Medical Engineering & Physics - Articles in Press

Influence of the frequency of the external mechanical stimulus on bone healing: A computational study - Corrected Proof

L.A. González-Torres, M.J. Gómez-Benito, M. Doblaré, J.M. García-Aznar — 2010-03-08

Abstract: The mechanical environment considerably affects the evolution of the bone healing process. However, the effect of an external cyclic stimulation on the process has not yet been fully clarified. The aim of the present work is to evaluate the distribution of different mechanical variables in the fracture callus when an external cyclic stimulation is applied at different frequencies, in order to investigate those stimuli most likely to regulate bone healing. To perform this analysis an axisymmetric poroelastic finite element model of a sheep metatarsus fracture has been developed and several mechanical variables quantified within the callus: deviatoric strain, octahedral strain, pore pressure and fluid flow velocity. The applied mechanical stimulus corresponds to a compression displacement of 0.02mm at frequencies of 1, 50 and 100Hz. The fluid flow velocity experiences considerable variations in amplitude and peak value when the frequency of the external stimulus changes, while the rest of the mechanical variables are not significatively modified. We conclude that the change in the frequency of the external mechanical stimulus directly affects the interstitial fluid flow velocity in the fracture callus. This change in the fluid flow velocity may induce movement of wastes, feeds or growth factors, as well as stimulating cellular differentiation and proliferation by means of changes in the mechanical environment of the callus. In addition, the results of this work suggest that, to obtain a more significant effect of cyclic stimulation, higher frequencies with lower amplitude than those normally used in previous experimental works are needed.

Recovery of 0.1Hz microvascular skin blood flow in dysautonomic diabetic (type 2) neuropathy by using Frequency Rhythmic Electrical Modulation System (FREMS) - Corrected Proof

L. Bocchi, A. Evangelisti, M. Barrella, L. Scatizzi, M. Bevilacqua — 2010-03-08

Abstract: Synchronized oscillation of smooth muscle cells tension in arterioles is the main control system of microvascular skin blood flow. An important autogenic vasomotion activity is recognized in 0.1Hz oscillations through power spectrum analysis of laser Doppler flowmetry. Severe dysautonomia in diabetic neuropathy is correlated with loss of 0.1Hz vasomotor activity, hence with impaired blood microcirculation. FREMS is a novel transcutaneous electrotherapy characterized by sequences of electrical stimuli of high voltage and low pulse duration which vary both in frequency and duration. We have evaluated the changes in laser Doppler flow in the volar part of the forearm before, during and after FREMS. Normal controls (, 6 females, age range 21–39 years) demonstrated significant 0.1Hz vasomotion power spectra at baseline conditions associated with large oscillations of adrenergic cutaneous sweat activity sampled from the hand; people with diabetes type 2 and severe dysautonomia (, 5 females, age range 63–75 years) displayed a significant decrease of 0.1Hz vasomotion power spectra. During FREMS application we observed an increase () of 0.1Hz vasomotion power spectra only in the diabetic group, despite persistence of adrenergic cutaneous sweat activity suppression in this group. However, after the application of the stimuli, the relative energy values around the 0.1Hz peak remained significantly higher than preapplication values in the diabetic group (). From these findings, we suggest that FREMS is able to synchronize smooth cell activity, inducing and increasing 0.1Hz vasomotion, independently from the autonomic nervous system.

Influence of surgical treatment for disc degeneration disease at C5–C6 on changes in some biomechanical parameters of the cervical spine - Corrected Proof

