Measuring the impact of cushion design on buttocks tissue deformation: An MRI approach

A systematic review of the effectiveness of pressure relieving cushions in reducing pressure injury

This systematic review seeks to gather and analyze the evidence on wheelchair pressure relieving cushions, and report on the optimal materials and designs for reducing pressure injury risk. The following research question guides this study: Which wheelchair cushions best reduce pressure injury risk? PIs continue to impact the health and function of wheelchairs users with significant mobility impairments. Pressure relieving cushions are typically prescribed to provide pressure relief in the pre-wound, wound, and post-wound phases. Presently, no published reviews analyze all of the commonly available cushion materials. Most comparison studies typically address a specific population such as spinal cord injury, or only a few styles of cushion design/materials. Results suggest air-cell cushions provide optimal pressure relief and shear reduction. Furthermore, small sample single cohort studies suggest off-loading cushions provide superior pressure relief beyond that of air-celled cushions but require additional research for greater generalizability.

Reducing pressure with the goal of improving outcomes: a retrospective chart review of cushion evaluations and recommendations at one seating clinic

PURPOSE

To describe the current seating recommendations made by a seating clinic for wheelchair users who presented with a Pressure Injury (PrI) or history of PrI.

METHODS

Retrospective review of electronic medical records of 133 adults who used a wheelchair as their primary means of mobility who had a cushion evaluation during which interface pressure mapping data was documented.

RESULTS

Clinicians adjusted 71% of participants' wheelchair cushions, including 49% who received a new cushion, and 37% of participants' wheelchairs. The most common adjustments besides receiving a new cushion were: addition of an underlay, adjusting the inflation of a cushion, and adjustments to the foot or back support of the wheelchair. Forty-five participants only received adjustments (i.e. no new cushion), while 23 participants only received education and feedback rather than equipment modifications. Those 23 participants had significantly lower Peak Pressure Index (PPI) than those who received equipment modifications (mean [95% CI] 76.7 [59.1, 94.3] versus 111.6 [102.1, 121.2] respectively, p = 0.001). The PPI was reduced by an average of 22.5 mmHg from the initial to final seating system amongst those who received modifications ([13.9-31.0], p<.001).

CONCLUSIONS

The seating clinicians considered interface pressure mapping in their decision-making and effectively reduced interface pressures with their interventions. Cushion replacement is important when someone presents with a PrI. However, adjusting an existing wheelchair cushion and/or seating system provides important additions and alternatives to consider for reducing interface pressure. There is also a role for education about proper use of equipment, weight shifts, and alternate seating surfaces.

Methodology to Investigate Effect of Prosthetic Interface Design on Residual Limb Soft Tissue Deformation

BACKGROUND

Residual limb discomfort and injury is a common experience for people living with lower limb amputation. Frequently, inadequate load distribution between the prosthetic device and the residual limb is the root cause of this issue. To advance our understanding of prosthetic interface fit, tools are needed to evaluate the mechanical interaction at the prosthetic interface, allowing interface designs to be evaluated and optimised.

OBJECTIVE

Present a methodology report designed to facilitate comprehension of the mechanical interaction between the prosthetic interface and the residual limb. As a pilot study, this methodology is used to compare a hands-on and hands-off interface for a single transtibial prosthesis user using secondary Magnetic Resonance Imaging (MRI) data.

METHODOLOGY

MRI data of the residual limb while wearing a prosthetic interface is segmented into a hard tissue and a skin surface model. These models are exported as stereolithography (STL) files. Two methods are used to analyse the interface designs. Firstly, CloudCompare software is used to compute the nearest vertex on the skin surface for every vertex on the compiled internal bony surface for both interface types. Secondly, CloudCompare software is used to compare registered skin surfaces of the residual limb while wearing the hands-on and hands-off interfaces.

FINDINGS

The maximum and minimum nearest distances between the internal bony surface and skin surface were similar between interface types. However, the distribution of nearest distances was different. When comparing the skin surface while wearing both interfaces, where the fit is more compressive can be visualized. For the dataset used in this study, the classic features of a hands-on Patella Tendon Bearing interface and hands-off pressure cast interface could be identified.

CONCLUSION

The methodology presented in this report may give researchers a further tool to better understand how interface designs affect the soft tissues of the residual limb.

