. High-throughput mass spectrometry analyses on a set of 141 FIT-positive samples (50 controls with no lesion, 45 with advanced adenomas and 46 with CRC) in combination with machine learning tools were used. Results showed that with a specificity &#x2265;90%, a large proportion of the false FIT positives could be identified thus providing an efficient strategy for reducing unnecessary colonoscopies. Furthermore, CRC cases were also precisely predicted to be true positives, thus providing an approach for prioritizing patients for colonoscopy. In conclusion, this study demonstrates the feasibility of using proteomics for analysis of leftover FIT stool samples as an intermediate step to triage patients selected for colonoscopy in CRC screening programs.

Humans↗
PubMed2004

What is wrong with absolute individual fitness?

One of the most basic facts about evolution is that fitness is a relative concept. It does not matter how well an organism survives and reproduces, only that it does so better than other organisms bearing alternative traits. Nevertheless, many evolutionary arguments are framed in terms of absolute individual fitness. The absolute fitness criterion (AFC) can be justified in terms of relative fitness only given certain assumptions that are frequently violated in nature. In particular, interactions must occur in groups that are randomly formed and phenotypic variation among groups must be tightly coupled to genetic variation. Complicating the genotype-phenotype relationship can cause phenotypic variation among groups to become nonrandom, even when the groups are randomly formed, favoring traits that do not maximize absolute individual fitness. Complex genotype-phenotype relationships and complex population structures require explicit models of evolutionary change based on relative fitness differences within and among groups.

Journal Article↗
PubMed2005

Saddle pressure measuring: validity, reliability and power to discriminate between different saddle-fits.

Saddle-fit is recognised as an important factor in the pathogenesis of back problems in horses and is empirically being evaluated by pressure measurements in clinical practice, although not much is known about the validity, reliability and usability of these devices in the equine field. This study was conducted to assess critically a pressure measurement system marketed for evaluating saddle fit. Validity was tested by calculating the correlation coefficient between total measured pressure and the weight of 28 different riders. Reliability and discriminative power with respect to different saddle fitting methods were evaluated in a highly standardised, paired measurement set-up in which saddle-fit was quantified by air-pressure values inside the panels of the saddle. Total pressures under the saddle correlated well with riders' weight. A large increase in over-day sensor variation was found. Within trial intra-class correlation coefficients (ICCs) were excellent, but the between trial ICCs varied from poor to excellent and the variation in total pressure was high. In saddles in which the fit was adjusted to individual asymmetries of the horse, the pressure measurement device was able to detect correctly air-pressure differences between the two panels in the back area of the saddle, but not in the front area. The device yielded valid results, but was only reliable in highly standardised conditions. The results question the indiscriminate use of current saddle pressure measurement devices for the quantitative assessment of saddle-fit under practical conditions and suggest that further technical improvement may be necessary.

Animal Husbandry↗
PubMed2003

An investigation of the suitability of bra fit in women referred for reduction mammaplasty.

Reduction mammaplasty is rationed in NHS plastic surgery provision, despite abundant evidence that most women who undergo this operation obtain significant improvement in their physical health and quality of life. We suspected that women seeking reduction mammaplasty often wear ill-fitting bras, which may exacerbate some of their symptoms. Therefore, we studied 103 women who attended a nurse-run pre-assessment clinic, asking them what size bra they currently wore and then measuring them to see whether their bra size was correct. We also questioned bra manufacturers, designers and shop bra fitters about bra manufacture, sizing and fitting techniques, and we reviewed these findings. Of the 102 women suitable for inclusion in the study, all wore the wrong size bra. Their mean 'claimed' back measurement was 36 inches (range: 30-42 in.) and their mean cup size was F (range: C-J). We found that all but one underestimated their back measurement (by a mean of 4 in.; range: -2-10 in.) and overestimated their cup size (by a mean of three sizes; range: one size smaller to seven sizes larger) when compared with manufacturers' fitting guidelines. Multiple regression analysis used to assess the relationships of various factors to incorrect bra sizing showed a strong link (Pearson correlation=0.54; P<0.001) between obesity and inaccurate back measurement. The reasons why women with breast hypertrophy wear incorrectly fitting bras are discussed. We conclude that obesity, breast hypertrophy, fashion and bra-fitting practices combine to make those women who most need supportive bras the least likely to get accurately fitted bras, so exacerbating the symptoms for which they seek surgery.

Adolescent↗