Yuan Li, Gladius Lewis — 2010-03-08

Abstract: A detailed three-dimensional solid model of the full cervical spine (C1–C7 levels) and the finite element analysis method were used to investigate the extent of changes in various biomechanical properties brought about when surgical methods are used to treat condition(s) caused by or are a sequela of disc degeneration disease at the C5–C6 level. The surgical methods simulated were anterior cervical discectomy and fusion, with interbody fusion achieved using a notional brick-shaped graft only; anterior cervical discectomy alone; percutaneous nucleotomy; and three variants of nucleus replacement. The control case was a model of an intact, healthy, adult spine. Each of these seven models was subjected to (1) flexion moment, extension moment, left lateral bending moment, right lateral bending moment, clockwise-acting axial rotation moment, and counterclockwise-acting axial rotation moment, with a compression pre-load applied simultaneously with each of these loadings and (2) an axial compression force (applied as a uniform pressure) only. For each combination of model and applied loading, the maximum von Mises stress and the maximum strain energy density were determined for tissues at the treated level, at one level above the treated level, and at one level below the treated level and (2) the total principal rotation angles at each of the intersegmental positions of the entire model. In addition, for each of the study cases, we obtained the longitudinal displacement of each of the models when subjected to the axial compression force only.We found markedly fewer changes (relative to the results when the intact, healthy spine model was used) in each of the above-mentioned biomechanical parameters above a specified threshold in the case of the simulated percutaneous nucleotomy and simulated nucleus replacement models, on one hand, compared to the simulated fusion and simulated discectomy models, on the other. This finding is in consonance with the evolving clinical practice of using minimally invasive surgical methods for treating problem(s) such as soft cervical disc herniations.

Fabrication and characterization of nano-composite scaffold of PLLA/silane modified hydroxyapatite - Corrected Proof

Xuejun Wang, Guojun Song, Tao Lou — 2010-03-02

Abstract: In order to improve the interfacial connection of hydroxyapatite (HAP) to poly-l-lactic acid (PLLA), γ-methacryloxypropyl-trimethoxysilane (γ-MPS) was used as a coupling agent to modify the surface of nano-HAP (NHAP) particles. The FTIR and XPS results showed γ-MPS was successfully bonded on the surface of NHAP. Silane modified nano-HAP (MNHAP) and PLLA were fabricated to nano-composite scaffold by a thermally induced phase separation method. The characterization of the composite scaffold showed that the scaffold had a nano-fibrous PLLA network (fiber size 100–800nm), an interconnective microporous structure (1–8μm) and high porosity (>90%). MNHAP was homogeneously distributed in the scaffold, also partly set in the nano-PLLA fibers. As a result, the compressive modulus and the protein adsorption of PLLA/MNHAP (80:20, w/w) composite scaffold increased to 4.2-fold and 2.8-fold compared with those of a pure PLLA scaffold. Incorporating MNHAP into PLLA network also buffered the pH reduction and reduced the weight loss in vitro degradation significantly.

Enhanced bone structural analysis through pQCT image preprocessing - Corrected Proof

T. Cervinka, J. Hyttinen, H. Sievanen — 2010-03-02

Abstract: Several factors, including preprocessing of the image, can affect the reliability of pQCT-measured bone traits, such as cortical area and trabecular density. Using repeated scans of four different liquid phantoms and repeated in vivo scans of distal tibiae from 25 subjects, the performance of two novel preprocessing methods, based on the down-sampling of grayscale intensity histogram and the statistical approximation of image data, was compared to 3×3 and 5×5 median filtering. According to phantom measurements, the signal to noise ratio in the raw pQCT images (XCT 3000) was low (∼20dB) which posed a challenge for preprocessing. Concerning the cortical analysis, the reliability coefficient (R) was 67% for the raw image and increased to 94–97% after preprocessing without apparent preference for any method. Concerning the trabecular density, the R-values were already high (∼99%) in the raw images leaving virtually no room for improvement. However, some coarse structural patterns could be seen in the preprocessed images in contrast to a disperse distribution of density levels in the raw image. In conclusion, preprocessing cannot suppress the high noise level to the extent that the analysis of mean trabecular density is essentially improved, whereas preprocessing can enhance cortical bone analysis and also facilitate coarse structural analyses of the trabecular region.

Metrological characterization of a cycle-ergometer to optimize the cycling induced by functional electrical stimulation on patients with stroke - Corrected Proof

2010-02-22

Abstract: Functional electrical stimulation (FES) is a well established method in the rehabilitation of stroke patients. Indeed, a bilateral movement such as cycling induced by FES would be crucial for these patients who had an unilateral motor impairment and had to recover an equivalent use of limbs. The aim of this study was to develop a low-cost metrologically qualified cycle-ergometer, optimized for patients with stroke. A commercial ergometer was instrumented with resistive strain gauges and was able to provide the torque produced at the right and left crank, independently. The developed system was integrated with a stimulator, obtaining a novel FES cycling device able to control in real-time the movement unbalance. A dynamic calibration of the sensors was performed and a total torque uncertainty was computed. The system was tested on a healthy subject and on a stroke patient. Results demonstrated that the proposed sensors could be successfully used during FES cycling sessions where the maximum torque produced is about 9Nm, an order of magnitude less than the torque produced during voluntary cycling. This FES cycling system will assist in future investigations on stroke rehabilitation by means of FES and in new exercise regimes designed specifically for patients with unilateral impairments.

