Pressure distribution at the seating interface of custom-molded wheelchair seats: effect of various materials

The clinical effectiveness of custom-contoured seating for wheelchair users with neuromuscular disorders: a scoping review

Despite its widespread use, the clinical effectiveness of custom-contoured wheelchair seating for individuals with neuromuscular disorders remains unclear. A scoping review was conducted using PubMed, Scopus, and Web of Knowledge databases in November 2021 and updated April 2022. A total of 17 full text articles were included. Discussion themes were grouped based on three outcomes of interest: (1) posture and musculoskeletal deformity, (2) quantitative measures of body structures and functions, and (3) qualitative perceptions, opinions, and quality of life indicators. This review highlighted the lack of literature exploring the impact of custom-contoured seating on cardiopulmonary function, pressure injury management, and upper limb function; although, there was no indication that risk is increased compared to alternative seating and it performed well in terms of perceived user satisfaction, comfort, and function. The findings also demonstrated immediate benefits to postural alignment, although, the longitudinal effect on progression of musculoskeletal deformity compared to alternative seating is more ambiguous. This review aimed to scope the evidence-base for custom-contoured seating for wheelchair users with neuromuscular disorders to synthesize information from the existing literature, inform current practice, and identify knowledge gaps for further experimental investigation.

Safety Assessment of Rehabilitation Robots: A Review Identifying Safety Skills and Current Knowledge Gaps

The assessment of rehabilitation robot safety is a vital aspect of the development process, which is often experienced as difficult. There are gaps in best practices and knowledge to ensure safe usage of rehabilitation robots. Currently, safety is commonly assessed by monitoring adverse events occurrence. The aim of this article is to explore how safety of rehabilitation robots can be assessed early in the development phase, before they are used with patients. We are suggesting a uniform approach for safety validation of robots closely interacting with humans, based on safety skills and validation protocols. Safety skills are an abstract representation of the ability of a robot to reduce a specific risk or deal with a specific hazard. They can be implemented in various ways, depending on the application requirements, which enables the use of a single safety skill across a wide range of applications and domains. Safety validation protocols have been developed that correspond to these skills and consider domain-specific conditions. This gives robot users and developers concise testing procedures to prove the mechanical safety of their robotic system, even when the applications are in domains with a lack of standards and best practices such as the healthcare domain. Based on knowledge about adverse events occurring in rehabilitation robot use, we identified multi-directional excessive forces on the soft tissue level and musculoskeletal level as most relevant hazards for rehabilitation robots and related them to four safety skills, providing a concrete starting point for safety assessment of rehabilitation robots. We further identified a number of gaps which need to be addressed in the future to pave the way for more comprehensive guidelines for rehabilitation robot safety assessments. Predominantly, besides new developments of safety by design features, there is a strong need for reliable measurement methods as well as acceptable limit values for human-robot interaction forces both on skin and joint level.

Tissue matters: In-vivo tissue properties of persons with spinal cord injuries to inform clinical models for pressure ulcer prevention

The prevalence of pressure ulcers in patients with spinal cord injuries has been estimated to be between 30% and 47%. Individuals with spinal cord injuries sit for a majority of the time, increasing the risk of developing pressure ulcers in the buttocks and thighs due to large internal stresses. Human body models have been developed to study the formation of pressure ulcers, yet a persistent limitation in these models has been the material properties used to represent the soft tissues in the buttocks and thighs. Specifically, soft tissue material property data have not included wheelchair users, such as those with spinal cord injuries. The goals of this research were 1) to determine the in-vivo material properties of soft tissue in the thighs and buttocks of individuals with spinal cord injuries and 2) compare these to properties obtained from able-bodied people. Results indicated that the proximal and middle thigh regions of those who had a spinal cord injury were softer than the same regions as able-bodied individuals, while the distal thigh regions were stiffer. These findings are vital because they indicate that models developed using properties from able-bodied individuals will not produce internal stress or strain magnitudes that represent individuals who have a spinal cord injury. This information suggests that models should obtain material property data sets from their desired population. Human body models must represent the population being studied if they are to inform clinical assessments and make accurate patient predictions.

Viscoelastic epoxy foams by an aqueous emulsion foaming process

The research proposed an aqueous emulsion foaming process to produce a viscoelastic epoxy foam having a density of 0.33–0.36 g/cm3 from the polyamide–epoxy adduct, which uses a reverse ratio of epoxy and polyamide hardener. The process is simple, economical and uses no surfactant, thanks to the emulsifying ability of polyamide hardener. Firstly, the mixture of excess polyamide, epoxy and sodium bicarbonate was emulsified with distilled water using high-speed stirring to form dispersed epoxy droplets in water. Secondly, a solution of ammonium chloride was added, which reacted with sodium bicarbonate to produce carbon dioxide and ammonia gases dispersed in the epoxy emulsion. The expanding gases induced flocculation and partial coalescence of the epoxy droplets; sequentially water molecules were entrapped within them. Finally, a curing process was carried out to stabilise the foam morphology and structure. Two types of pore morphologies were observed: a large foam-pore generated from blowing-agent gases and a cell-wall pore formed from the vapourisation of entrapped water (as the void template). Porosity and pore morphologies depended on blowing-agent content, and the viscoelasticity was affected by the epoxy/polyamide ratio. The obtained viscoelastic foams showed a large number of interconnected cells and exhibited high compression set values.

