Edward D. Rothman

Anterior shoulder stability: Contributions of rotator cuff forces and the capsular ligaments in a cadaver model

The purpose of this study was to quantify in a biomechanical model the contributions to shoulder joint stability that are made by tensions in the four tendons of the rotator cuff and by static resistance of defined portions of the capsular ligaments. A materials testing machine was used to directly determine anterior joint laxity by measurement of the force required to produce a standard anterior subluxation. Shoulders were tested in external or neutral humeral rotation. Data were analyzed by multiway analysis of variance with regression analysis. This model simulated tensions in the rotator cuff musculature by applying static loads at the tendon insertion sites acting along the anatomic lines of action. A load in any of the cuff tendons resulted in a measurable and statistically significant contribution to anterior joint stability. The contributions between different tendons were not significantly different and did not depend on the humeral rotation (neutral or external). In neutral humeral rotation the superior and middle glenohumeral ligaments together function equally with the inferior glenohumeral ligament as primary stabilizers against anterior humeral translation. The posterior capsule is a secondary stabilizer. The external rotation of the abducted humerus increases anterior stability by more than doubling the stability contribution from the inferior glenohumeral ligament. The stability contribution from the posterior capsule is larger in external rotation than in neutral rotation but is still of secondary magnitude. In external rotation the stability contribution of the anterior capsule, including the superior glenohumeral ligament and the middle glenohumeral ligament, becomes insignificant. The model presented here simulates the combined effect of two major sources of shoulder stability. This versatile model permits the direct measurement of the contributions to anterior shoulder stability that are made by tensions in the rotator cuff tendons and by static resistance of defined capsular zones. The use of multiple regression analysis-a standard statistical technique but one relatively new to the orthopaedic literature-permits quantitative determination of the contribution of each independent variable to the dependent variable, shoulder stability.

Quantitative ultrasound backscatter for pulsed cavitational ultrasound therapy-histotripsy

Histotripsy is a well-controlled ultrasonic tissue ablation technology that mechanically and progressively fractionates tissue structures using cavitation. The fractionated tissue volume can be monitored with ultrasound imaging because a significant ultrasound backscatter reduction occurs. This paper correlates the ultrasound backscatter reduction with the degree of tissue fractionation characterized by the percentage of remaining normal-appearing cell nuclei on histology. Different degrees of tissue fractionation were generated in vitro in freshly excised porcine kidneys by varying the number of therapeutic ultrasound pulses from 100 to 2000 pulses per treatment location. All ultrasound pulses were 15 cycles at 1 MHz delivered at 100 Hz pulse repetition frequency and 19 MPa peak negative pressure. The results showed that the normalized backscatter intensity decreased exponentially with increasing number of pulses. Correspondingly, the percentage of normal appearing nuclei in the treated area decreased exponentially as well. A linear correlation existed between the normalized backscatter intensity and the percentage of normal appearing cell nuclei in the treated region. This suggests that the normalized backscatter intensity may be a potential quantitative real-time feedback parameter for histotripsy-induced tissue fractionation. This quantitative feedback may allow the prediction of local clinical outcomes, i.e., when a tissue volume has been sufficiently treated.

Type I collagen D-spacing in fibril bundles of dermis, tendon, and bone: bridging between nano- and micro-level tissue hierarchy.

Fibrillar collagens in connective tissues are organized into complex and diverse hierarchical networks. In dermis, bone, and tendon, one common phenomenon at the micrometer scale is the organization of fibrils into bundles. Previously, we have reported that collagen fibrils in these tissues exhibit a 10 nm width distribution of D-spacing values. This study expands the observation to a higher hierarchical level by examining fibril D-spacing distribution in relation to the bundle organization. We used atomic force microscopy imaging and two-dimensional fast Fourier transform analysis to investigate dermis, tendon, and bone tissues. We found that, in each tissue type, collagen fibril D-spacings within a single bundle were nearly identical and frequently differ by less than 1 nm. The full 10 nm range in D-spacing values arises from different values found in different bundles. The similarity in D-spacing was observed to persist for up to 40 μm in bundle length and width. A nested mixed model analysis of variance examining 107 bundles and 1710 fibrils from dermis, tendon, and bone indicated that fibril D-spacing differences arise primarily at the bundle level (∼76%), independent of species or tissue types.

