Cardiac q-space trajectory imaging by motion-compensated tensor-valued diffusion encoding in human heart in vivo

PURPOSE

Tensor-valued diffusion encoding can probe more specific features of tissue microstructure than what is available by conventional diffusion weighting. In this work, we investigate the technical feasibility of tensor-valued diffusion encoding at high b-values with q-space trajectory imaging (QTI) analysis, in the human heart in vivo.

METHODS

Ten healthy volunteers were scanned on a 3T scanner. We designed time-optimal gradient waveforms for tensor-valued diffusion encoding (linear and planar) with second-order motion compensation. Data were analyzed with QTI. Normal values and repeatability were investigated for the mean diffusivity (MD), fractional anisotropy (FA), microscopic FA (μFA), isotropic, anisotropic and total mean kurtosis (MKi, MKa, and MKt), and orientation coherence (Cc ). A phantom, consisting of two fiber blocks at adjustable angles, was used to evaluate sensitivity of parameters to orientation dispersion and diffusion time.

RESULTS

QTI data in the left ventricular myocardium were MD = 1.62 ± 0.07 μm2 /ms, FA = 0.31 ± 0.03, μFA = 0.43 ± 0.07, MKa = 0.20 ± 0.07, MKi = 0.13 ± 0.03, MKt = 0.33 ± 0.09, and Cc  = 0.56 ± 0.22 (mean ± SD across subjects). Phantom experiments showed that FA depends on orientation dispersion, whereas μFA was insensitive to this effect.

CONCLUSION

We demonstrated the first tensor-valued diffusion encoding and QTI analysis in the heart in vivo, along with first measurements of myocardial μFA, MKi, MKa, and Cc . The methodology is technically feasible and provides promising novel biomarkers for myocardial tissue characterization.

Accuracy and Precision of a Novel Photogate System to Measure Toe Clearance on Stairs

Background: Toe clearance on stairs is typically measured using optoelectronic systems, though these are often constrained to the laboratory, due to their complex setups. Here we measured stair toe clearance through a novel prototype photogate setup and compared this to optoelectronic measurements. Methods: Twelve participants (age 22 ± 3 years) completed 25 stair ascent trials, each on a seven-step staircase. Toe clearance over the fifth step edge was measured using Vicon and the photogates. Twenty-two photogates were created in rows through laser diodes and phototransistors. The height of the lowest photogate broken at step-edge crossing was used to determine photogate toe clearance. A limits of agreement analysis and Pearson's correlation coefficient compared the accuracy, precision and relationship between systems. Results: We found a mean difference of -1.5 mm (accuracy) between the two measurement systems, with upper and lower limits (precision) of 10.7 mm and -13.8 mm, respectively. A strong positive correlation was also found (r = 70, n = 12, p = 0.009) between the systems. Discussion: The results suggest that photogates could be an option for measuring real-world stair toe clearances, where optoelectronic systems are not routinely used. Improvements to the design and measurement factors may help to improve the precision of the photogates.

Spring-mass behavioural adaptations to acute changes in prosthetic blade stiffness during submaximal running in unilateral transtibial prosthesis users

BACKGROUND

Individuals with lower-limb amputation can use running specific prostheses (RSP) that store and then return elastic energy during stance. However, it is unclear whether varying the stiffness category of the same RSP affects spring-mass behaviour during self-selected, submaximal speed running in individuals with unilateral transtibial amputation.

RESEARCH QUESTION

The current study investigates how varying RSP stiffness affects limb stiffness, running performance, and associated joint kinetics in individuals with a unilateral transtibial amputation.

METHODS

Kinematic and ground reaction force data were collected from eight males with unilateral transtibial amputation who ran at self-selected submaximal speeds along a 15 m runway in three RSP stiffness conditions; recommended habitual stiffness (HAB) and, following 10-minutes of familiarisation, stiffness categories above (+1) and below (-1) the HAB. Stance-phase centre of mass velocity, contact time, limb stiffness' and joint/RSP work were computed for each limb across RSP stiffness conditions.

RESULTS

With increased RSP stiffness, prosthetic limb stiffness increased, whilst intact limb stiffness decreased slightly (p<0.03). Centre of mass forward velocity during stance-phase (p<0.02) and contact time (p<0.04) were higher in the intact limb and lower in the prosthetic limb but were unaffected by RSP stiffness. Intact limb hip joint positive work increased for both the +1 and -1 conditions but remained unchanged across conditions in the prosthetic limb (p<0.02).

SIGNIFICANCE

In response to changes in RSP stiffness, there were acute increased mechanical demands on the intact limb, reflecting a reliance on the intact limb during running. However, overall running speed was unaffected, suggesting participants acutely adapted to an RSP of a non-prescribed stiffness.

Using a stair horizontal-vertical illusion to increase foot clearance over an inconsistently taller stair-riser

Introduction

Stair falls can be caused by inconsistent stair dimensions. During ascent, inconsistently taller stair risers lead to reduced foot clearances as the inconsistency goes unnoticed. A stair horizontal-vertical illusion increases perceived riser heights and foot clearance and could offset reduced foot clearances over inconsistently taller risers, though this might impact other stair safety measures.

Method

Twelve participants (age: 22 (3) years) ascended a seven-step staircase under three conditions: i) all steps consistent in riser height (consistent), ii) a 1cm increase in step 5 riser height (inconsistent) and iii) a 1cm increase in step 5 riser height, superimposed with a stair horizontal-vertical illusion (illusion). Vertical foot clearance, foot overhang, and margins of stability were assessed over step 4, 5 and 6. Perceived riser height due to the illusion was determined through a computer perception test. A One-Way Repeated Measures ANOVA compared biomechanical variables between conditions. A One Sample t test compared perceived riser height to the true height.

Results

Over the inconsistent step 5, foot clearance reduced by 0.8cm compared to consistent. Illusion increased foot clearance by 1.1cm and decreased foot overhang by 4% compared to inconsistent. On step 4 the illusion led to more anterior instability compared to inconsistent. Illusion and inconsistent led to more mediolateral stability compared to consistent. The illusion increased perceived riser height by 12%.

Discussion

Foot clearance reductions over inconsistently taller risers can be offset by a stair horizontal-vertical illusion. Additional benefits included a safer foot overhang and unaffected stability over the inconsistent riser. Changes to step 4 stability might have resulted from leaning forward to look at the step 5 illusion. The stair horizontal-vertical illusion could be a practical solution for inconsistently taller stair risers, where a rebuild is usually the only solution.

The next step in optimising the stair horizontal-vertical illusion: Does a perception-action link exist in older adults?

INTRODUCTION

Tripping on stairs results from insufficient foot to step edge clearance and can often lead to a fall in older adults. A stair horizontal-vertical illusion is suggested to increase the perceived riser height of a step and increase foot clearance when stepping up. However, this perception-action link has not been empirically determined in older adults. Previous findings suggesting a perception-action effect have also been limited to a single step or a three-step staircase. On larger staircases, somatosensory learning of step heights may be greater which could override the illusory effect on the top step. Furthermore, the striped nature of the existing stair horizontal-vertical illusion is associated with visual stress and may not be aesthetically suitable for use on public stairs. These issues need resolving before potential future implementation on public stairs.