OFF-LOADING PRESSURE RELIEF WITH FOAM CUT OUT CUSHIONS: EXPERIENCES FROM RANCHO LOS AMIGOS NATIONAL REHABILITATION CENTER

This paper explores the efficacy of the cushion fitting technique using foam cut out cushions for off-loading bony prominences in the sitting position, with a particular focus on reducing the high risk of developing pressure injuries among aging wheelchair users. This technique, historically employed at Rancho Los Amigos National Rehabilitation Center, has shown promising results in reducing pressure injuries for patients with spinal cord injuries. However, its widespread adoption remains limited. This manuscript aims to raise awareness about foam cut out cushions, its historical context, and its contemporary relevance by presenting customized solutions for individual patients with specific deformities. Key clinical points are highlighted, emphasizing the importance of skilled clinicians in the fitting process and the need to consider foam cut out cushions alongside other preventive measures. Case examples illustrate successful outcomes, demonstrating improved pelvic stability, posture, and off-loading of bony prominences. By promoting foam cut out cushions as a valuable cushioning option, this manuscript equips clinicians with knowledge to utilize this technique effectively.

PIPER adult comfort: an open-source full body human body model for seating comfort assessment and its validation under static loading conditions

Introduction: In this paper we introduce an adult-sized FE full-body HBM for seating comfort assessments and present its validation in different static seating conditions in terms of pressure distribution and contact forces. Methods: We morphed the PIPER Child model into a male adult-sized model with the help of different target sources including his body surface scans, and spinal and pelvic bone surfaces and an open sourced full body skeleton. We also introduced soft tissue sliding under the ischial tuberosities (ITs). The initial model was adapted for seating applications with low modulus soft tissue material property and mesh refinements for buttock regions, etc. We compared the contact forces and pressure-related parameters simulated using the adult HBM with those obtained experimentally from the person whose data was used for the model development. Four seat configurations, with the seat pan angle varying from 0° to 15° and seat-to-back angle fixed at 100°, were tested. Results: The adult HBM could correctly simulate the contact forces on the backrest, seat pan, and foot support with an average error of less than 22.3 N and 15.5 N in the horizontal and vertical directions, which is small considering the body weight (785 N). In terms of contact area, peak, and mean pressure, the simulation matched well with the experiment for the seat pan. With soft tissue sliding, higher soft tissue compression was obtained in agreement with the observations from recent MRI studies. Discussion: The present adult model could be used as a reference using a morphing tool as proposed in PIPER. The model will be published openly online as part of the PIPER open-source project (www.PIPER-project.org) to facilitate its reuse and improvement as well as its specific adaptation for different applications.

The design of a family of parametric anatomically-based compliant buttock models to evaluate wheelchair cushion performance

The evaluation of wheelchair cushion performance is of interest to a variety of stakeholders, including standards organizations, cushion manufacturers, clinicians, users and payers. The objective of this project was to develop a family of compliant buttock models that are based upon the anatomical parameters of persons with varying body sizes. The models are parametrically designed so can be scaled to evaluate different sized cushions. This paper will detail the designs, describe the anatomical basis for the design and provide the rationale for the design decisions. The manuscript also serves a secondary purpose to illustrate how anthropometric data can be applied to the design of anatomical phantoms that reflect both soft tissue and skeletal anthropometry. Supplemental material includes greater detail and the full CAD files and model fabrication instructions are available in an open access repository for persons who wish to fabricate the models.

Subcutaneous Fat Thickness Remarkably Influences Contact Pressure and Load Distribution of Buttock in Seated Posture

Spinal cord injury patients are prone to develop deep tissue injury (DTI) as they may spend half their time per day in sitting postures, which produce excessive load in their buttocks. However, the impact of fat thickness on the biomechanical response of buttock in sitting posture remained unclear. This study aimed to investigate the influence of subcutaneous fat thickness on the interface pressure and load distribution of buttock of seated humans. To achieve this goal, a 3-dimensional finite element model of male buttock was constructed and the contact pressure on a rigid cushion was evaluated against experimental results. The modified models, which had various fat thicknesses under ischial tuberosity, were built and used to simulate the sitting conditions with different cushion stiffnesses. In the models simulating sitting on the rigid cushion, the peak contact pressure ranges from 0.052 MPa to 0.149 MPa. In the simulation of sitting on the soft cushion, the peak stress of muscle underneath ischial tuberosity in the model with the thickest fat tissue was slightly higher than that of the other models. The results demonstrate that the fat tissue in the buttock could reduce the contact pressure when sitting on the rigid seat. However, contact pressure solely could not be used to estimate the internal tissue stress of seated buttock, especially in subjects with thicker fat tissue.