Michigan hockey, meteoric precipitation, and rhythmicity of accumulation on peritidal carbonate platforms

On Saturday afternoon March 30, 1996, the University of Michigan hockey team won the 1996 National Collegiate Athletic Association Division I national championship. Durations between Wolverine goals, between opponent goals, and between all goals during the preceding 40-game regular season each describe an exponential distribution in which duration frequency depends only on number of shots on goal and probability of success. Compared to opponent scores, University of Michigan between-goal duration frequencies describe a trend having a steeper slope (University of Michigan shot better) and a higher intercept (University of Michigan took more shots). Over much of the past 100 yr, meteoric precipitation on Ann Arbor occurred during 11 949 days. Time durations of the 6401 precipitation episodes that occurred over this interval, as well as durations of contiguous days of precipitation and contiguous days of drought, each define an exponential distribution in which duration frequency is largely defined by total interval length (35 101 days) and probability of precipitation (34%). Roadcuts near Wytheville, Virginia, provide spectacular exposures of a 303.7-m-thick section of peritidal carbonate in the Middle to Upper Cambrian Elbrook and Conococheague Formations. Stratigraphic durations (thicknesses) of the 527 lithologic units within this sequence, of the 265 “cyclic” upward-shallowing lithofacies associations that can be designated over this interval, and of stratigraphic intervals between recurrences of like lithofacies, also define exponential distributions wherein frequency of stratigraphic recurrence is only dependent on the total thickness and net abundance of designated stratal elements. Frequency of goal scoring, and frequency and/or magnitude of meteoric precipitation can be described in terms of random, independent processes at short time scales. Similarly, exponential distributions of lithologic and “cyclic” thickness frequencies at Wytheville, Virginia (as well as in most other epicratonic peritidal sequences), indicate that meter-scale variation in carbonate deposition was predominantly controlled by stochastic (Poisson) processes that were largely unrelated to recurrent intrabasinal or extrabasinal forcing and/or to periodic (rhythmic) sediment accumulation.

Global geologic maps are tectonic speedometers—Rates of rock cycling from area-age frequencies