METHODS

Experiment 1. A series of four computer-based perception tests were conducted in older (N = 14: 70 ± 6 years) and young adults (N = 42: 24 ± 3 years) to test the influence of different illusion designs on stair riser height estimation. Participants compared images of stairs, with horizontal-vertical illusions or arbitrary designs on the bottom step, to a plain stair with different bottom step riser heights and selected the stair they perceived to have the tallest bottom riser. Horizontal-vertical illusions included a previously developed design and versions with modified spatial frequencies and mark space ratios. Perceived riser height differences were assessed between designs and between age groups. Experiment 2. To assess the perception-action link, sixteen older (70 ± 7 years) and fifteen young (24 ± 3 years) adults ascended a seven-step staircase with and without horizontal-vertical illusions tested in experiment 1 placed onto steps one and seven. Foot clearances were measured over each step. To determine whether changes in perception were linked to changes in foot clearance, perceived riser heights for each horizontal-vertical illusion were assessed using the perception test from experiment 1 before and after stair ascent. Additional measures to characterise stair safety included vertical foot clearance, margins of stability, foot overhang, stair speed, and gaze duration, which were assessed over all seven steps.

RESULTS

Experiment 1. All horizontal-vertical illusion designs led to significant increases in the perceived riser height in both young and older adults (12-19% increase) with no differences between age groups. Experiment 2. On step 7, each horizontal-vertical illusion led to an increase in vertical foot clearance for young (up to 0.8 cm) and older adults (up to 2.1 cm). On step 1 significant increases in vertical foot clearance were found for a single horizontal-vertical illusion when compared to plain (1.19 cm increase). The horizontal-vertical illusions caused significant increases in the perceived riser height (young; 13% increase, older; 11% increase) with no differences between illusion design, group or before and after stair ascent. No further differences were found for the remaining variables and steps.

CONCLUSION

Results indicate a perception-action link between perceived riser height and vertical foot clearance in response to modified versions of the horizontal-vertical illusion in both young and older adults. This was shown with no detriment to additional stair safety measures. Further evaluating these illusions on private/public stairs, especially those with inconsistently taller steps, may be beneficial to help improve stair safety for older adults.

Influence of step-surface visual properties on confidence, anxiety, dynamic stability, and gaze behaviour in young and older adults

BACKGROUND

Step-surface visual properties are often associated with stair falls. However, evidence for decorating stairs typically concerns the application of step-edge highlighters rather than the entire step-surface. Here we examine the influence of step-surface visual properties on stair descent safety, with a view to generating preliminary evidence for safe stair décor.

METHODS

Fourteen young (YA: 23.1 ± 3.7 years), 13 higher (HAOA: 67 ± 3.5) and 14 lower (LAOA: 73.4 ± 5.7) ability older adults descended a seven-step staircase. Older adults were stratified based on physiological/cognitive function. Step-surface décor patterns assessed were: Black and white (Busy); fine grey (Plain); and striped multicolour (Striped); each implemented with/without black edge-highlighters (5.5 cm width) totalling six conditions. Participants descended three times per condition. Confidence was assessed prior to, and anxiety following, the first descent in each condition. 3D kinematics (Vicon) quantified descent speed, margin of stability, and foot clearances with respect to step-edges. Eye tracking (Pupil-labs) recorded gaze. Data from three phases of descent (entry, middle, exit) were analysed. Linear mixed-effects models assessed within-subject effects of décor (×3) and edge highlighters (×2), between-subject effects of age (×3), and interactions between terms (α = p < .05).

RESULTS

Décor: Plain décor reduced anxiety in all ages and abilities (p = .032, effect size: g_av = 0.3), and increased foot clearances in YA and HAOA in the middle phase (p < .001, g_av = 0.53), thus improving safety. In contrast, LAOA exhibited no change in foot clearance with Plain décor. Patterned décor slowed descent (Busy: p < .001, g_av = 0.2), increased margins of stability (Busy: p < .001, g_av = 0.41; Striped: p < .001, gav = 0.25) and reduced steps looked ahead (Busy: p = .053, gav = 0.25; Striped: p = .039, gav = 0.28) in all ages and abilities. This reflects cautious descent, likely due to more challenging conditions for visually extracting information about the spatial characteristics of the steps useful to guide descent. Edge highlighters: Step-edge highlighters increased confidence (p < .001, g_av = 0.53) and reduced anxiety (p < .001, g_av = 0.45) in all ages and abilities and for all décor, whilst removing them slowed descent in HAOA (p = .01, g_av = 0.26) and LAOA (p = .003, g_av = 0.25). Step-edge highlighters also increased foot clearance in YA and HAOA (p = .003, g_av = 0.14), whilst LAOA older adults showed no adaptation. No change in foot clearances with décor or step-edge highlighters in LAOA suggests an inability to adapt to step-surface visual properties.

CONCLUSION

Patterned step surfaces can lead to more cautious and demanding stair negotiation from the perspective of visually extracting spatial information about the steps. In contrast, plain décor with step edge highlighters improves safety. We therefore suggest plain décor with edge highlighters is preferable for use on stairs.

Jaguar (Panthera onca) density and tenure in a critical biological corridor

We estimated jaguar density and tenure, and investigated ranging behavior, using camera traps across the Maya Forest Corridor, a human-influenced landscape in central Belize that forms the only remaining connection for jaguar populations inhabiting two regional forest blocks: the Selva Maya and the Maya Mountain Massif. Jaguars were ubiquitous across the study area. Similar to the neighboring Selva Maya, mean density ranged from 1.5 to 3.1 jaguars per 100 km2, estimated by spatial capture-recapture models. Cameras detected almost twice as many males as females, probably reflecting detection bias, and males ranged more widely than females within the camera grid. Both sexes crossed two major rivers, while highway crossings were rare and male-biased, raising concern that the highway could prevent female movement if traffic increases. Jaguars were more transient where the landscape was fragmented with settlements and agriculture than in contiguous forest. Compared with jaguars in the protected forests of the Maya Mountains, jaguars in central Belize displayed a lower potential for investment in intraspecific communication, indicative of a lower quality landscape; however, we did detect mating behavior and juveniles. Tenure of individuals was shorter than in the protected forests, with a higher turnover rate for males than females. At least three-quarters of reported jaguar deaths caused by people were male jaguars, and the majority was retaliation for livestock predation. Jaguars seem relatively tolerant to the human-influenced landscape of central Belize. However, intensification of game hunting and lethal control of predators would threaten population persistence, while increased highway traffic and clear-cutting riparian forest would severely limit the corridor function. Our results show that the viability of the corridor, and thus the long-term survival of jaguar populations in this region, will depend on appropriate land-use planning, nonlethal control of livestock predators, enforcement of game hunting regulations, and wildlife-friendly features in future road developments.

Children With Developmental Coordination Disorder Show Altered Visuomotor Control During Stair Negotiation Associated With Heightened State Anxiety

Safe stair negotiation is an everyday task that children with developmental coordination disorder (DCD) are commonly thought to struggle with. Yet, there is currently a paucity of research supporting these claims. We investigated the visuomotor control strategies underpinning stair negotiation in children with (N = 18, age = 10.50 ± 2.04 years) and without (N = 16, age = 10.94 ± 2.08 years) DCD by measuring kinematics, gaze behavior and state anxiety as they ascended and descended a staircase. A questionnaire was administered to determine parents' confidence in their child's ability to safely navigate stairs and their child's fall history (within the last year). Kinematics were measured using three-dimensional motion capture (Vicon), whilst gaze was measured using mobile eye-tracking equipment (Pupil labs). The parents of DCD children reported significantly lower confidence in their child's ability to maintain balance on the stairs and significantly more stair-related falls in the previous year compared to the parents of typically developing (TD) children. During both stair ascent and stair descent, the children with DCD took longer to ascend/descend the staircase and displayed greater handrail use, reflecting a more cautious stair negotiation strategy. No differences were observed between groups in their margin of stability, but the DCD children exhibited significantly greater variability in their foot-clearances over the step edge, which may increase the risk of a fall. For stair descent only, the DCD children reported significantly higher levels of state anxiety than the TD children and looked significantly further along the staircase during the initial entry phase, suggesting an anxiety-related response that may bias gaze toward the planning of future stepping actions over the accurate execution of an ongoing step. Taken together, our findings provide the first quantifiable evidence that (a) safe stair negotiation is a significant challenge for children with DCD, and that (b) this challenge is reflected by marked differences in their visuomotor control strategies and state anxiety levels. Whilst it is currently unclear whether these differences are contributing to the frequency of stair-related falls in children with DCD, our findings pave the way for future research to answer these important questions.

