A REVIEW OF FACTORS, SEATING DESIGN, AND SHAPE CAPTURE METHODS FOR REDUCING PRESSURE INJURY RISK

This dissertation in the form of three papers ready for submission to peer-reviewed journals is submitted toward the requirements of the PhD in Health Related Sciences program at Virginia Commonwealth University. Chapter One provides an introductory overview of the project, including: (a) an overview of pressure injuries, (b) the impact of seating as an intervention, and (c) aims of the three-paper dissertation in addressing various aspects of pressure injury prevention. Each paper is unique and singular in its focus, yet all share the overlying aim of addressing pressure injury risk associated with wheelchair seating. Paper One describes the unique facilitators and barriers associated with pressure injury prevention practices among individuals with upper motor neuron lesions. Paper Two consists of a systematic review of the literature on the comparative effectiveness of various wheelchair seat cushions in reducing pressure injuries. Paper Three presents the results of a pilot study of a unique shape-capture method for custom-fitted wheelchair cushions conducted by the student researcher

The Characterisation and Numerical Modelling of Viscoelastic Polyurethane Foams for Use in Custom Wheelchair Seating

Viscoelastic polyurethane foam is widely used in wheelchair cushions as it offers good pressure relieving capabilities. However, the behaviour of this material is largely un-quantified, by comparison with conventional elastomeric materials.Consequently, in many cases, inadequate cushioning is provided to wheelchairusers with complex seating requirements. This thesis characterises andnumerically models viscoelastic polyurethane foam.Temperature-dependent static compression and simple shear test procedures are conducted on a range of viscoelastic polyurethane foams and selected results are utilised to identify Ogden Hyperfoam material model parameters. Time-dependent creep and stress relaxation test procedures are conducted and test results are used in conjunction with Time-Temperature-Superposition (TTS), William-Landel- Ferry (WLF) and Arrhenius theories to generate long-term predictions of material behaviour. Appropriate spring-dashpot models are utilised to model predicted long-term viscoelastic performance. Thermal conductivity parameters are obtained using Glicksman’s theoretical model. The accuracy of predictions obtained using TTS and WLF theories has been proven. Validation has also been achieved for the temperature-dependent Hyperfoam, long-term viscoelastic and thermal conductivity parameters.The range of fully validated material model parameters were utilised to simulatethe in-service seating behaviour of polyurethane foam. Simulation results wererelatively compared and analysed with respect to relevant pressure ulcer riskfactors. From analyses of the FE simulations, results lend support to findings from clinical trials particularly with respect to the relationship between shear and direct pressure in wheelchair seating. Other FE results disagree with accepted seat prescription timings used in current clinical practises

The Characterisation and Numerical Modelling of Viscoelastic Polyurethane Foams for use in Custom Wheelchair Seating.

Viscoelastic polyurethane foam is widely used in wheelchair cushions as it offers good pressure relieving capabilities. However, the behaviour of this material is largely un-quantified, by comparison with conventional elastomeric materials. Consequently, in many cases, inadequate cushioning is provided to wheelchair users with complex seating requirements. This thesis characterises and numerically models viscoelastic polyurethane foam. Temperature-dependent static compression and simple shear test procedures are conducted on a range of viscoelastic polyurethane foams and selected results are utilised to identify Ogden Hyperfoam material model parameters. Time-dependent creep and stress relaxation test procedures are conducted and test results are used in conjunction with Time-Temperature-Superposition (TTS), William-Landel- Ferry (WLF) and Arrhenius theories to generate long-term predictions of material behaviour. Appropriate spring-dashpot models are utilised to model predicted long-term viscoelastic performance. Thermal conductivity parameters are obtained using Glicksman’s theoretical model. The accuracy of predictions obtained using TTS and WLF theories has been proven. Validation has also been achieved for the temperature-dependent Hyperfoam, long-term viscoelastic and thermal conductivity parameters. The range of fully validated material model parameters were utilised to simulate the in-service seating behaviour of polyurethane foam. Simulation results were relatively compared and analysed with respect to relevant pressure ulcer risk factors. From analyses of the FE simulations, results lend support to findings from clinical trials particularly with respect to the relationship between shear and direct pressure in wheelchair seating. Other FE results disagree with accepted seat prescription timings used in current clinical practises

Republication of Uses of Braces and Orthotics for Conservative Management of Foot and Ankle Disorders .

