Wheelchair Seat Cushions Research Articles

Study of castor oil‐based auxetic polyurethane foams for cushioning applications

AbstractThis work involves the study of mechanical and antibacterial properties of auxetic polyurethane (APU) foams synthesized using castor oil (CO) to ascertain their suitability as seat cushions in wheelchairs. Firstly, CO‐based PU foams (PU‐CO) were synthesized by substituting 25% synthetic polyol with CO in a polyol blend. Conventional PU foams and PU‐CO foams were then converted to auxetic foams using triaxial compression and heating. The chemical composition, microstructure and thermal, mechanical and antibacterial properties of the foams were analyzed. It was found that addition of CO improved the antibacterial and mechanical properties of the foams. CO‐based APU (CO‐APU) foams showed highest compression strength and storage modulus. An increase in thermal stability of PU‐CO was also observed as compared to PU foams. These CO‐APU foams could be a better alternative to conventional PU foams for wheelchair seat cushions and in hospital bed applications. © 2021 Society of Industrial Chemistry.

Evaluation of interface pressure and temperature management in five wheelchair seat cushions and their effects on user satisfaction

BackgroundFactors such as the manufacturing materials, shape or even the mechanical and thermal response of sitting Pressure Redistribution Support Surfaces (PRSS) can be potential contributors to pressure ulcers. However, few studies have compared a number of characteristics of the most frequently used devices. ObjectiveTo compare three potential contributors to pressure ulcers in five commercial PRSS: pressure redistribution, temperature and perceived comfort. Method: Study with a cross-over randomized design in healthy volunteer participants. Data was collected in a temperature and relative humidity controlled environment. To assess thermal response, the temperature (Flir-E60) of the region of interest was captured before and after use of each PRSS for further analysis. The region of interest was the gluteal zone. To assess the pressure redistribution a pressure mat (XSensor®) was used between the 5 cushion and each study participant using a standardized method. Finally, a subjective perception questionnaire recorded comfort, adaptability and thermal sensation parameters. Data analysis levels of significance were set at 0.05. ResultsA total of 22 participants completed the assessments. There were no statistically significant differences in baseline temperatures between PRSS (>0.05). Pressure redistribution analysis showed significant differences between all PRSS in all variables evaluated except in the maximum and peak pressure index al sacrum. The subjective assessment suggested no major user-perceived differences between PRSS. ConclusionSeat cushions made of open cell polyurethane foam blocks of variable hardness and the horseshoe cushion (also open cell polyurethane foam) seem to provide a more effective pressure relief characteristic than those injected with polyurethane foam and gel in most of the studied pressure variables. However, the cushions provide similar thermal response and perceived comfort.

Implementing local cooling to increase skin tolerance to ischemia during normal seating in people with spinal cord injury

The purpose of this study was to investigate the effectiveness of local cooling in reducing reactive hyperemia after ischemia at the ischial tuberosities for people with spinal cord injury (SCI) during normal seating. The degree of the reactive hyperemic response is indicative of the extent of cellular stress caused by the ischemia. We hypothesized that reactive hyperemic skin blood flow (SBF) responses will be lower when local cooling is implemented by the wheelchair seat cushion. This study used a repeated measures design, and each subject underwent two conditions: normal seating with temperature control ‘on’ (cooling) and ‘off’ (non-cooling) for 30 min. Twenty-three participants with traumatic SCI were recruited. SBF and skin temperature were collected before, during and after seating. SBF signals were processed with short-time Fourier analyses to examine the underlying vascular control mechanisms, including the following (corresponding frequency bands): metabolic (0.0095–0.02 Hz), neurogenic (0.02–0.05 Hz), and myogenic (0.05–0.15 Hz) spectral densities. Our results showed that with cooling, skin temperature decreased (range −0.4 ~ −3.1 °C, p = 0.002), and reactive hyperemia parameters (normalized peak SBF and perfusion area) were reduced (p = 0.02, p = 0.033, respectively). In addition, changes in normalized peak SBF (non-cooling – cooling) was moderately correlated with changes in normalized metabolic and neurogenic spectral densities. Our findings suggested that local cooling has a positive effect on reducing the cellular stress caused by ischemia during normal seating. Metabolic and neurogenic SBF control mechanisms may play a minor role. Further exploration of the effect of temperature control on pressure injury prevention is warranted.