Children With Developmental Coordination Disorder Exhibit Greater Stepping Error Despite Similar Gaze Patterns and State Anxiety Levels to Their Typically Developing Peers

This study examined stepping accuracy, gaze behavior, and state-anxiety in children with (N = 21, age M = 10.81, SD = 1.89) and without (N = 18, age M = 11.39, SD = 2.06) developmental coordination disorder (DCD) during an adaptive locomotion task. Participants walked at a self-selected pace along a pathway, placing their foot into a raised rectangular floor-based target box followed by either no obstacles, one obstacle, or two obstacles. Stepping kinematics and accuracy were determined using three-dimensional motion capture, whilst gaze was determined using mobile eye-tracking equipment. The children with DCD displayed greater foot placement error and variability when placing their foot within the target box and were more likely to make contact with its edges than their typically developing (TD) peers. The DCD group also displayed greater variability in the length and width of their steps in the approach to the target box. No differences were observed between groups in any of the gaze variables measured, in mediolateral velocity of the center of mass during the swing phase into the target box, or in the levels of self-reported state-anxiety experienced prior to facing each task. We therefore provide the first quantifiable evidence that deficits to foot placement accuracy and precision may be partially responsible for the increased incidence of trips and falls in DCD, and that these deficits are likely to occur independently from gaze behavior and state-anxiety.

Individuals with unilateral transtibial amputation exhibit reduced accuracy and precision during a targeted stepping task

Accurate foot placement is important for dynamic balance during activities of daily living. Disruption of sensory information and prosthetic componentry characteristics may result in increased locomotor task difficulty for individuals with lower limb amputation. This study investigated the accuracy and precision of prosthetic and intact foot placement during a targeted stepping task in individuals with unilateral transtibial amputation (IUTAs; N = 8, 47 ± 13 yrs), compared to the preferred foot of control participant's (N = 8, 33 ± 15 yrs). Participants walked along a 10-metre walkway, placing their foot into a rectangular floor-based target with dimensions normalised to a percentage of participant's foot length and width; 'standard' = 150% x 150%, 'wide' = 150% x 200%, 'long' = 200% x 150%. Foot placement accuracy (relative distance between foot and target centre), precision (between-trial variability), and foot-reach kinematics were determined for each limb and target, using three-dimensional motion capture. A significant foot-by-target interaction revealed less mediolateral foot placement accuracy for IUTAs in the wide target, which was significantly less accurate for the intact (28 ± 12 mm) compared to prosthetic foot (16 ± 14 mm). Intact peak foot velocity (4.6 ± 0.8 m.s^-1) was greater than the prosthetic foot (4.5 ± 0.8 m.s^-1) for all targets. Controls were more accurate and precise than IUTAs, regardless of target size. Less accurate and precise intact foot placement in IUTAs, coupled with a faster moving intact limb, is likely due to several factors including reduced proprioceptive feedback and active control during prosthetic limb single stance. This could affect activities of daily living where foot placement is critical, such as negotiating cluttered travel paths or obstacles whilst maintaining balance.

Optimal lighting levels for stair safety: Influence of lightbulb type and brightness on confidence, dynamic balance and stepping characteristics

INTRODUCTION

Poor lighting has been associated with stair falls in young and older adults. However, current guidelines for illuminating stairs seem arbitrary, differ widely between sources, and are often difficult to interpret.

AIMS

Here we examined the influence of real-world bulb illumination properties on stair descent safety in young and older adults, with a view to generating preliminary evidence for appropriate lightbulb use/stair illumination.

METHODS

Stair tread illumination (lx) was measured in a standard UK home (2.23 m ceiling) from a low (50 W; 630 lm) and a high (103 W, 1450 lm) power compact fluorescent lamp (CFL) bulb from the time they were turned on until they reached full brightness. This enabled modelling of their illumination characteristics during warm up. Illumination was also measured from a low (40 W, 470 lm) and a high (100 W, 1521 lm) power LED bulb at first turn-on. Computer-controlled custom lighting then replicated these profiles, in addition to a Bright control (350 lx), on an instrumented staircase descended (3 × trials per light condition) by 12 young (25.3 ± 4.4 years; 5 males), 12 higher ability older (HAOA: 69.6 ± 4.7 years; 5 males) and 13 lower ability older (LAOA: 72.4 ± 4.2; 3 males) healthy adults. Older adults were allocated to ability groups based on physiological and cognitive function. Stair-specific confidence was assessed prior to the first descent in each new lighting condition, and whole-body 3D kinematics (Vicon) quantified margins of stability and foot clearances with respect to the step edges. Mixed ANOVAs examined these measures for within-subject effects of lighting (×5), between-subject effects of age (×3) and interactions between lighting and age.

RESULTS

Use of CFL bulbs led to lower self-reported confidence in older adults (20.37%, p = .01), and increased margins of stability (12.47%, p = .015) and foot clearances with respect to the step edges (10.36%, p = .003). Importantly, using CFL bulbs increased foot clearance variability with respect to the bottom step (32.74%, p = .046), which is where a high proportion of falls occur.

CONCLUSION

Stair-tread illumination from CFL bulbs at first turn on leads to less safe stair negotiation. We suggest high powered LED bulbs may offer a safer alternative.

Centre of mass control is reduced in older people when descending stairs at an increased riser height

BACKGROUND

Maintaining body centre of mass (CoM) lowering velocity within manageable/safe limits during stair descent can be problematic for older individuals due to reduced ranges of motion at the involved joints (ankle and knee) and a reduced ability to generate adequate joint moments at the extremes in joint ranges of motion. These problems are likely to magnify in circumstances where the distance of lowering increases, or when misjudging the height of lowering.

RESEARCH QUESTION

How does a 50% increase in standard stair riser-height affect control of CoM velocity and acceleration of older people during stair descent?

METHODS

Fifteen older (75 ± 3 years) and seventeen young (25 ± 4 years) healthy adults descended a 4-step staircase, at two riser-heights: 170 mm, 255 mm. Changes in peak vertical CoM acceleration and velocity, and lower-limb joint kinetics (moments, work) during landing and lowering phases of stair descent were assessed using a mixed-design repeated measures analysis of variance.

RESULTS

Peak CoM accelerations and velocities during landing and lowering were lower in older compared to young adults and increased in both groups at 255 mm riser-height. Duration of lowering also increased, particularly for older adults. Peak ankle moments during landing and lowering, which were lower in older compared to young adults, increased when descending from 255 mm riser-height, whilst the peak knee moment reduced. Both groups produced increased landing-limb negative (eccentric) ankle joint work when descending from 255 mm, but increases were greater for older adults (87.8%) compared to young (76.1%).