A pilot evaluation of a neuromuscular electrical stimulation (NMES) based methodology for the prevention of venous stasis during bed rest - Corrected Proof

2010-02-19

Abstract: Bed rest poses an increased risk factor for a potentially fatal venous thromboembolism (VTE). Lack of activation of the calf muscle pump during this resting period gives rise to venous stasis which may lead to deep vein thrombosis (DVT) development. Our aim was to investigate the effects that 4h of bed rest have on the lower limb hemodynamics of healthy subjects and to what extent electrically elicited contractions of the calf muscles can alleviate these effects. Outcome variables included popliteal vein blood flow and heart rate. Primary results indicated that the resting group experienced a significant decline in popliteal venous blood flow of ∼47% with ∼13% decrease in heart rate. The stimulated groups maintained a significantly higher venous blood flow and heart rate. Volume flow in the contralateral limb remained constant throughout the study and was comparable to that of the stimulated limb's recovery flow. The results suggest that even short periods of bed rest can significantly reduce lower limb blood flow which could have implications for DVT development. Electrically elicited calf muscle contractions significantly improve lower limb blood flow and can alleviate some debilitating effects of bed rest.

Development and testing of a perspiration measuring system - Corrected Proof

Yingjui Tsai, Chiachung Chen — 2010-02-19

Abstract: Sweating measurement is a very useful tool for the physiological health state of the human body. A sweating measuring system developed in this study was composed of several sensors. All sensors were calibrated to ensure the accuracy. Three pretreatment physiological states for test subjects before sweating measurement included sit and rest for 5min, walking for 5min, and running for 5min. The whole sweating value was measured and calculated over 5-min periods. The results of sweating measurement indicated the usefulness of this device. The sweating quantity of three states did not have a significant relationship with the height, weight and body mass index (BMI) values of subjects. The first sweating index is the difference between active treatment and sitting state. The second sweating index is the ratio between active state and sitting. The relationship between two sweating index and BMI values could be found. This device could serve as a detecting tool to establish the sweating database for normal conditions and to be used for diagnosis.

Inertial Gait Phase Detection for control of a drop foot stimulator: Inertial sensing for gait phase detection - Corrected Proof

D. Kotiadis, H.J. Hermens, P.H. Veltink — 2010-02-12

Abstract: An Inertial Gait Phase Detection system was developed to replace heel switches and footswitches currently being used for the triggering of drop foot stimulators. A series of four algorithms utilising accelerometers and gyroscopes individually and in combination were tested and initial results are shown. Sensors were positioned on the outside of the upper shank. Tests were performed on data gathered from a subject, sufferer of stroke, implanted with a drop foot stimulator and triggered with the current trigger, the heel switch. Data tested includes a variety of activities representing everyday life. Flat surface walking, rough terrain and carpet walking show 100% detection and the ability of the algorithms to ignore non-gait events such as weight shifts. Timing analysis is performed against the current triggering method, the heel switch. After evaluating the heel switch timing against a reference system, namely the Vicon 370 marker and force plates system. Initial results show a close correlation between the current trigger detection and the inertial sensor based triggering algorithms. Algorithms were tested for stairs up and stairs down. Best results are observed for algorithms using gyroscope data. Algorithms were designed using threshold techniques for lowest possible computational load and with least possible sensor components to minimize power requirements and to allow for potential future implantation of sensor system.

Re: Biomechanical study of mandible bone supporting a four-implant retained bridge finite element analysis of the influence of bone anisotropy and foodstuff position - Corrected Proof

Malik Hudieb, Shohei Kasugai — 2010-02-08

In this finite element study, Bonnet et al. investigated the biomechanical behavior of the All-on-four system. The FE model used indeed overcame several assumptions and simplifications incorporated in previous FE studies. However, in order to adopt and apply conclusions of numerical studies – including FE – to the clinical aspect, results should be interpreted considering the model simulation conditions; forces used and boundary fixation.