Prevalence and factors associated with a higher risk of neck and back pain among permanent wheelchair users: a cross-sectional study.

Cross-sectional study. To determine the prevalence of, and factors associated with, spinal pain among wheelchair users. Four Spanish hospitals specialized in providing care for wheelchair users. Persons who had used a wheelchair for a median (IRQ) of 10 (5;19) years, 27% of them due to reasons other than spinal cord injury, were recruited consecutively (n = 750). Data on 43 demographic, psychosocial, ergonomic, and clinical variables were collected, and analyzed. Main outcome measures were: point prevalence of neck (NP), thoracic (TP), low back pain (LBP), and pain at any spinal level (PASL); and factors associated with them. Point prevalence was 56% for NP, 54% for TP, 45% for LBP, and 76% for PSAL. PASL was associated with a lower quality of life (OR (95% CI) 0.91 (0.86; 0.97)). Multivariable regression models showed that the main factors associated with significant pain (≥1.5 VAS points) were: (a) For NP: cervical spinal injury and wheelchair seat cushion thickness, (b) For TP: thoracic spinal injury and sagittal index, (c) For LBP: thoracic or lumbar spinal injury, with some sensitivity remaining, (d) For PASL: being female, living alone, and using a non-power wheelchair. Discrimination (AUC) of these models ranged between 0.638 and 0.818. p-values in the Hosmer-Lemeshow test ranged between 0.420 and 0.701. Prevalence of spinal pain among wheelchair users is high. It is associated with a lower quality of life. Future studies should assess whether using a power wheelchair affects PASL, and if the thickness of seat cushion affects NP. Spanish Back Pain Research Network.

FINITE ELEMENT PREDICTION OF SUB-DERMAL TISSUE STRESSES OF THE BUTTOCKS DURING WHEELCHAIR PROPULSION

Pressure ulcers, involving sub-dermal tissue damage and originating in deep tissue injury (DTI), have attracted much attention of physicians and researchers for three decades. Finite element (FE) model is a very efficient tool to investigate internal stresses and strains in human body that induce pressure ulcers. However, there was scarce report available to explore stresses distribution in human buttocks during manual wheelchair propulsion. A three-dimensional (3D) comprehensive FE model, incorporating ischial tuberosities (ITs), muscle, fat, and custom-contoured cushion (CCC), was developed to investigate internal stress distribution in soft tissue of the buttocks. Based on the FE model, pressure distribution under ITs in static sitting and during different wheelchair propulsions is studied. Internal stresses in fat and muscle were about three times and five times higher than that on cushion surface in terms of static sitting and wheelchair propulsion. All peak pressures under wheelchair propulsion were higher than those of static sitting, and peak pressures went on increasing with increase of wheelchair movement speed. This method based on the comprehensive FE model allowed for the optimization of wheelchair seat cushion design.

Orthotic-Style Off-Loading Wheelchair Seat Cushion Reduces Interface Pressure Under Ischial Tuberosities and Sacrococcygeal Regions