SIGNIFICANCE

Descending stairs became more challenging in both age groups as riser-height increased. Older adults adopted a strategy of reducing CoM velocity to lessen the eccentric landing demands. In both groups, but more so older adults, there was a greater reliance on using leading-limb eccentric plantarflexion at 255 mm riser-height compared to 170 mm, to arrest/control increased downward CoM velocity and acceleration during landing.

Nanoscale mechanics of microgel particles

Microgel particles are highly tuneable materials that are useful for a wide range of industrial applications, such as drug delivery, sensing, nanoactuation, emulsion stabilisation and use as cell substrates. Microgels have also been used as model systems investigating physical phenomena such as crystallization, glass-formation, jamming, ageing and complex flow behaviour. The responsiveness of microgel systems such as poly(N-isopropylacrylamide) (PNIPAm) to external stimuli has been established in fundamental investigations and in applications and recent work has begun to quantify the mechanics of individual particles. However little focus has been placed on determining their internal mechanical properties, which is likely to relate to their nonuniform internal structure. In this work we combine atomic force microscopy, force spectroscopy and dynamic light scattering to mechanically profile the internal structure of microgel particles in the size range of ∼100 nm, which is commonly used both in practical applications and in fundamental studies. Nanoindentation using thermally stable cantilevers allows us to determine the particle moduli and the deformation profiles during particle compression with increasing force, while peak force nanomechanical mapping (PF-QNM) AFM is used to capture high resolution images of the particles' mechanical response. Combining these approaches with dynamic light scattering allows a quantitative profile of the particles' internal elastic response to be determined. Our results provide clear evidence for a radial distribution in particle mechanical response with a softer outer "corona" and a stiffer particle core. We determine the particle moduli in the core and corona, using different force microscopy approaches, and find them to vary systematically both in the core (∼17-50 kPa) and at the outer periphery of the particles (∼3-40 kPa). Importantly, we find that highly crosslinked particles have equivalent moduli across their radial profile, reflecting their significantly lower radial heterogeneity. This ability to accurately and precisely probe microgel radial profiles has clear implications both for fundamental science and for industrial applications.

The addition of stripes (a version of the 'horizontal-vertical illusion') increases foot clearance when crossing low-height obstacles

Trips over obstacles are one of the main causes of falling in older adults, with vision playing an important role in successful obstacle negotiation. We determined whether a horizontal-vertical illusion, superimposed onto low-height obstacles to create a perceived increase in obstacle height, increased foot clearances during obstacle negotiation thus reducing the likelihood of tripping. Eleven adults (mean ± 1 SD: age 27.3 ± 5.1 years) negotiated obstacles of varying heights (3, 5, 7 cm) with four different appearance conditions; two were obstacles with a horizontal-vertical illusion (vertical stripes of different thickness) superimposed on the front, one was a plain obstacle and the fourth a plain obstacle with a horizontal black line painted on the top edge. Foot clearance parameters were compared across conditions. Both illusions led to a significant increase in foot clearance when crossing the obstacle, compared to the plain condition, irrespective of obstacle height. Superimposing a horizontal-vertical illusion onto low-height obstacles can increase foot clearance, and its use on the floor section of a double-glazing door frame for example may reduce the incidence of tripping in the home. Practitioner Summary: Low-height obstacles such as the floor section of a double-glazing door frame are potential tripping hazards. In a gait lab-based study we found that a horizontal-vertical illusion superimposed onto low-height obstacles led to significantly higher foot clearances; indicating their potential as a useful safety measure.

A nuclear magnetic resonance study of water in aggrecan solutions

Aggrecan, a highly charged macromolecule found in articular cartilage, was investigated in aqueous salt solutions with proton nuclear magnetic resonance. The longitudinal and transverse relaxation rates were determined at two different field strengths, 9.4 T and 0.5 T, for a range of temperatures and aggrecan concentrations. The diffusion coefficients of the water molecules were also measured as a function of temperature and aggrecan concentration, using a pulsed field gradient technique at 9.4 T. Assuming an Arrhenius relationship, the activation energies for the various relaxation processes and the translational motion of the water molecules were determined from temperature dependencies as a function of aggrecan concentration in the range 0-5.3% w/w. The longitudinal relaxation rate and inverse diffusion coefficient were approximately equally dependent on concentration and only increased by upto 20% from that of the salt solution. The transverse relaxation rate at high field demonstrated greatest concentration dependence, changing by an order of magnitude across the concentration range examined. We attribute this primarily to chemical exchange. Activation energies appeared to be approximately independent of aggrecan concentration, except for that of the low-field transverse relaxation rate, which decreased with concentration.

ESI-IMS-MS: A method for rapid analysis of protein aggregation and its inhibition by small molecules

Electrospray ionisation-ion mobility spectrometry-mass spectrometry (ESI-IMS-MS) is a powerful method for the study of conformational changes in protein complexes, including oligomeric species populated during protein self-aggregation into amyloid fibrils. Information on the mass, stability, cross-sectional area and ligand binding capability of each transiently populated intermediate, present in the heterogeneous mixture of assembling species, can be determined individually in a single experiment in real-time. Determining the structural characterisation of oligomeric species and alterations in self-assembly pathways observed in the presence of small molecule inhibitors is of great importance, given the urgent demand for effective therapeutics. Recent studies have demonstrated the capability of ESI-IMS-MS to identify small molecule modulators of amyloid assembly and to determine the mechanism by which they interact (positive, negative, non-specific binding, or colloidal) in a high-throughput format. Here, we demonstrate these advances using self-assembly of Aβ40 as an example, and reveal two new inhibitors of Aβ40 fibrillation.

An in vivo platform for identifying inhibitors of protein aggregation

Protein aggregation underlies an array of human diseases, yet only one small-molecule therapeutic targeting this process has been successfully developed to date. Here, we introduce an in vivo system, based on a β-lactamase tripartite fusion construct, that is capable of identifying aggregation-prone sequences in the periplasm of Escherichia coli and inhibitors that prevent their aberrant self-assembly. We demonstrate the power of the system using a range of proteins, from small unstructured peptides (islet amyloid polypeptide and amyloid β) to larger, folded immunoglobulin domains. Configured in a 48-well format, the split β-lactamase sensor readily differentiates between aggregation-prone and soluble sequences. Performing the assay in the presence of 109 compounds enabled a rank ordering of inhibition and revealed a new inhibitor of islet amyloid polypeptide aggregation. This platform can be applied to both amyloidogenic and other aggregation-prone systems, independent of sequence or size, and can identify small molecules or other factors able to ameliorate or inhibit protein aggregation.

Analysis of lower limb movement to determine the effect of manipulating the appearance of stairs to improve safety: a linked series of laboratory-based, repeated measures studies

Background

Falls on stairs are a common and dangerous problem for older people. This series of studies evaluated whether or not selected changes to the appearance of stairs could make them safer for older people to negotiate.

Objectives

To determine the effect of (1) a step edge highlighter and its position and (2) an optimised horizontal–vertical (H–V) visual illusion placed on a step riser on gait safety during stair descent and ascent.

Design

A series of studies using a repeated measures, laboratory-based design, investigating gait control and safety in independently mobile older people.

Setting

The University of Bradford Vision and Mobility Laboratory.

Participants

Fit and healthy older people aged 60 years of age or more, independently mobile, reasonably active and with normal healthy eyes and corrected vision.

Interventions

A step edge highlighter in a variety of offsets from the stair edge and an optimised H–V visual illusion placed on the stair riser. The H–V illusion was provided on a staircase by horizontal step edge highlighters on the tread edges and vertical stripes on the step risers.