Pressure Injuries in Medically Complex Children: A Review

Pressure injuries are a challenging problem in the care of medically complex children. Available evidence is limited, and there are theoretical reasons to use caution before extrapolating adult data, including key differences in body composition, common locations of pressure injury, and association with medical devices. The focus of this article will be to review the definition of a pressure injury and what is known about pathophysiology, prevention, recognition, staging, and treatment of pressure injuries in children with medical complexity.

Investigation of peak pressure index parameters for people with spinal cord injury using wheelchair tilt-in-space and recline: methodology and preliminary report

The purpose of this study was to determine the effect of the sensel window's location and size when calculating the peak pressure index (PPI) of pressure mapping with varying degrees of wheelchair tilt-in-space (tilt) and recline in people with spinal cord injury (SCI). Thirteen power wheelchair users were recruited into this study. Six combinations of wheelchair tilt (15°, 25°, and 35°) and recline (10° and 30°) were used by the participants in random order. Displacements of peak pressure and center of pressure were extracted from the left side of the mapping system. Normalized PPI was computed for three sensel window dimensions (3 sensels × 3 sensels, 5 × 5, and 7 × 7). At least 3.33 cm of Euclidean displacement of peak pressures was observed in the tilt and recline. For every tilt angle, peak pressure displacement was not significantly different between 10° and 30° recline, while center of pressure displacement was significantly different (P < .05). For each recline angle, peak pressure displacement was not significantly different between pairs of 15°, 25°, and 35° tilt, while center of pressure displacement was significantly different between 15° versus 35° and 25° versus 35°. Our study showed that peak pressure displacement occurs in response to wheelchair tilt and recline, suggesting that the selected sensel window locations used to calculate PPI should be adjusted during changes in wheelchair configuration.

Influence of girth strap placement and panel flocking material on the saddle pressure pattern during riding of horses

REASONS FOR PERFORMING STUDY

Saddle fit is well recognised as an important factor for the health and performance of riding horses. However, only few studies have addressed general effects of different saddle construction details within a group of horses.

OBJECTIVE

To assess the influence of girth strap placement, traditional vs. v-system, and panel flocking material, wool vs. synthetic foam, on the saddle pressure pattern during riding.

METHODS

Six horses were ridden by 3 riders in sitting and rising trot and sitting canter. Saddle pressure was measured with 3 different saddle variants: 1) wool flocked panels and traditional girthing (baseline); 2) wool flocked panels and v-system girthing; and 3) foam filled panels and traditional girthing. From the pressure data, a number of descriptive variables were extracted. These were analysed using ANCOVA models with horse, rider, saddle, seat (sitting/rising, trot only) and speed as independent variables.

RESULTS

With foam filled panels stride maximum pressures under the hind part of the saddle increased by 7-12% and the area under the saddle with a stride mean pressure >11 kPa increased by 114 cm(2) in trot and 127 cm(2) in canter. With v-system girthing, the latter variable also increased, but only by 53 and 38 cm(2) in trot and canter, respectively. In addition, stride maximum pressures under the front part of the saddle tended to increase (≤ 9%).

CONCLUSIONS

Both flocking material and girthing have a significant influence on the saddle pressure and should thus be considered in saddle fitting. Wool seems a better flocking material than foam of the type used in the current study. For girthing, traditional placement seems equally good if not better than the v-system. However, further studies are needed to show if these results are valid for a larger population of riding horses.

Design and milling manufacture of polyurethane custom contoured cushions for wheelchair users

BACKGROUND

The design of custom contoured cushions manufactured in flexible polyurethane foams is an option to improve positioning and comfort for people with disabilities that spend most of the day seated in the same position. These surfaces increase the contact area between the seat and the user. This fact contributes to minimise the local pressures that can generate problems like decubitus ulcers. The present research aims at establishing development routes for custom cushion production to wheelchair users. This study also contributes to the investigation of Computer Numerical Control (CNC) machining of flexible polyurethane foams.

METHOD

The proposed route to obtain the customised seat began with acquiring the user's contour in adequate posture through plaster cast. To collect the surface geometry, the cast was three-dimensionally scanned and manipulated in CAD/CAM software. CNC milling parameters such as tools, spindle speeds and feed rates to machine flexible polyurethane foams were tested. These parameters were analysed regarding the surface quality. The best parameters were then tested in a customised seat. The possible dimensional changes generated during foam cutting were analysed through 3D scanning. Also, the customised seat pressure and temperature distribution was tested.

RESULTS

The best parameters found for foams with a density of 50kg/cm(3) were high spindle speeds (24000 rpm) and feed rates between 2400-4000mm/min. Those parameters did not generate significant deformities in the machined cushions. The custom contoured cushion satisfactorily increased the contact area between wheelchair and user, as it distributed pressure and heat evenly.