ObjectiveTo assess the efficacy of an off-loading wheelchair seat cushion in removing pressure from high-risk ischial tuberosities and the coccyx/sacrum in wheelchair sitting. DesignRepeated-measures design. SettingPrivate research laboratory. ParticipantsManual wheelchair users with chronic spinal cord injuries (N=10). InterventionsThree configurations of an off-loading wheelchair seat cushion compared with a flotation style (10-cm air inflation) wheelchair seat cushion. Main Outcome MeasuresOutcome measures included peak pressure index (PPI), ischial tuberosity peak pressures, and the dispersion index or ratio of pressures under the ischial and sacral regions to the total of all pressures recorded. ResultsPPI and ischial tuberosities peak pressure ranged from a low of 39±18 and 68±46mmHg in the fully off-loaded cushion to a high of 97±30 and 106±34mmHg, respectively, for the flotation style cushion (2-way analysis of variance main effect across 4 conditions, P<.001). Dispersion index ranged from a low of 8%±3% in the fully off-loaded cushion to a high of 16%±3% in the flotation style cushion. Pairwise comparisons yielded significance in all cushion-pair analyses (P<.05 after multiple corrections). ConclusionsThe force-removal approach of this orthotic off-loading cushion design effectively reduces a known extrinsic risk factor for pressure ulcers—interface pressure—in the high-risk ischial tuberosity and sacral/coccygeal regions of the buttocks.

Experiments and Evaluation of Body Pressure Distribution on Wheelchair Cushion

To study the relationship between wheelchair cushion shape and seat cushion comfort. By measuring sitting pressure distributions on wheelchair cushions with different shape, indices of sitting pressure such as the contact area, maximum sitting pressure were discussed along with method for subjective evaluation and objective test combination to analyze the relationship between seat cushion shape and seat cushion comfort. The experimental results from subjective assessment on three kinds of seat cushion indicate that the cushion shape is an important factor affecting seating comfort .The experimental results from objective assessment indicate that the contact area and maximum sitting pressure can preferably reflect the comfort of seat cushion and be used to evaluate the comfort of seat cushion.

Interface shear and pressure characteristics of wheelchair seat cushions

Pressure ulcer incidence rates have remained constant despite advances in support surface technology. Interface shear stress is recognized as a risk factor for pressure ulcer development and is the focus of many shear reduction technologies incorporated into wheelchair cushions; however, shear reduction has not been quantified in the literature. We evaluated 21 commercial wheelchair seat cushions using a new methodology developed to quantify interface shear stress, interface pressure, and horizontal stiffness. Interface shear stress increased significantly with applied horizontal indenter displacement, while no significant difference was found for interface pressure. Material of construction resulted in significant differences in interface shear stress, interface pressure, and horizontal stiffness. This study shows that the existing International Organization for Standardization (ISO) 16840-2 horizontal stiffness measure provides similar information to the new horizontal stiffness measure. The lack of a relationship between interface shear stress and the overall horizontal stiffness measure, however, suggests that a pressure and shear force sensor should be used with the ISO 16840-2 horizontal stiffness measure to fully quantify a cushion's ability to reduce interface shear stress at the patient's bony prominences.

A Randomized Clinical Trial on Preventing Pressure Ulcers with Wheelchair Seat Cushions

To determine the efficacy of skin protection wheelchair seat cushions in preventing pressure ulcers in the elderly nursing home population. Clinical trial with participants assigned at random to a skin protection or segmented foam cushion. Two hundred thirty-two participants were recruited between June 2004 and May 2008 and followed for 6 months or until pressure ulcer incidence. Twelve nursing homes. Nursing home residents aged 65 and older who were using wheelchairs for 6 or more hours per day and had a Braden score of 18 or less and a combined Braden activity and mobility score of 5 or less. Participants were recruited from a referred sample. All participants were provided with a fitted wheelchair and randomized into skin protection (SPC, n=113) or segmented foam (SFC, n=119) cushion groups. The SPC group received an air, viscous fluid and foam, or gel and foam cushion. The SFC group received a 7.6-cm crosscut foam cushion. Pressure ulcer incidence over 6 months for wounds near the ischial tuberosities (IT ulcers) were measured. Secondary analysis was performed on combined IT ulcers and ulcers over the sacrum and coccyx (sacral ulcers). One hundred eighty participants reached a study end point, and 42 were lost to follow-up. Ten did not receive the intervention. There were eight (6.7%) IT ulcers in the SFC group and one (0.9%) in the SPC group (P=.04). There were 21 (17.6%) combined IT and sacral ulcers in the SFC group and 12 (10.6%) in the SPC group (P=.14). Skin protection cushions used with fitted wheelchairs lower pressure ulcer incidence for elderly nursing home residents and should be used to help prevent pressure ulcers.