The effect of FES of the tibial nerve on physiological activation of leg muscles during gait - Corrected Proof

2010-02-08

Abstract: The effects of surface functional electrical stimulation (FES) of the tibial nerve of healthy subjects were evaluated. The FES was applied at three different times during gait: early, mid and late stances. The purpose of this work is to understand the effect of unilateral stimulation on the bilateral activation patterns of leg muscles, because FES is used in practice to improve gait, while associated neuromuscular change is not often measured. The experimental protocol presented here will be transferred to stroke subjects, who could benefit from improved push-off during gait. Results show that FES of the tibial nerve changes the offset timing of the tibialis anterior muscle on the stimulated side and the on- and offset timings of the tibialis anterior muscle of the leg contralateral to stimulation. Additionally, activity levels of the semitendinosus ipsilateral and tibialis anterior contralateral to the stimulated leg significantly decreased, with respect to the non-stimulated condition. For the semitendinosus, this was a difference of 6–7μV, with p<0.05. For the tibialis anterior, this was a difference of 7–15μV, with a significance of p=0.00, respectively.This information is important for future applications of stimulation as it means that stimulation not only affects the stimulated muscle but also the physiological motor control by the CNS.

Answer to the letter addressed to Editor concerning “Biomechanical study of mandible bone supporting a four-implant retained bridge. Finite element analysis of the influence of bone anisotropy and foodstuff position” - Corrected Proof

A.S. Bonnet, M. Postaire, P. Lipinski — 2010-02-03

We entirely agree with the reviewer's introductory remarks; to be clinically adopted our conclusions should be confirmed by additional studies, not only numerical. The author of the letter wrote that in our paper we “rose up several recommendations”. It is not true; our article contains only conclusions concerning our own investigations without any recommendation.

Effects of internal stress concentrations in plantar soft-tissue—A preliminary three-dimensional finite element analysis - Corrected Proof

Wen-Ming Chen, Taeyong Lee, Peter Vee-Sin Lee, Jin Woo Lee, Sung-Jae Lee — 2010-02-01

Abstract: It has been hypothesized that diabetic foot ulceration might be internally initiated. This study established a three-dimensional and nonlinear finite element model of a human foot complex with comprehensive skeletal and soft-tissue components. The model was validated by experimental data of subject-specific barefoot plantar pressure measurements. The feasibility of the model to predict the 3D, internal, plantar soft-tissue deformation and stress was evaluated. The preliminary results indicate that large von Mises stress occurs where plantar soft-tissue contacts with geometrically irregular bony structures, thus internal stress distribution within the plantar soft-tissue was dramatically influenced by bony prominences due to stress concentration. At the forefoot part, an average stress magnification factor of 3.01 was quantified. The lateral sesamoid bone associated to the 1st MTH showed the largest effect of stress concentration. The modeling approach presented provides a possible way to explore the complexity of the mechanical environment inside the plantar soft-tissue.

Swelling of medical grade silicones in liquids and calculation of their cross-link densities - Corrected Proof

Aziza Mahomed, David W.L. Hukins, Stephen N. Kukureka — 2010-01-18

Abstract: Four medical grade silicones were swollen, until they reached equilibrium (i.e. constant mass) in eight liquids at 25°C. The greatest swelling was obtained with n-heptane but the volume fraction, ϕ, of the silicones in their swollen state was not significantly different (p<0.05) in this liquid than in cyclohexane. For each grade of silicone, ϕ was plotted against δl, the liquid solubility parameter, for each liquid in which it was swollen. A second-order polynomial was plotted through the results; the minimum in this polynomial provided a value for the polymer solubility parameter, δp. The Flory polymer–liquid interaction parameter, χ, was calculated for the four best liquids, using Hildebrand's solubility parameter theory. An alternative method for calculating χ, directly from swelling measurements, was shown to produce physically unreasonable results. The cross-link density, υ, was calculated, from ϕ and χ, for each grade of silicone, using the Flory–Rehner equation. Since the values of two parameters involved in Hildebrand's theory cannot be determined reliably and because the Flory–Rehner equation is an approximation, absolute values of υ cannot be obtained. However, the relative values of υ obtained were higher for the harder grades then for the softer grades and similarly, the grades with the higher Young's modulus had higher υ values.