Volumetric Evaluation of Dead Space in Ischial Pressure Injuries Using Magnetic Resonance Imaging: A Case Series

OBJECTIVE

To establish a preoperative evaluation procedure by measuring the volume of dead space using MRI in patients with ischial pressure injuries.

METHODS

Patients with spinal cord injury and ischial pressure injuries who underwent treatment between August 2016 and November 2019 were included in the study. Preoperative MRI scan was conducted on all patients. The volume estimation and three-dimensional (3D) reconstruction were performed based on MRI data using a 3D Slicer. Based on the resulting volume, a muscle flap that could fit the dead space was selected. Surgery was performed with the selected muscle flap, and a fasciocutaneous flap was added, if necessary.

RESULTS

A total of eight patients with ischial pressure injuries were included in the study. The mean patient age was 59.0 ± 11.0 years. The mean body mass index was 26.62 ± 3.89 kg/m2. The mean volume of dead space was 104.75 ± 81.05 cm3. The gracilis muscle was the most selected muscle flap and was used in four patients. In five of eight cases, a fasciocutaneous flap was used as well. The mean follow-up period was 16 months, and by that point, none of the patients evinced complications that required surgery.

CONCLUSIONS

To the authors' knowledge, this is the first report on volumetric evaluation of dead space in ischial pressure injuries. The authors believe that the 3D reconstruction process would enable adequate dead space obliteration in ischial pressure injuries. The authors propose that preoperative MRI scans in patients with ischial pressure injury should become an essential part of the process.

Changes in external ischial tuberosity width at varying trunk-thigh angles between sexes using two measurement methods

This study examined the influence of two methods and various trunk–thigh (TT) angles on external ischial tuberosity width (EITW) for 45 men and 45 women. In the experiment, the impress and seat pressure methods were applied at TT angles of 60°, 75°, 90°, and 105°. When the impress method was used, EITW remained highly consistent across the four measured TT angles with differences of 2.8 and 2.1 mm for men and women, respectively. Conversely, in the seated pressure method, EITW increased with TT angle such that differences in EITW across a full TT angle range were 11.5 and 11.7 mm for men and women, respectively. Irrespective of method, differences in EITW between genders measured approximately 12.6–13.7 mm across all TT angles. Correlation analyses revealed that hip circumference was positively related to EITW in all cases, whereas the relationship of hip width and depth with EITW varied by method and gender. Because of inherent differences in EITW between genders, these findings suggest that gender variability should be considered in seat cushion design.

Comparison of interface pressures in two dynamic pressure ulcer prevention supports (NIMBUS 3 and SUMMIT): A randomized controlled trial

BACKGROUND

Pressure ulcers are a risk for bedridden patients and various supports exist to prevent them. The Pressure Relief Index (PRI) evaluates pressure relief of dynamic mattresses over time. This study compared the PRI of the SUMMIT mattress (AKS-France) and the NIMBUS 3 (HNE Medical).

METHODS

In this non-blinded, randomized, crossover, non-inferiority study, patients aged ≥60 with a BMI of 16-35 kg/m2, predominantly confined to bed, able to walk with aid and with pelvic symmetry were recruited from a hospital rehabilitation department from March-April 2012. Exclusion criteria included past or present pressure ulcers, inability to remain supine and deep vein thrombosis. Peak pressures of the sacrum were recorded at 0.1 Hz during a single complete 10-min inflating cycle on both mattresses, with the order determined via electronic randomization allocation.

RESULTS

Thirty-one subjects were included and randomized; with 14 finally analyzed in the SUMMIT-NIBMUS 3 order group and 16 in the NIMBUS 3-SUMMIT group. The difference in PRI <30 mmHg between the two mattresses was 13.2% [0.3-26.1] (p < 0.05), allowing a non-inferiority - superiority switch. The SUMMIT mattress demonstrated a significantly higher percentage of time <30 mmHg (p = 0.0454). No significant difference in mean minimal pressure was seen (p = 0.3231) and mean maximal pressure was in favor of SUMMIT mattress (p = 0.0096). BMI did not affect pressure profile. There were no adverse events.

CONCLUSIONS

Evaluated by the PRI, the SUMMIT mattress had a better interface pressure profile than the NIMBUS 3 in older patients. The PRI is a promising tool for clinical decision-making and research, warranting validation.