Treatment of Gibbus Deformity Associated with Myelomeningocele in the Young Child with Use of the Vertical Expandable Prosthetic Titanium Rib (VEPTR)

Approximately 8% to 21% of patients with myelomeningocele have an associated kyphotic deformity, most commonly in the upper lumbar or thoracolumbar area1-3. The natural history of congenital rigid kyphosis, or gibbus deformity, is rapid progression in early childhood1-6. The apex of the deformity is most frequently located in the middle and upper lumbar spine3,7 and is associated with vertebral anomalies, a sharp apical angulation, and the potential for skin breakdown over the deformity. It is the most common type of kyphosis associated with myelomeningocele4. A number of strategies have been used for the treatment of rigid kyphosis. For patients with myelomeningocele, conservative treatment with modified wheelchair seat cushions and bracing is relatively ineffective6,8-10. Bracing does not prevent progression of the deformity and may contribute to skin breakdown. Surgery has therefore been recommended as the treatment of choice. Since it was first described by Sharrard in 196811, osteotomy for the resection of the vertebral bodies (kyphectomy) and spinal fusion has been the standard surgical approach for the treatment of this kyphotic deformity3,4,7-9,12-22. Although the concept of vertebral resection is widely accepted, there are no consistent recommendations for the timing of surgery, the extent of the resection and fusion, and the ideal type of instrumentation used. Independent of the surgical technique, most authors agree that the rate of complications associated with correction of this deformity is high. Additionally, spinal instrumentation and fusion in an immature spine may lead to crankshaft changes in the spine17. In 2004, Campbell et al.23 described the use of the Vertical Expandable Prosthetic Titanium Rib (VEPTR; Synthes Spine, West Chester, Pennsylvania) for …

Comparative study of pressure distribution at the user-cushion interface with different cushions in a population with spinal cord injury

Background Few studies have offered comparative information on the mechanical characteristics of different wheelchair seat cushions. The objective of the present study was to compare the benefits of the wheelchair seat cushions most frequently used in a population of patients with spinal cord injury in terms of pressure distribution and contact surface at the user-cushion interface. Methods Each one of 48 patients with spinal cord injury was seated in his or her own wheelchair on the four models of cushions analyzed (low-profile air, high-profile air, dual-compartment air, and gel and firm foam), which were presented in randomized order. The pressure distribution readings and support surface area of the user-cushion interface were obtained with a matrix of piezocapacitive sensors. Findings The dual-compartment air cushion yielded lower readings for all pressure parameters analyzed ( P max, P mean, P sd, and P isch) than the other three cushion models ( P < 0.05). The best surface parameter results ( S tot, S > 60 and % S > 60) also were obtained with the dual-compartment air cushion ( P < 0.05). Interpretation In the sample analyzed, the dual-compartment air cushion was the cushion with the best pressure distribution and largest contact surface of the user-cushion interface compared to the other three cushions studied.

A New Method to Generate a Patient-Specific Finite Element Model of the Human Buttocks

Finite element (FE) models are very efficient tools to study internal stresses in human structures that induce severe pressure sores. Unfortunately, methods currently used to generate FE models are not suitable for clinical application involving wheelchair users. A clinical-oriented method, based on calibrated-biplanar radiographs, was therefore developed to generate a subject-specific FE model of the buttocks in a non-weighted sitting position. The model was then used to analyze the stress distribution within the buttocks and compare two wheelchair seat cushions designs. Additional radiographs and pressure measurements in a weighted sitting position were acquired to validate the FE model experimentally. Results from the FE model were in good agreement with experimental data and related literature. An internal peak pressure of 45.3 kPa was observed while seated on a flat foam cushion, corresponding to an interface pressure of 23.6 kPa. Both pressures occurred underneath the ischial tuberosities. When compared to the flat foam cushion, the contoured foam cushion reduced internal and interface peak pressures by 18% and 33%, respectively. The method developed in this study has a great potential for clinical use. The FE model, by predicting realistic stress distributions, allows for the selection of a convenient wheelchair seat cushion.