Main outcome measures

Gait parameters that are important for safe stepping in ascent and descent, particularly toe clearance during stair ascent and heel clearance during stair descent.

Results

The step edge highlighter increased the precision of heel clearance during stepping and its positioning relative to the tread edge determined the extent of heel clearance over the tread edge. Positioning the highlighter away from the tread edge, as is not uncommonly provided by friction strips, decreased heel clearance significantly and led to greater heel scuffs. Although psychophysics experiments suggested that higher spatial frequencies of the H–V illusion might provide greater toe clearance on stair ascent, gait trials showed similar increased toe clearances for all spatial frequencies. When a 12 cycle per step spatial frequency H–V illusion was used, toe clearance increases of approximately 1 cm (17.5%) occurred without any accompanying changes in other important gait parameters or stability measures.

Conclusions

High-contrast tread edge highlighters present on steps and stairs and positioned flush with the edge of the tread or as near to this as possible should improve stair descent safety in older people. A H–V illusion positioned on the riser of a raised surface/walkway (e.g. kerbs) and/or the top and/or bottom of a stairway is likely to increase foot clearance over the associated step/stair edge, and appears not to lead to any decrement in postural stability. Thus, their use is likely to reduce trip risk and hence improve stair ascent safety. The effect of the step and stair modifications should be assessed in older people with visual impairment. The only other remaining assessment that could be made would be to assess fall prevalence on steps and stairs, perhaps in public buildings, with and without these modifications.

Funding

The National Institute for Health Research Public Health Research programme.

Acute paraumbilical vein recanalization: an unusual complication of acute pancreatitis

Acute pancreatitis is associated with a number of well-known complications and imaging findings. Spontaneous recanalization of the paraumbilical veins as a consequence of pancreatitis in a patient with an otherwise normal liver is, however, a rare entity. This case report depicts this unusual complication as a consequence of gallstone pancreatitis in a patient with a non-cirrhotic liver and no clinical or radiological evidence of portal hypertension. There was recanalization of the paraumbilical veins followed by thrombosis, which is believed to have propagated in a retrograde fashion into distal branches of the otherwise patent portal vein. A literature search for similar cases such as this has yielded no results. Although rare, clinicians and radiologists alike need to be aware of this finding. This case discussion highlights the embryology and anatomy of the paraumbilical veins, as well as discusses the management of paraumbilical and portal vein thrombosis.

Screening and classifying small-molecule inhibitors of amyloid formation using ion mobility spectrometry-mass spectrometry

The search for therapeutic agents which bind specifically to precursor protein conformations and inhibit amyloid assembly is an important challenge. Identifying such inhibitors is difficult since many protein precursors of aggregation are partially folded or intrinsically disordered, ruling out structure-based design. Furthermore, inhibitors can act by a variety of mechanisms, including specific or non-specific binding, as well as colloidal inhibition. Here we report a high throughput method based on ion mobility spectrometry-mass spectrometry (IMS-MS) that is capable of rapidly detecting small molecules that bind to amyloid precursors, identifying the interacting protein species, and defining the mode of inhibition. Using this method we have classified a variety of small molecules that are potential inhibitors of human islet amyloid polypeptide (hIAPP) aggregation or amyloid-beta 1-40 (Aβ40) aggregation as either specific, non-specific, colloidal or non-interacting. We also demonstrate the ability of IMS-MS to screen for inhibitory small molecules in a 96-well plate format and use this to discover a new inhibitor of hIAPP amyloid assembly.

Safety on stairs: influence of a tread edge highlighter and its position

BACKGROUND

Falls sustained when descending stairs are the leading cause of accidental death in older adults. Highly visible edge highlighters/friction strips (often set back from the tread edge) are sometimes used to improve stair safety, but there is no evidence for the usefulness of either.

OBJECTIVE

To determine whether an edge highlighter and its location relative to the tread edge affect foot placement/clearance and accidental foot contacts when descending stairs.

METHOD

Sixteen older adults (mean±1SD age; 71±7years) with normal vision (experiment 1) and eight young adults (mean±1SD age; 24±4years) with visual impairment due to simulated age-related cataract (experiment 2) completed step descent trials during which a high contrast edge highlighter was either not present, placed flush with the tread edge, or set back from the edge by 10mm or 30mm. Foot placement/clearance and the number of accidental foot contacts were compared across conditions.

RESULTS

In experiment 1, a highlighter set back by 30mm led to a reduction in final foot placement (p<0.001) and foot clearance (p<0.001) compared to a highlighter placed flush with the tread edge, and the percentage of foot clearances that were less than 5mm increased from 2% (abutting) to 17% (away30). In experiment 2, a highlighter placed flush with the tread edge led to a decrease in within-subject variability in final foot placement (p=0.004) and horizontal foot clearance (p=0.022), a decrease in descent duration (p=0.009), and a decrease in the number of low clearances (<5mm, from 8% to 0%) and the number of accidental foot contacts (15% to 3%) when compared to a tread edge with no highlighter present.

CONCLUSIONS

Changes to foot clearance parameters as a result of highlighter presence and position suggest that stairs with high-contrast edge highlighters positioned flush with the tread edge will improve safety on stairs, particularly for those with age-related visual impairment.

Quantitative parametric MRI of articular cartilage: a review of progress and open challenges

With increasing life expectancies and the desire to maintain active lifestyles well into old age, the impact of the debilitating disease osteoarthritis (OA) and its burden on healthcare services is mounting. Emerging regenerative therapies could deliver significant advances in the effective treatment of OA but rely upon the ability to identify the initial signs of tissue damage and will also benefit from quantitative assessment of tissue repair in vivo. Continued development in the field of quantitative MRI in recent years has seen the emergence of techniques able to probe the earliest biochemical changes linked with the onset of OA. Quantitative MRI measurements including T(1), T(2) and T(1ρ) relaxometry, diffusion weighted imaging and magnetisation transfer have been studied and linked to the macromolecular structure of cartilage. Delayed gadolinium-enhanced MRI of cartilage, sodium MRI and glycosaminoglycan chemical exchange saturation transfer techniques are sensitive to depletion of cartilage glycosaminoglycans and may allow detection of the earliest stages of OA. We review these current and emerging techniques for the diagnosis of early OA, evaluate the progress that has been made towards their implementation in the clinic and identify future challenges in the field.

The effects of virtual reality game training on trunk to pelvis coupling in a child with cerebral palsy

Background

Good control of trunk and pelvic movements is necessary for well controlled leg movements required to perform activities of daily living. The nature of movement coupling between the trunk and pelvis varies and depends on the type of activity. Children with cerebral palsy often have reduced ability to modulate coupling between the trunk and pelvis but movement patterns of the pelvis can be improved by training. The aim of this study was to examine how pelvis to trunk coupling changed while playing a computer game driven by pelvic rotations.

Methods

One boy with cerebral palsy diplegia played the Goblin Post Office game on the CAREN virtual rehabilitation system for six weeks. He navigated a flying dragon in a virtual cave towards randomly appearing targets by rotating the pelvis around a vertical axis. Motion of the pelvis and trunk was captured in real-time by a Vicon 612 optoelectronic system tracking two clusters of three markers attached to the sacrum and thoracic spine.

Results

Convex hull areas calculated from angle-angle plots of pelvic and trunk rotations showed that coupling increased over game training (F_1,11 = 7.482, p = 0.019). Reaching to targets far from the midline required tighter coupling than reaching near targets (F_1,12 = 10.619, p = 0.007).