Relations among ages and present areas of exposure of volcanic, sedimentary, plutonic, and metamorphic rock units (lithosomes) record a complex interplay between depths and rates of formation, rates of subsequent tectonic subsidence and burial, and/or rates of uplift and erosion. Thus, they potentially serve as efficient deep-time geologic speedometers, providing quantitative insight into rates of material transfer among the principal rock reservoirs—processes central to the rock cycle. Areal extents of lithosomes exposed on all continents from two map sources (Geological Survey of Canada [GSC] and the Food and Agricultural Organization [FAO] of the United Nations Educational, Scientific, and Cultural Organization [UNESCO]) indicate that volcanic, sedimentary, plutonic, and metamorphic rocks occupy ~8%, 73%, 7%, and 12% of global exposures, respectively. Plots of area versus age of all mapped rock types display a power-law relation where ~6.5% of continental area is resurfaced with younger (~10% volcanic; 90% sedimentary) units every million years, and where areas of rock exposure decrease by ~0.86% for each 1% increase in outcrop age (r 2 = 0.90). Area-age relations for volcanic and sedimentary lithosomes are similar to the power-law distribution defined by all rock units (because ~81% of mapped area consists of these two lithologies) and reflect progressive decrease in amount of exposure with increasing age. Over the long term, continental surfaces are blanketed by new volcanic rocks and sediments at rates of ~1.5 and 12.1 × 10 6 km 2 /Ma, respectively. In contrast to power-law–distributed volcanic and sedimentary rocks that form at the Earth9s surface, age-frequency distributions for plutonic and metamorphic rocks exhibit lognormal relations, with modes at ca. 154 and 697 Ma, respectively. A dearth of younger exposures of plutonic and metamorphic rocks reflects the fact that these rock types form at depth, and some duration of tectonism is therefore required for their exposure. Increasing modal ages, from Quaternary for volcanic and sedimentary successions, to early Mesozoic for intrusive rocks, to Neoproterozoic for metamorphic rocks, demonstrate that greater amounts of geologic time are required for uplift to bring more deeply formed rocks to the Earth9s surface. The two different age-frequency distributions observed for these major rock types—a general power-law age distribution for volcanic and sedimentary rocks and a lognormal distribution for plutonic and metamorphic rock ages—reflect the interplay between depths of formation and mean rates of vertical tectonic displacement. Age-frequency distributions for each of the major rock types are closely replicated by a model that presumes that individual crustal elements behave as a large population of random walks in geologic time and crustal depth, and where the processes of surficial erosion associated with tectonic uplift serve to impose an absorbing boundary on this random-walk space. Comparisons between model-predicted age-frequencies and those apparent in global map data suggest that mean rates of crustal subsidence and uplift are approximately equal in magnitude, with mean rates of vertical tectonic diffusion of lithosomes from crustal depths of formation of about half a kilometer per million years. Rates of uplift and subsidence are strongly dependent on durations of tectonic dispersion (lithosome ages); however, mean rates on the order of hundreds of meters per million years suggested by map age-frequencies are the same as would be anticipated on the basis of hundreds of published rates of erosional uplift and exhumation determined by more conventional geochronometers. This agreement suggests that geologic maps serve as effective deep-time speedometers for the geologic rock cycle.

Evolution in Fine-Grained Environments. II. Habitat Selection as a Homeostatic Mechanism

A model of genotype specific habitat selection is developed for an organism subject to within-lifetime environmental fluctuations. Habitat selection is first overlaid upon both hard and soft selection Levene models with either discrete or continuous habitats. It is shown that even if all genotypes have identical physiological and fitness responses within a habitat, habitat selection can still maintain a polymorphism. In other words, physiological divergence is not a necessary prerequisite for divergence in habitat preferences. Within-lifetime environmental variability is then assumed to occur within each chosen habitat. It is shown that habitat selection acts as an evolutionary filter that can enhance the fitness impact of some niches and effectively eliminate the impact of others such that it generally increases the chances for a polymorphism under soft selection. However, density-dependent effects obscure the relationship between physiological fitness and evolutionary outcome. Indeed, it is possible for selection to favor an allele causing its bearers to preferentially go to the niche to which they are least physiologically adapted. Hence, changes in habitat preference can evolve before an organism has completely adapted physiologically to a new habitat. The titness impact of habitat selection interacts with both homeostatic avoidance mechanisms (i.e., short-term buffering) and with tolerance (long-term) mechanisms. In general, habitat selection will be most favored in those organisms deficient in long-term tolerance. Moreover, habitat selection tends to accentuate selection favoring short-term avoidance mechanisms. Thus, organisms displaying much habitat selection should have poor physiological long-term tolerances but effective physiological short-term avoidance mechanisms. Finally, if the fitness costs associated with habitat selection are too large to be ignored and are comparable for all genotypes, habitat selection directs the selective pressures back onto the physiological homeostatic capabilities. Hence, the very existence and extent of habitat selection depends critically upon the physiological capabilities of the organism.

The population genetics of parthenogenetic strains of Drosophila mercatorum : I. One locus model and statistics.

SummaryA one locus model has been developed to describe parthenogenetic populations restoring diploidy by central fusion, terminal fusion and gamete duplication. It was found that in the absence of selection all populations become homozygous. With selection, however, it is possible to maintain heterozygotes and homozygotes. The conditions required to yield such an equilibrium are a function of (1) the proportions of the various diploid restoring mechanisms (2) linkage to the kinetochore and (3) the intensity of selection. The model was then used to derive one-generation likelihood functions. These likelihoods were used in deriving estimation procedures for the frequency of gamete duplication which is important in forming isogenic lines and for the probability of a heterozygous female giving rise to a heterozygous zygoid. Next, n-generation likelihood functions with and without selection were calculated. These were used to estimate the selection coefficient and to derive two tests of the hypothesis of no selection versus the hypothesis of selection. The first test is a locally best test in the vicinity of no selection, and the second an “odds” for the hypotheses using a prior distribution on the selection coefficient.