Development of tissue adhesion method using integrated low-level energies - Corrected Proof

2010-01-18

Abstract: We have developed a method that allows biological tissues to be adhered together with minimal invasion by delivering integrated low-level energies from heat, pressure, and vibration. Tensile tests on adhered slices of porcine aorta were performed to determine the relationships between adhesive strength and conditions such as adhesion temperature, time, pressure, and vibration. The maximal adhesive shear tensile strength using the proposed method was 0.2MPa, which is half the strength of the porcine aorta and stronger than surgical tissue adhesive. Adhesion strength increased in proportion to temperature, time, and pressure, and also in the presence of vibration, indicating that vibrational energy contributes to the adhesive mechanism and strength. Adhesive stability, the effect of heat on adhesive strength, and the ability of tissue to adhere to artificial materials were also clarified.

Real-time subject-specific analyses of dynamic internal tissue loads in the residual limb of transtibial amputees - Corrected Proof

2010-01-14

Abstract: Transtibial amputation (TTA) prosthetic-users may risk the integrity of their residuum while trying to maintain everyday activities. Compression of the muscle flap between the truncated bones and the prosthetic socket may cause pressure ulcers and deep tissue injury (DTI). We hypothesize that mechanical stresses in the muscle flap are higher when walking over complex terrains than during plane gait, and so, the residuum could be at risk for DTI when walking over these terrains. Accordingly, we evaluated internal soft tissue stresses in the residuum at the vicinity of the tibia in 18 prosthetic-users (7 vascular, 11 traumatic). For this purpose, we developed a portable monitor that calculated subject-specific internal stresses in the residuum in real-time. Each subject was studied while walking on plane floor, grass, stairs and slope. We found that internal stresses were the highest while subjects descended a slope, during which internal peak and root mean square (RMS) stresses were approximately 40% and 50% greater than in plane gait, respectively. Peak and RMS stresses calculated while descending a slope were approximately 2 times higher for the sub-group of vascular subjects compared to traumatic, but were similar between the two sub-groups for other ambulation tasks. Overall, the present internal stress monitor is a practical tool for real-time evaluation of internal stresses in the residuum of TTA prosthetic-users in the clinical setting or outdoors. Pending integration of appropriate dynamic tissue injury thresholds, the device can be utilized for alerting to the danger of DTI.

Using in-depth investigations to identify transportation safety issues for wheelchair-seated occupants of motor vehicles - Corrected Proof

Lawrence W. Schneider, Kathleen D. Klinich, Jamie L. Moore, Joel B. MacWilliams — 2009-10-05

Abstract: In-depth investigations of motor-vehicle crashes involve detailed inspection, measurement, and photodocumentation of vehicle exterior and interior damage, evidence of belt-restraint use, and evidence of occupant contacts with the vehicle interior. Results of in-depth investigations thereby provide the most objective way to identify current and emerging injury problems and issues in occupant safety and crash protection, and provide important feedback on the real-world performance of the latest restraint-system and vehicle crashworthiness technologies. To provide an objective understanding of real-world transportation safety issues for wheelchair-seated travelers, the University of Michigan Transportation Research Institute (UMTRI) has been conducting and assembling data from in-depth investigations of motor-vehicle crashes and non-crash adverse moving-vehicle incidents, such as emergency vehicle braking, turning, and swerving, in which there was at least one vehicle occupant sitting in a wheelchair. The results of 39 investigations involving 42 wheelchair-seated occupants have been assembled and entered into a wheelchair-occupant crash/injury database. In addition, a biomechanical analysis of each case has been performed to identify key safety issues for wheelchair-seated travelers.The wheelchairs of 34 of the 42 occupants who were seated in wheelchairs while traveling in motor vehicles were effectively secured by either a four-point, strap-type tiedown system or a docking securement device, and all but one of these properly secured wheelchairs remained in place during the crash or non-collision event. However, 30 of the 42 occupants were improperly restrained, either because of non-use or incomplete use of available belt restraints, or because the belt restraints were improperly positioned on the occupant's body. Twenty-six of the 42 occupants sustained significant injuries and 10 of these occupants died as a direct result of injuries sustained, or from complications resulting from those injuries. These findings, when combined with the analyses of the individual cases, point to a need for better driver and caregiver education and training on how to properly secure wheelchairs and position belt restraints on wheelchair-seated passengers. They also point to a need for improved restraint systems used by wheelchair-seated drivers, and a need for wheelchair designs that facilitate the proper use and positioning of vehicle-anchored belt restraints.