Conclusions

Increasing coupling appears to be an initial compensation mechanism using the better controlled trunk to drive rotation of the pelvis. Co-contractions causing increased coupling are expected to reduce over longer exposure to training. The control scheme of the training game can be set to facilitate de-coupling of pelvic movements from the trunk. Using large ranges of pelvic rotation required more coupling suggesting that training of selective pelvic movements is likely to be more effective close to a neutral pelvic posture.

Seasonal and annual changes in soil respiration in relation to soil temperature, water potential and trenching

Soil respiration (rs), soil temperature (Ts) and volumetric soil water content were measured in a balsam fir (Abies balsamea (L.) Mill.) ecosystem from 1998 to 2001. Seasonal variation in root and microbial respiration, and covariation in abiotic factors confounded interpretation of the effects of Ts and soil water potential (Psis) on rs. To minimize the confounding effect of temperature, we analyzed the effect of Psis on rs during the summers of 1998-2000 when changes in Ts were slight. Soil respiration declined 25-50% in response to modest water stress (minimum Psis of -0.6 to -0.2 MPa), and between years, there was substantial variation in the relationship between rs and Psis. In the summer of 2000, 2-m2 plots were subjected to drought for 1 month and other plots were irrigated. The relationship between summertime rs and Psis in the experimental plots was similar to that estimated from the survey data obtained during the same summer. In late spring and early autumn of 2001, 2-m2 trenched and untrenched plots were subjected to drought or exposed to rainfall. It was dry in the early autumn and there was severe soil drying (Psis of -10 MPa in untrenched plots and -2 MPa in trenched plots). In spring, rs in untrenched plots responded more to modest water stress than rs in trenched plots, indicating that root respiration is more sensitive than microbial respiration to water stress at this time of year. The response to abiotic factors differed significantly between spring and autumn in untrenched plots but not in trenched plots, indicating that root activity was greater in early autumn than in late spring, and that roots acclimated to the sustained, severe water stress experienced before and during the autumn.

The anisotropic hydraulic permeability of human lumbar anulus fibrosus. Influence of age, degeneration, direction, and water content

STUDY DESIGN

Experimental investigation to determine the effect of intervertebral disc degeneration on the kinetic behavior of fluid in human anulus fibrosus.

OBJECTIVES

To measure the hydraulic permeability coefficient of anulus fibrosus specimens in the axial, circumferential, and radial directions to determine the anisotropic permeability behavior of nondegenerate and degenerate human intervertebral discs over a range of ages.

SUMMARY OF BACKGROUND DATA

Fluid, a major component of normal intervertebral discs, plays a significant role in their load-supporting mechanisms. Transport of fluid through the intervertebral disc is important for cell nutrition and disc viscoelastic and swelling behaviors. The hydraulic permeability coefficient is the most important material property governing the rate of fluid transport. However, little is known about the anisotropic behavior of this kinetic property and how it is influenced by disc degeneration.

METHODS

Using a permeation testing apparatus developed recently, testing was performed on 306 axial, circumferential, and radial anulus fibrosus specimens from the posterolateral region of 30 human lumbar (L2-L3) discs. A new method, flow-controlled testing protocol, was developed to measure the hydraulic permeability coefficient.

RESULTS

The hydraulic permeability coefficient of anulus fibrosus depended significantly on the disc degenerative grade (P = 0.0001) and flow direction (P = 0.0001). For the nondegenerate group (Grade I), the hydraulic permeability was significantly anisotropic (P < 0.05), with the greatest value in the radial direction (1.924 x 10(-15) m4/Ns) and the lowest value in the circumferential direction (1.147 x 10(-15) m4/Ns). This anisotropic kinetic (flow) behavior of anulus fibrosus varied with disc degeneration. For the Grade III specimen group, there was no significant difference in hydraulic permeability coefficient among the three major directions (P = 0.37). With disc degeneration, the hydraulic permeability coefficient was decreased in the radial direction and increased in the axial and circumferential directions. The variations of hydraulic permeability coefficient from nondegenerate discs (Grade I) to mildly degenerate discs (Grade II) in each direction were significant (P < 0.05). However, the changes in permeability from Grade II to Grade III groups were not significant (P > 0.05) except in the circumferential direction (3.8% increase; P < 0.05).

CONCLUSIONS

The hydraulic permeability of human nondegenerate anulus fibrosus is direction-dependent (i.e., anisotropic), with the greatest permeability in the radial direction. With disc degeneration, the radial permeability of anulus fibrosus decreases, mainly because of decreased water content, and the axial and circumferential permeability coefficients increase, mainly because of structural change, leading to more isotropic permeability behavior for Grade III discs.

Streaming potential of human lumbar anulus fibrosus is anisotropic and affected by disc degeneration

The streaming potential responses of non-degenerate and degenerate human anulus fibrosus were measured in a one-dimensional permeation configuration under static and dynamic loading conditions. The goal of this study was to investigate the influence of the changes in tissue structure and composition on the electrokinetic behavior of intervertebral disc tissues. It was found that the static streaming potential of the anulus fibrosus depended on the degenerative grade of the discs (p = 0.0001) and on the specimen orientation in which the fluid flows (p = 0.0001). For a statically applied pressure of 0.07 MPa, the ratio of streaming potential to applied pressure ranged from 5.3 to 6.9 mV/MPa and was largest for Grade I tissue with axial orientation and lowest for Grade III tissue with circumferential orientation. The dynamic streaming potential responses of anulus fibrosus were sensitive to the degeneration of the disc: the total harmonic distortion factor increased by 108%, from 3.92 +/- 0.66% (mean +/- SD) for Grade I specimens to 8.15 +/- 3.05% for Grades II and III specimens. The alteration of streaming potential reflects the changes in tissue composition and structure with degeneration. To our knowledge, this is the first reported data for the streaming potential of human intervertebral disc tissues. Knowledge of the streaming potential response of the intervertebral disc provides an understanding of potentially important signal transduction mechanisms in the disc and of the etiology of intervertebral disc degeneration.

Shear mechanical properties of human lumbar annulus fibrosus

Function, failure, and remodeling of the intervertebral disc are all related to the stress and strain fields in the tissue and may be calculated by finite element models with accurate material properties, realistic geometry, and appropriate boundary conditions. There is no comprehensive study in the literature investigating the shear material properties of the annulus fibrosus. This study obtained shear material properties of the annulus fibrosus and tested the hypothesis that these properties are affected by the amplitude and frequency of shearing, applied compressive stress, and degenerative state of the tissue. Cylindrical specimens with an axial orientation from seven nondegenerated and six degenerated discs were tested in torsional shear under dynamic and static conditions. Frequency sweep experiments over a physiological range of frequencies (0.1-100 rad/sec) at a shear strain amplitude of 0.05 rad were performed under three different axial compressive stresses (17.5, 25, and 35 kPa). At the largest compressive stress, shear strain sweep experiments (strain amplitude range: 0.005-0.15 rad at a frequency of 5 rad/sec) and transient stress-relaxation tests (shear strain range: 0.02-0.15 rad) were performed. The annulus fibrosus material was less stiff and more dissipative at larger shear strain amplitudes, stiffer at higher frequencies of oscillation, and stiffer and less dissipative at larger axial compressive stresses. The dynamic shear modulus, /G*/, had values ranging from 100 to 400 kPa, depending on the experimental condition and degenerative level. The shear behavior was also predominantly elastic, with values for the tangent of the phase angle (tandelta) ranging from 0.1 to 0.7. The annulus material also became stiffer and more dissipative with degenerative grade; however, this was not statistically significant. The results indicated that nonlinearities, compression/shear coupling, intrinsic viscoelasticity, and, to a lesser degree, degeneration all affect the shear material behavior of the annulus fibrosus, with important implications for load-carriage mechanisms in the intervertebral disc. These material complexities should be considered when choosing material constants for finite element models.