Lessons Learned from an Old Acquaintance

Lessons Learned from an Old Acquaintance

A guide to evaluating different wheelchair seat cushions

Over the years, there has been a considerable increase in the number and variety of wheelchair seat cushions. People required to select a cushion are faced with a confusing and often misleading array of commercial literature. The cost of these products range from less than £100 to several hundred pounds, so the importance of a logical approach to their selection cannot be overstated. Inappropriate selection not only wastes capital resources, but it can also be very harmful to the patient. Although the effectiveness of a wheelchair cushion is best evaluated through clinical trials, these are expensive to conduct and in the case of new products, such evidence is not readily available. In order to overcome this drawback, researchers have developed experimental methods of evaluation based upon existing knowledge of pressure ulcer aetiology. This article describes the most common methods, along with a new technique known as pressure relief index.

Ein neues Verfahren zur patientenorientierten Zuordnung von Rollstuhlsitzkissen auf Basis von standardisierten Prüfverfahren / A novel method for patient-oriented assignment of wheelchair cushions based on standardized laboratory testing procedures

A wheelchair seat cushion represents the interface between the wheelchair and the wheelchair driver and has to manage the force transmission and the stabilization between both of them. An additional very important requirement is the prevention of pressure ulcers by pressure relief and the transfer of humidity and heat away from the patient. The allocation of a cushion to the patient happens normally on the base of a subjective description of the cushion without any transparent decision rules. Consequently the quality of this procedure could be improved by a better description of the cushion, based on standardized laboratory tests and by the development of decision tools helping to identify the main efforts of the user. This article describes a procedure that allows the allocation of wheelchair seat cushions based on the characteristic of cushions from standardized laboratory tests and on the brief description of the user. Additionally the existing principles for wheelchair cushions are listed, described and compared. The possibilities to develop structured decision tools for wheelchair cushions are discussed.

The Relationship Between Pressure Ulcer Incidence and Buttock-Seat Cushion Interface Pressure in At-Risk Elderly Wheelchair Users

Objective:To investigate the relation between pressure ulcer incidence and buttock-wheelchair seat cushion interface pressure measurements. Design:Secondary analysis of data from a randomized clinical trial. Setting:Skilled nursing facility. Patients:Thirty-two elderly patients (age, ⩾ 65yr), with Braden score ⩽ 18 and Braden mobility and activity subscale scorche ⩽ 5, who used wheelchairs ⩾ 6hr/d, were free of existing sitting-induced pressure ulcers, and weighed ⩽ 2501b. Interventions:Generic foam seat cushion or pressure-reducing seat cushion. Main Outcome Measures:The incidence of sitting-induced pressure ulcers over a 1- to 12-month period was compared with pressure measured between patients' buttocks and wheelchair seat cushions. A flexible pad with a 15 × 15 pressure sensor array was used to measure interface pressure. Results:Interface pressure measured on wheelchair seat cushions was higher (p ⩽ .01 for both peak pressure and average of highest 4 pressures) for patients who developed sitting-acquired pressure ulcers compared with those patients who did not. Conclusions:Results indicated that higher interface pressure measurements are associated with a higher incidence of sitting-acquired pressure ulcers for high-risk elderly people who use wheelchairs.