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

BACKGROUND

Factors 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.

OBJECTIVE

To 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.

RESULTS

A 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.

CONCLUSION

Seat 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.

A Case Study on the Effects of Foam and Seat Pan Inclination on the Deformation of Seated Buttocks Using MRI

OCCUPATIONAL APPLICATIONSWe investigated the effects of seat pan inclination and foam on the deformation of the seated buttocks using an upright MRI system. From observations among four healthy males, we found that soft tissue deformation under the ischial tuberosity (IT) could be reduced not only by using a soft cushion, but also by decreasing the shear force on the seat pan surface. These results suggest that soft tissue deformation could be used as an objective measure for assessing seating discomfort and injury risk, by accounting for the effects of both contact pressure and shear. We also confirmed that the gluteus maximus (GM) muscle displaced away from the IT once seated. As peak pressure and shear are most likely located below the IT, more realistic computational human body models in this region are needed that consider muscle sliding.

Review of Measuring Microenvironmental Changes at the Body-Seat Interface and the Relationship between Object Measurement and Subjective Evaluation

Being seated has increasingly pervaded both working and leisure lifestyles, with development of more comfortable seating surfaces dependent on feedback from subjective questionnaires and design aesthetics. As a consequence, research has become focused on how to objectively resolve factors that might underpin comfort and discomfort. This review summarizes objective methods of measuring the microenvironmental changes at the body–seat interface and examines the relationship between objective measurement and subjective sensation. From the perspective of physical parameters, pressure detection accounted for nearly two thirds (37/54) of the publications, followed by microclimatic information (temperature and relative humidity: 18/54): it is to be noted that one article included both microclimate and pressure measurements and was placed into both categories. In fact, accumulated temperature and relative humidity at the body–seat interface have similarly negative effects on prolonged sitting to that of unrelieved pressure. Another interesting finding was the correlation between objective measurement and subjective evaluation; however, the validity of this may be called into question because of the differences in experiment design between studies.

A Primary Care Provider's Guide to Wheelchair Prescription for Persons With Spinal Cord Injury

The wheelchair is an essential tool for individuals with spinal cord injury (SCI). When the capacity and fit of a wheelchair is matched to the needs and abilities of an individual with SCI, health, function, community participation, and quality of life are maximized. Throughout an individual's life, function and health status can decline (or improve), necessitating a new wheelchair and/or seating components (eg, cushions and backrests). Additionally, a patient's current wheelchair may be identified as a factor contributing to a health concern or functional deficit, again necessitating wheelchair adjustments. Primary care physicians often manage the complex and lifelong medical needs of individuals with SCI and play a key role in wheelchair evaluation and prescription. This article provides a broad overview of indicators that a new wheelchair is needed, describes the wheelchair prescription process, identifies important team members, reviews the major wheelchair components, and provides guidance to match components to patients' needs and abilities.

Seated buttocks anatomy and its impact on biomechanical risk

AIM

The objective of this study was to describe the amount, types, and shapes of tissue present in the buttocks during sitting (i.e., seated buttocks soft tissue anatomy), and the impact of seated buttocks soft tissue anatomy on biomechanical risk.

MATERIALS AND METHODS

The buttocks of 35 people, including 29 full-time wheelchair users with and without a history of pelvic pressure ulcers were scanned sitting upright on 3" of flat HR45 foam in a FONAR Upright MRI. Multi-planar scans were analyzed to calculate bulk tissue thickness, tissue composition, gluteus maximus coverage at the ischium, the contour of the skin, and pelvic tilt.

RESULTS

Bulk tissue thickness varied from 5.6 to 32.1 mm, was composed mostly of adipose tissue, and was greatest in the able-bodied cohort. Skin contours varied significantly across status group, with wheelchair users with a history of pressure ulcers having tissue with a peaked contour with a radius of curvature of 65.9 mm that wrapped more closely to the ischium (thickness at the apex = 8.2 mm) as compared to wheelchair users with no pressure ulcer history (radius of curvature = 91.5 mm and apex thickness = 14.5 mm). Finally, the majority of participants presented with little to no gluteus coverage over their ischial tuberosity, regardless of status group.

CONCLUSIONS

This study provides quantitative evidence that Biomechanical Risk, or the intrinsic characteristic of an individual's soft tissues to deform in response to extrinsic applied forces, is greater in individuals at greater risk for pressure ulcers.