Reducing non-collision injuries in special transportation services by enhanced safety culture - Corrected Proof

Anders Wretstrand, Jan Petzäll, Per-Olof Bylund, Torbjörn Falkmer — 2009-09-28

Abstract: Previous research has pointed out that non-collision injuries occur among wheelchair users in Special Transportation Services (STS – a demand-responsive transport mode). The organization of such modes is also quite complex, involving both stakeholders and key personnel at different levels. Our objective was therefore to qualitatively explore the state of safety, as perceived and discussed within a workplace context. Focus groups were held with drivers of both taxi companies and bus companies.The results indicated that passengers run the risk of being injured without being involved in a vehicle collision. The pertinent organizational and corporate culture did not prioritize safety. The drivers identified some relatively clear-cut safety threats, primarily before and after a ride, at vehicle standstill. The driver's work place seemed to be surrounded with a reactive instead of proactive structure.We conclude that not only vehicle and wheelchair technical safety must be considered in STS, but also system safety. Instead of viewing drivers’ error as a cause, it should be seen as a symptom of systems failure. Human error is connected to aspects of tools, tasks, and operating environment. Enhanced understanding and influence of these connections within STS and accessible public transport systems will promote safety for wheelchair users.

WC19: A wheelchair transportation safety standard—Experience to date and future directions - Corrected Proof

Miriam A. Manary, Nichole L. Ritchie, Lawrence W. Schneider — 2009-09-27

Abstract: ANSI/RESNA WC19 (i.e., WC19) is a voluntary standard that specifies design and performance requirements for wheelchairs that are suitable for use as seats in motor vehicles. The guiding principles for the standard originate from automotive crash-protection principles that are effective in reducing occupant injuries and fatalities. In addition to frontal-impact testing of wheelchairs, the standard includes tests for securement-point accessibility, tiedown-strap clear paths, lateral stability, and accommodation of vehicle-anchored belt restraints. Results from testing wheelchairs to WC19 reveal that the most common wheelchair problems include: a lack of structural integrity during frontal-impact loading; sharp rigid edges; and wheelchair structures that interfere with achieving proper positioning of vehicle-anchored belt restraints. Data from 8 years of experience with WC19 indicate where changes are needed to further improve transportation safety for wheelchair-seated travelers. These include expanding WC19 to include wheelchairs for smaller children who require a five-point harness restraint, and requiring wheelchairs to achieve a minimal rating for the ease of achieving proper positioning of vehicle-anchored belt restraints.

Injuries in special transport services—Situations and risk levels involving wheelchair users - Corrected Proof

Anders Wretstrand, Per-Olof Bylund, Jan Petzäll, Torbjörn Falkmer — 2009-09-01

Abstract: Previous research has shown that wheelchair-seated passengers using special transportation services (STS) have been injured without being involved in a vehicle crash. In order to estimate incident rate and societal costs for these vehicle-related injuries, the focus needs to be adjusted towards a traveler/incident-oriented perspective. The aim of the project was to utilize such a perspective, related to travelers using STS in Sweden.In order to address the chosen perspective, a mixed method approach was used, involving quantitative as well as qualitative research techniques applied on four different sets of data: one hospital-based record, two sets of STS incident report databases, and interviews with wheelchair-seated STS passengers.The results showed that the injury incidence rate in STS is considerable, i.e. 10 per 100,000 trips. However, this high incidence rate is not due to road traffic collisions, but to non-collision injury incidents involving many elderly and frail passengers, who easily sustain traumas ranging from minor to moderate. The costs were estimated to be 23 million USD per annum or 14 USD per trip. Results suggest that future injury prevention measures should focus on safety in boarding and alighting procedures, as well as the continuing development of WTORS.