Trends in Breast Cancer Screening: Impact of U.S. Preventive Services Task Force Recommendations.

INTRODUCTION Although there is general agreement among various guidelines on benefits of routine screening mammography, the age of screening initiation and the optimal frequency of the test remain controversial. In 2009, the U.S. Preventive Services Task Force (USPSTF) recommended against routine breast cancer screening in women aged younger than 50 years. In this study, screening mammography guideline adherence among U.S. women is explored by examining patterns in rates of mammography age of initiation and utilization in years prior to and following the 2009 USPSTF guideline implementation. METHODS U.S. population-based data from the 2007, 2008, 2010, and 2012 Behavioral Risk Factor Surveillance System surveys were used to measure the overall proportion and rate of change in the proportion of women who underwent screening mammography within the last year, by age and survey year. Data were accessed and analyzed in July 2014. RESULTS Rates of mammography screening were lower in 2010 and 2012 compared with 2007 and 2008 (p<0.0001). The rate of screening initiation at age 40 years increased over time and was the highest in the years following USPSTF guideline changes (p=0.012). CONCLUSIONS These data support no perceptible change in U.S. womens patterns of screening mammography age at initiation within 3 years of the USPSTF guideline revision. Whether this finding reflects a delayed effect of guideline revision in population trends or rather health provider practice and patient preference for more frequent screening is unclear and requires further investigation.

Complex rhythmicity of growth hormone secretion in humans.

To better characterize the 24 hr GH secretion pattern in humans, we studied frequently sampled 24 hr GH profiles in 93 young (18–45 years of age) healthy, fed volunteers: men (n = 67) and women (n = 26) with BMI<26kg/m2.Analysis of the composite GH series in men revealed 3 significant GH “waves” with peaks occurring at midnight (p < 0.0001), at noon (p < 0.02) and at 1800h (p < 0.0001). In women, similar pattern was seen, with three GH “waves” peaking at midnight (p < 0.0001), 1100h (p < 0.02) and at 1600h (p < 0.002).We conclude that the 24 hr rhythmicity of GH secretion is far more complex than currently appreciated. The attribution of the two daytime GH “waves” to food consumption is unlikely but cannot be excluded at the present time. The complex temporal pattern of pulsatile GH secretion may have important effects on regulation of target cell function.

Effect of registration on cyclical kinematic data.

Given growing interest in functional data analysis (FDA) as a useful method for analyzing human movement data, it is critical to understand the effects of standard FDA procedures, including registration, on biomechanical analyses. Registration is used to reduce phase variability between curves while preserving the individual curves shape and amplitude. The application of three methods available to assess registration could benefit those in the biomechanics community using FDA techniques: comparison of mean curves, comparison of average RMS values, and assessment of time-warping functions. Therefore, the present study has two purposes. First, the necessity of registration applied to cyclical data after time normalization is assessed. Second, we illustrate the three methods for evaluating registration effects. Masticatory jaw movements of 22 healthy adults (2 males, 21 females) were tracked while subjects chewed a gum-based pellet for 20s. Motion data were captured at 60 Hz with two gen-locked video cameras. Individual chewing cycles were time normalized and then transformed into functional observations. Registration did not affect mean curves and warping functions were linear. Although registration decreased the RMS, indicating a decrease in inter-subject variability, the difference was not statistically significant. Together these results indicate that registration may not always be necessary for cyclical chewing data. An important contribution of this paper is the illustration of three methods for evaluating registration that are easy to apply and useful for judging whether the extra data manipulation is necessary.