CONCLUSION

Through this study it was possible to define routes for the development and manufacturing of customised seats using direct CNC milling in flexible polyurethane foams. It also showed that custom contoured cushions efficiently distribute pressure and temperature, which is believed to minimise tissue lesions such as pressure ulcers.

Seating and pressure ulcers: clinical practice guideline

Pressure ulcers (bedsores) often develop following prolonged sitting especially where people are immobile or are unable to feel discomfort due to injury or disease. This guideline provides health professionals with specific recommendations intended to minimise any risk of developing pressure ulcers when their clients are seated. The guideline covers sitting when people are acutely ill in hospital and, more commonly, where people have a long-term need for prolonged sitting for example after spinal injury. Particular focus is placed upon the need to make sure the physical size and shape of the seat is appropriate for the seated individual. Guidance is provided upon areas where seated individuals require information to help them minimise pressure ulcer development. The advantages and disadvantages of different cushion materials are described.

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.

Pressure-reducing cushions: perceptions of comfort from the wheelchair users' perspective using interface pressure, temperature and humidity measurements

INTRODUCTION

There are many static pressure-reducing cushions commercially available consisting of foams, gels, air or a combination of these. There is, however, little evidence available on their effectiveness to guide prescription. In practice, comfort tends to be a major factor in determining whether a pressure-reducing cushion will continue to be used, although it is unclear as to what determines comfort. The aim of this study was to assess if perceptions of comfort could be associated with the measurable parameters of interface pressure and temperature. This pilot study was undertaken in the community with individuals who were totally reliant upon a wheelchair for their mobility who each used a series of four different cushions for up to 7 days.

METHOD

The temperature and humidity characteristics of four commercially available pressure-reducing cushions of differing mediums were measured using data loggers for a continuous period of up to 7 days. Snap-shot interface pressure measurements were taken and perceptions of comfort were obtained via specifically designed questionnaires.

RESULTS

The cushions that wheelchair users found to be the most comfortable for them were not necessarily those, which provided them with the lowest interface pressures. If a cushion was discontinued by the wheelchair user, it was invariably a "softer" medium. Wheelchair users tended to acknowledge discomfort only after 2 days continuous use.

CONCLUSION

There are potential implications for clinical practice with respect to how cushions are issued to wheelchair-reliant individuals. Findings support the undertaking of a larger study.

Management of seating posture of children with cerebral palsy by using thoracic-lumbar-sacral orthosis with non-rigid SIDO frame

PURPOSE

To investigate the effects of a special seating device: Thoracic-lumbar-sacral orthosis with non-rigid SIDO frame (TLSO-SIDO) in non-ambulant children with cerebral palsy.

METHOD

A prospective study with matched pairs (the same subject pre- and post-intervention) was carried out. A comparison of the lateral view of thoracic-lumbar spine X-ray before and after TLSO-SIDO application was made. The assessment of changes in daily activities, posture was recorded by questionnaires. A total of 47 children with cerebral palsy at a mean age of 53.2 months +/- 30.1 SD were involved in the study; 15 (35.71%) of the 42 children showed significant problems in feeding at the beginning of the study period, they were identified as a special subgroup with feeding difficulties.

RESULTS

The mean pre-TLSO-SIDO thoracic kyphosis was 53.7 +/- 16.2 in Cobb angle, while the post-TLSO-SIDO thoracic kyphosis was 47.2 +/- 12.1. The lumbar lordosis was 21.3 +/- 13 and in the TLSO-SIDO 17.8 +/- 11.9. The majority of the children have shown improvement in the feeding items and in posture (trunk, head and extremities). The overall satisfaction of the parents with the TLSO-SIDO was very good, namely 3.972 +/- 0.796 on the 5-point analogue scale. We did not find a direct correlation with the improvement in the separate items and the overall satisfaction.

CONCLUSION

It is extremely difficult to measure the effect of the postural management on the development of children with cerebral palsy. According to the results of the study, regular application of the TLSO-SIDO in children with spastic cerebral palsy had a beneficial effect on feeding problems and on posture.

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.

Measuring seating pressure, area, and asymmetry in persons with spinal cord injury

The goal of this study was to measure characteristics of seat loading in manual wheelchair users with complete spinal cord injury (SCI). Pressure distribution on the seating area of 25 adult males with SCI and eight non-injured adult males was measured in a relaxed and an upright posture on a standardized hard surface. Subjects with SCI were also tested in their wheelchairs. Maximum pressure, contact area, area of the highest pressure, and three asymmetry indices were compared. Subjects with SCI have higher pressure distributed over a smaller area, have a much smaller contact area, and distribute the loading more asymmetrically than non-injured subjects. Upright posture only corrects for some loading problems, while the wheelchair corrects for more loading parameters. Routine clinical seat loading evaluation may lead to improved chair and cushion selection for patients with SCI and may even alert clinicians to patients at high risk for complications due to high or unbalanced loads.