Composition and dynamics of articular cartilage: structure, function, and maintaining healthy state

Disorders of articular cartilage represent some of the most common and debilitating diseases encountered in orthopaedic practice. Understanding the normal functioning of articular cartilage is a prerequisite to understanding its pathologic processes. The mechanical properties of articular cartilage arise from the complex structure and interactions of its biochemical constituents: mostly water, electrolytes, and a solid matrix composed primarily of collagen and proteoglycan. The viscoelastic properties of cartilage, due primarily to fluid flow through the solid matrix, can explain much of the deformational responses observed under many loading conditions. Degenerative processes can often be explained by a breakdown of the normal load-bearing capacity of cartilage which arises from the mechanics of this fluid flow. Several factors which may lead to such a breakdown include direct trauma to the cartilage, obesity, immobilization, and excessive repetitive loading of the cartilage. Sports activity, without traumatic injury, does not appear to be a risk factor for the development of osteoarthritis in the normal joint; however, such activity may be harmful to an abnormal joint.

Degeneration affects the anisotropic and nonlinear behaviors of human anulus fibrosus in compression

Axial and radial specimens of non-degenerate and degenerate human anulus fibrosus (AF) were tested in confined compression to test the hypothesis that degeneration significantly affects the compressive properties of AF. Due to the highly oriented structure of AF, a secondary objective was to investigate anisotropic behaviors of AF in compression. Uniaxial swelling and stress relaxation experiments were performed on site-matched samples of anulus from the anterior outer region of L2-3 intervertebral discs. The experimental stress-relaxation behavior was modeled using the finite deformation biphasic theory and a finite-difference approximation scheme. Significant effects of degeneration but not orientation were detected for the reference stress offset, sigma(offset), and parameters describing the compressive stiffness (i.e. reference aggregate modulus, H(A0), and nonlinear stiffening coefficient, beta). Average values were 0.13+/-0.06 and 0.05+/-0.05 MPa for sigma(offset), 0.56+/-0.21 and 1.10+/-0.53 MPa for H(A0) and 2.13+/-1.48 and 0.44+/-0.61 for beta for all normal and degenerate specimens, respectively. No significant effect of degeneration or orientation were detected for either of the parameters describing the strain-dependent permeability (i.e. reference permeability, k0 and strain-dependent permeability coefficient, M) with average values for all specimens of 0.20+/-0.10 x 10(-15) m4/N-s and 1.18+/-1.30 for k0 and M, respectively. The loss of sigma(offset) was compensated with an elastic stiffening and change in the shape of the equilibrium stress-strain curve with H(A0) for degenerate tissues almost twice that of normal tissues and beta less than one sixth. The increase in reference elastic modulus with degeneration is likely related to an increase in tissue density resulting from the loss of water content. The significant effects of degeneration reported in this study suggested a shift in load carriage from fluid pressurization and swelling pressure to deformation of the solid matrix of the AF. The results also suggest that the highly organized and layered network of the anulus fibrosus, which gives rise to significant anisotropic effects in tension, does not play a major role in contributing to the magnitude of compressive stiffness or the mechanisms of fluid flow of the anulus in the confined compression configuration.

Stabilization of ulnar carpometacarpal dislocations or fracture dislocations

For the management of ulnar carpometacarpal dislocations or fracture dislocations, various authors have suggested closed reduction and percutaneous pin fixation, or open reduction and internal fixation with the use of transversely oriented pins. The methods can be problematic with failure of fixation or injury to tendons or nerves. A stable internal fixation alternative uses intramedullary metacarpal Steinmann pins or Kirschner wires, passed across the carpometacarpal joint into the hamate. If the fixation devices exit through the triquetrum and the lunate, then the finger metacarpal phalangeal joints may be left with full active motion. This method has provided ease of placement, stability, and no loss of fixation in 9 cases. An associated coronal fracture of the hamate may be fixed with small Kirschner wires or with a small lag screw, which can be placed through the same incision.

Tensile properties of nondegenerate human lumbar anulus fibrosus

STUDY DESIGN

The in vitro tensile behavior of multiple-layer samples of anulus fibrosus were investigated from nondegenerate intervertebral discs.

OBJECTIVES

To quantify the intrinsic tensile behavior of nondegenerate anulus fibrosus and the variations with position and age in the intervertebral disc.

SUMMARY OF BACKGROUND DATA

Tension is an important loading mode in the anulus fibrosus. The tensile behavior of single- and multiple-layer samples of anulus fibrosus has been shown to vary with specimen orientation, position in the disc, and environmental conditions. Little is known of the changes in these site-specific tensile properties of the anulus with aging or degeneration of the intervertebral disc.

METHODS

Multiple-layer specimens of anulus fibrosus were harvested with an orientation parallel to the circumference of the disc. Constant strain rate and uniaxial tensile tests were performed in 0.15 mol/l NaCl at slow strain rates to measure the intrinsic properties of the collagen-proteoglycan matrix of the anulus fibrosus. The tensile modulus, failure stress, failure strain, and strain energy density were determined. Statistical analyses were done to evaluate regional and age-related differences in these properties.

RESULTS

Significant radial and circumferential variations in the intrinsic tensile properties of anular samples were detected. The anterior anulus fibrosus had larger values for tensile moduli and failure stresses than the posterolateral anulus. Also, the outer regions of the anulus had greater moduli and failure stresses and lower failure strains than the inner regions. Strain energy density did not vary significantly with region. Significant, but very weak, correlations were detected between tensile properties and age of the intervertebral disc.

CONCLUSIONS

The observed variations in tensile behavior of multiple-layer anulus samples indicate that larger variations in tensile modulus and failure properties occur with radial position in the disc than from anterior to posterolateral regions. This pattern is likely related to site-specific variations in the tensile properties of the single-layer samples of anulus fibrosus lamellae and the organization of successive lamellae and their interactions. The results of the present study suggest that factors other than age, such as compositional and structural variations in the disc, are the most important determinants of tensile behavior of the anulus fibrosus.

Degeneration and aging affect the tensile behavior of human lumbar anulus fibrosus

STUDY DESIGN

Samples of human lumbar (L3-L4) anulus fibrosus from four different anatomic sites (anterior outer, posterolateral inner), ranging from normal to severely degenerate, were studied in uniaxial tension and measured for water content.

OBJECTIVES

To evaluate the effects of aging and degeneration on the tensile properties and hydration of the anulus fibrosus in a site-specific manner. The relationship between hydration and parameters of the tensile behavior were investigated.

SUMMARY OF BACKGROUND DATA

Degeneration and aging have been shown to be related to dramatic changes in the composition and structure of the anulus fibrosus. The associated changes in the tensile, compressive, and shear properties of the anulus fibrosus have not been documented. Numerical studies using finite element models have attempted to simulate the degenerative process by incorporating estimated mechanical properties meant to represent the degenerate anulus fibrosus. Their results present findings that suggest that altered material properties of the anulus fibrosus affect the mechanics of the entire intervertebral disc.