Characterization of pediatric wheelchair kinematics and wheelchair tiedown and occupant restraint system loading during rear impact - Corrected Proof

Susan I. Fuhrman, Patricia Karg, Gina Bertocci — 2009-04-24

Abstract: This study characterizes pediatric wheelchair kinematic responses and wheelchair tiedown and occupant restraint system (WTORS) loading during rear impact. It also examines the kinematic and loading effects of wheelchair headrest inclusion in rear impact. In two separate rear-impact test scenarios, identical WC19-compliant manual pediatric wheelchairs were tested using a seated Hybrid III 6-year-old anthropomorphic test device (ATD) to evaluate wheelchair kinematics and WTORS loading. Three wheelchairs included no headrests, and three were equipped with slightly modified wheelchair-mounted headrests. Surrogate WTORS properly secured the wheelchairs; three-point occupant restraints properly restrained the ATD. All tests used a 26km/h, 11g rear-impact test pulse. Headrest presence affected wheelchair kinematics and WTORS loading; headrest-equipped wheelchairs had greater mean seatback deflections, mean peak front and rear tiedown loads and decreased mean lap belt loads. Rear-impact tiedown loads differed from previously measured loads in frontal impact, with comparable tiedown load levels reversed in frontal and rear impacts. The front tiedowns in rear impact had the highest mean peak loads despite lower rear-impact severity. These outcomes have implications for wheelchair and tiedown design, highlighting the need for all four tiedowns to have an equally robust design, and have implications in the development of rear-impact wheelchair transportation safety standards.

Retrospective review of adverse incidents involving passengers seated in wheeled mobility devices while traveling in large accessible transit vehicles - Corrected Proof

Karen L. Frost, Gina Bertocci — 2009-04-23

Abstract: Objective: Characterize wheeled mobility device (WhMD) adverse incidents on large accessible transit vehicles (LATVs) based on vehicle motion, WhMD activity during incident, incident scenario and injury.Design: Retrospective records review.Subjects/patients: WhMD passengers traveling on LATVs while remaining seated in their.Methods: Adverse incidents characterized based on vehicle motion, WhMD activity during incident, and incident scenario. Injury characterized based on outcome, medical attention sought, vehicle activity, WhMD activity and incident scenario.Results: 115 WhMD-related incident reports for years 2000–2005 were analyzed. Most incidents occurred when the LATV was stopped (73.9%), during ingress/egress (42.6%), and at the securement station (33.9%) when the LATV was moving. The combination of WhMD tipping and passenger falling (43.4%) occurred most frequently, and was 1.8 times more likely to occur during ingress/egress than at the securement station. One-third (33.6%) of all incidents resulted in injury, and injuries were equally distributed between ingress/egress (43.6%) and at the securement station (43.6%).Conclusions: WhMD users have a greater chance of incurring injury during ingress/egress than during transit. Research is needed to objectively assess real world transportation experiences of WhMD passengers, and to assess the adequacy of existing federal legislation/guidelines for accessible ramps used in public transportation.

Development and validation of a computer crash simulation model of an occupied adult manual wheelchair subjected to a frontal impact - Corrected Proof

R. Dsouza, G. Bertocci — 2009-03-02

Abstract: Wheelchairs are primarily designed for mobility and are not necessarily intended for use as motor vehicle seats. However, many wheelchairs serve as vehicle seats for individuals unable to transfer to a vehicle seat. Subjecting wheelchairs to sled testing, in part establishes the crashworthiness of wheelchairs used as motor vehicle seats. Computer simulations provide a supplemental approach for sled testing, to assess wheelchair response and loading under crash conditions. In this study a nonlinear, dynamic, computer model was developed and validated to simulate a wheelchair and occupant subjected to a frontal impact test (ANSI/RESNA WC19). This simulation model was developed utilizing data from two frontal impact 20g/48km/h sled tests, which consisted of identical, adult manual wheelchairs secured with 4-point tiedowns, occupied with a 50th percentile adult male anthropomorphic test device (ATD), restrained with a 3-point occupant restraint system. Additionally, the model was validated against sled data using visual comparisons of wheelchair and occupant kinematics, along with statistical assessments of outcome measures. All statistical evaluations were found to be within the acceptance criteria, indicating the model's high predictability of the sled tests. This model provides a useful tool for the development of crashworthy wheelchair design guidelines, as well as the development of transit-safe wheelchair technologies.