Finite element modeling of a wheelchair seat cushion

Finite element modeling of a wheelchair seat cushion

Clinical gait analysis of hip disarticulation amputees

To assess the efficacy of an off-loading wheelchair seat cushion in removing pressure from high-risk ischial tuberosities and the coccyx/sacrum in wheelchair sitting.Repeated-measures design.Private research laboratory.Manual wheelchair users with chronic spinal cord injuries (N=10).Three configurations of an off-loading wheelchair seat cushion compared with a flotation style (10-cm air inflation) wheelchair seat cushion.Outcome measures included peak pressure index (PPI), ischial tuberosity peak pressures, and the dispersion index or ratio of pressures under the ischial and sacral regions to the total of all pressures recorded.PPI and ischial tuberosities peak pressure ranged from a low of 39±18 and 68±46mmHg in the fully off-loaded cushion to a high of 97±30 and 106±34mmHg, respectively, for the flotation style cushion (2-way analysis of variance main effect across 4 conditions, P<.001). Dispersion index ranged from a low of 8%±3% in the fully off-loaded cushion to a high of 16%±3% in the flotation style cushion. Pairwise comparisons yielded significance in all cushion-pair analyses (P<.05 after multiple corrections).The force-removal approach of this orthotic off-loading cushion design effectively reduces a known extrinsic risk factor for pressure ulcers—interface pressure—in the high-risk ischial tuberosity and sacral/coccygeal regions of the buttocks.

Dynamic interface pressure between seated users and their wheelchairs

Little is known about the dynamic pressure distribution changes that take place on the sitting surface of a wheelchair while one propels oneself on a level surface. An understanding of these dynamic pressure changes may influence the design of wheelchair seat cushions to minimize pressure sores in wheelchair users. This research investigated the dynamic interfacial pressure changes on the seated wheelchair user during short bursts of locomotion on a level surface. The pilot project included only able-bodied subjects who sat in sling-seat wheelchairs. Pneumatic bladders arranged in a flexible grid matrix (50 elements covering a 7.5″ × 15″ area) were instrumented with miniature piezoresistive pressure transducers and placed between the user and the wheelchair seat. One half of the subject/seat interface was instrumented: one-half-inch-thick foam covered the remaining half of the seat. Dynamic pressure distribution in the left and right halves was measured in separate trials for every subject. Each sensor element was sampled 10 times per second during the time it took the subject to traverse approximately 25 feet from start to stop. A trial lasted 5.6 seconds on average. The greatest shift in center of pressure observed for any trial was 3.15 inches. The lowest, static, and highest average pressures obtained were 14.2 mmHg, 27.8 mmHg, and 36.5 mmHg, respectively. The lowest, static, and highest maximum pressures were 42.0 mmHg, 135.0 mmHg, and 178.8 mmHg, respectively. There was no significant difference in location between the lowest and highest maximum pressures. The sizes of the buttock area in which pressure exceeded 35 mmHg were determined for smallest area, static, and largest area conditions. These were 2.25 sq.in., 27.0 sq.in, and 47.25 sq.in., respectievly.

Development and evaluation of a universal contoured cushion.

A new wheelchair seat cushion has been developed which reduces the ischaemia producing forces and redistributes them to the more tolerant areas of the posterior thighs and lateral gluteal muscles. The cushion is fabricated of foam materials and designed to stabilise the pelvis and promote proper spinal-pelvic alignment. Pressure measurements were recorded at the skin cushion interface for 66 subjects while seated on the cushion in their own wheelchair. The cushion was considered effective if maximum interface pressures recorded were: coccyx: less than 20 mmHg, ischii: less than 65 mmHg, trochanters: less than 70 mmHg, and posterior thighs: less than 80 mmHg. The cushion was considered ineffective if the interface pressure at any one location exceeded these criteria. The cushion was found effective for 52 of the subjects. The cushion was more effective (90 per cent versus 58 per cent) for subjects without certain skeletal deformities (pelvic obliquity, bony resections). Eighty-three per cent of the respondents who were followed on the cushion reported that they preferred the cushion to their previous cushions with improved posture, balance and comfort being the most commonly cited reasons. This study has shown the cushion to be a preferred alternative to other commercially available wheelchair cushions for those who are paraplegic.