METHODS

Samples of human lumbar anulus fibrosus were classified by grade of degeneration based on a morphologic grading scheme. Multiple layer anulus specimens from four sites in the disc were tested in uniaxial tension under quasistatic conditions in a physiologic saline bath. The tensile modules, Poisson's ratio, failure stress and strain, the strain energy density to failure, and the corresponding hydration were determined for each sample.

RESULTS

The Poisson's ratio, failure stress, and strain energy density of the anulus fibrosus were found to be affected significantly by degeneration, with some evidence of a sensitivity of the tensile modulus to grade of degeneration. All material properties were found to exhibit a significant and greater dependence on site within the disc than on degenerative grade. Weak correlations between aging and the Poisson's ratio and strain energy density were observed. Water content of anulus fibrosus tissue was not affected by degeneration or aging, although correlations with tensile properties were observed.

CONCLUSIONS

The dramatic changes in morphology, composition, and structure that occur in anulus fibrosus with aging and degeneration are accompanied by specific variations in the tensile properties, which were generally small in magnitude. Position of the anulus fibrosus within the intervertebral disc, particularly in the radial direction, appeared to be the most important variable affecting anulus fibrosus tensile properties. This dependence on position did not change with either aging or degeneration. Results from the present study may be useful in future finite element models to assess how altered material properties of the anulus fibrosus during degeneration and aging may affect the mechanics of the entire intervertebral disc.

Use of commercial enzyme kits and fatty acid production for the identification of Serpulina hyodysenteriae: a potential misdiagnosis

The accuracy of identification of Serpulina hyodysenteriae strains grown in a complex medium was 90% when 2 commercial test kits were used. Unlike the other S. hyodysenteriae strains, S. hyodysenteriae strain P35/2 was unusual in being indole negative. The nonpathogenic intestinal spirochete PWS/A, which is from a different species, was indole positive and alpha-galactosidase negative. Identification of these spirochetes on the basis of these kits alone would have been incorrect. The analysis of volatile fatty acids by gas chromatography showed that the ratio of acetic to butyric acid was from 11:1 to 44:1 for S. hyodysenteriae strains, which distinguished them from the other spirochetes. The exception was PWS/A (acetic: butyric of 32:1), but this spirochete, unlike the S. hyodysenteriae spirochetes, also produced isobutyric acid. Short chain fatty acid (SCFA) analysis by high-performance liquid chromatography detected different SCFAs in addition to acetic and butyric acids. These additional SCFAs did not contribute to further differentiation of the porcine spirochetes.

Radial nerve palsy caused by open humeral shaft fractures

Although radial nerve palsy associated with a closed humeral shaft fracture may be managed by observation, it is our experience that an open humeral shaft fracture with radial nerve palsy requires exploration of the nerve. In a series of 14 patients with radial nerve palsy caused by an open humeral shaft fracture, 9 (64%) of the 14 patients had a radial nerve that was either lacerated or interposed between the fracture fragments. There was an equal incidence of radial nerve lacerations or entrapments in types I, II, and III open humeral shaft fractures. Epineural radial nerve repair, done primarily or secondarily, provided a satisfactory return of radial nerve function. Rigid fixation of the associated fracture is the recommended treatment.

Correlating magnetic resonance imaging with the biochemical content of the normal human intervertebral disc

Magnetic resonance imaging was used to determine the T2 relaxation times of prepared proteoglycan solutions and of normal human intervertebral disc tissue from the annulus fibrosus (AF) and nucleus pulposus (NP). The collagen, proteoglycan, and water contents of the disc tissue samples were determined by biochemical assays after they were scanned. Correlations among 1/T2, collagen, proteoglycan, and water contents of the tissue samples and among 1/T2, water, and proteoglycan contents of the proteoglycan solutions were calculated. A moderate negative correlation between 1/T2 and water content was noted for the tissue samples, and a very high negative correlation was found between 1/T2 and water content for the proteoglycan solutions. The very high positive correlation between 1/T2 and proteoglycan content of the proteoglycan solutions is probably due to this negative correlation between 1/T2 and water content. There was no significant correlation between 1/T2 and proteoglycan content of the tissues. The moderate positive correlation between 1/T2 and collagen content is probably due to the high negative correlation between collagen content and water content. No significant correlation was found between the collagen and proteoglycan contents of the tissues. Thus it appears that the data confirm previous reports in the literature that the collagen of the disc tissue functions to control its water content.

Concurrent oral surgery and orthopaedic treatment in the multiply injured patient: is there an increased incidence of orthopaedic sepsis?

Fifty-five patients requiring oral surgery and orthopaedic care were studied prospectively and compared to a control group. Six patients received no antibiotics and one developed an orthopaedic operative site infection due to a mouth organism. Seventeen patients had concurrent surgery and perioperative antibiotic usage and no infections occurred. Twenty-six patients required multiple operations and courses of antibiotic treatment and five developed infections. Enterobacter infections were common and emerge because they are resistant to first-generation cephalosporins. Treatment by a perioperative first-generation cephalosporin is recommended, followed by throat cultures and treatment by antibiotics specific for cultured organisms for patients requiring subsequent operations.

Treatment of Bennett, Rolando, and vertical intraarticular trapezial fractures

Intraarticular fractures at the first trapeziometacarpal joint include Bennett, Rolando, and vertical intraarticular fractures of the trapezium. If these fractures heal in a displaced position, a traumatic arthritis quickly develops at the thumb base. Open reduction and lag screw rigid internal fixation of a Bennett fracture is advisable if a satisfactory closed reduction cannot be obtained. If the palmar and dorsal displaced fragments of a Rolando fracture are of adequate size, an open reduction internal fixation may be performed with small lag screws incorporated through a T- or L-shaped buttress plate. A displaced vertical intraarticular fracture of the trapezium may be easily misdiagnosed as a trivial chip fracture, unless specific radiographic views are obtained. Open reduction internal fixation is the only treatment method that will provide a satisfactory outcome for this fracture.

Enzymatic hydrolysis of diethylpyrocarbonate, a commonly used histidine modifying agent, by esterases

Diethylpyrocarbonate, a reagent commonly used to modify active site histidines in enzymes, was found to be hydrolyzed by several esterases. Two of these, cutinase, a typical serine esterase from the fungus Fusarium solani pisi, and thioesterase B from the uropygial gland of the mallard duck Anus platyrhynchus, hydrolyzed diethylpyrocarbonate so rapidly that histidine modification could not be detected except when the enzymic activity was inhibited by diisopropylfluorophosphate treatment or by the presence of critical micellar concentrations of sodium dodecyl sulphate. Possible loss of diethylpyrocarbonate should be of concern when this reagent is used to test for available histidines in hydrolytic enzymes.

Immediate internal fixation of open fractures of the diaphysis of the forearm

Between 1975 and 1983, fifty-seven patients were treated at Sunnybrook and Harborview Medical Centers with immediate internal plate fixation of an open diaphyseal fracture of the forearm. Fifty patients were available for follow-up, which ranged from one to nine years and averaged three years. The injuries were classified on the basis of the extent of soft-tissue injury as defined by Gustilo and Anderson, and consisted of twenty Type-I injuries, nineteen Type-II injuries, and eleven Type-III injuries. The complications included deep infection in two patients and non-union in six. The functional results were excellent or good in 85 per cent of the series. This study demonstrates that immediate stable plate fixation is a beneficial method of treatment of open fractures of the forearm. The results are related to the severity of the initial soft-tissue injury and the surgical technique. Autogenous cancellous bone-grafting at the time of closure of the wound in comminuted fractures in which interfragmental compression cannot be obtained is recommended.