Nonsurgical management is almost always considered the first-line treatment for the vast majority of foot and ankle pathologies. Foot orthoses, shoe modifications, and therapeutic footwear are considered essential tools for successful conservative management of different foot and ankle disorders. Orthopedic foot and ankle surgeons should have a meticulous understanding of the lower extremity biomechanics as well as the pathoanatomy and the sequelae of diseases affecting the foot and/or ankle. This is essential to the understanding of the desired effects of the different inserts, orthotics, shoe modifications, or braces that may be prescribed for these conditions. In this article, we will summarize the orthoses used for treatment of the most commonly encountered foot and ankle pathologies, with the exclusion of treatment for the diabetic foot because of the unique requirements of that disease process

Investigation of Interface Shear Stresses on Wheelchair Seat Cushions and the Effects on Subcutaneous Buttock Soft Tissues

Pressure ulcer incidence rates have remained constant [1] even though wheelchair seat cushion technologies have advanced. Shear stress is recognized as a risk factor for pressure ulcer development [2] and is a focus of many shear reduction technologies incorporated into cushions; however, shear reduction has not been quantified in the literature. This study evaluated 21 commercial wheelchair seat cushions using a methodology developed to quantify interface shear stress and calculate overall and local horizontal stiffness values. For statistical analyses, the cushions were grouped by Healthcare Common Procedure Coding System (HCPCS) codes. The general use cushion category (E2601) resulted in significantly greater interface shear stresses (p<.001) than all other categories and the adjustable skin protection cushion category (K0734) resulted in significantly less interface shear stress (p<.001) than all other categories. Additionally, this study provided evidence that the current horizontal stiffness test methodology (ISO 16840-2) [3] provides sufficient information to characterize wheelchair seat cushions, but does not directly quantify interface shear stress.Results from the evaluation of commercial wheelchair seat cushions provided evidence of materials and technologies that may reduce the risk of pressure ulcers. Based on these results, three prototype cushions were conceptualized and prototyped into a closed-loop control system. The closed-loop control system monitored interface stress amplitude to actively modulate cushion properties. None of the prototypes effectively reduced interface shear stress using the methodology developed for cushion testing.Subcutaneous buttock soft tissues were investigated using a finite element model. Researchers have previously used finite element models [4-13]; however, this study improved upon image collection methodology and validation techniques. MR images of one subject were collected in three seated postures and were used to create 3-D models of the buttock. A non-linear 3-D finite element model was developed with anatomical geometries using hyperelastic and viscoelastic constitutive models. Interface pressure, interface shear stress, and soft tissue displacements were used to validate the model. A parametric analysis resulted in a partially validated model that provided subcutaneous stresses and strains for the upright seated posture. The validated model will be used in future studies to evaluate the SCI population and to evaluate commercial and prototype wheelchair seat cushions

The Effectiveness and Use of Seat Tilt, Backrest Recline, and Seat Elevation in Adult Powered Wheelchair Users

This study examined how adults use power wheelchair seat features such as seat tilt, backrest recline, and seat elevation, during typical daily activities. A Seat Feature Data Logger (SFDL) was attached to 11 subject's wheelchairs for 10-14 days to gather data regarding daily usage of the wheelchair and these features. Subjects occupied their wheelchairs for 12.0 ± 3.0 hours per day and transferred in/out of their wheelchairs 5.0 ± 5.3 times per day. An average of 0.7 ± 1.5 hours per day was spent in an upright position. The tilt feature was accessed 18.4 ± 14.4 times per day for 8.5 ± 5.2 hours per day, and recline was accessed 11.5 ± 8.4 times per day for 8.6 ± 4.6 hours per day. Tilt and recline were used in combination for a total of 4.8 ± 4.6 hours per day. Subjects accessed the seat elevation feature 4.3 ± 4.1 times per day on average for 2.8 ± 4.6 hours day. Based on these data it was found that subjects spent significantly more time in a tilted versus an upright position (p<0.025), but that tilt was not used significantly more than recline (p=0.155) or seat elevation (p=0.046). In addition, comparison of SFDL data with pressuremapping data revealed that subjects were more likely to use small and intermediate amplitude tilt and recline angles, and positions known to result in low peak pressure were accessed more frequently and for longer durations than intermediate and high pressure positions. While subjects did not always use large angles of tilt and recline - as many clinicians recommend - these features were used frequently and their use resulted in lower peak pressures

A new perspective on the design of pressure relief cushions for those with spinal injuries

The aim of this study is to develop new insights which pressure relief (PR) cushion designers can use to guide the design of new cushions with greater efficacy at preventing pressure ulcers than contemporary cushions. A methodological framework was formulated which incorporated a number of research techniques from the user-centred methodology USERfit, and included methodological triangulation. Exploratory interviews and observational work were conducted in a specialist unit for spinal cord injury (SCI). This involved ten patients, four physiotherapists, two nurses and an outpatient technician. Additionally, two questionnaires were designed and circulated amongst SCI patients and staff with completed responses from 41 patients and 31 staff. From the analyses of the data gathered from the literature, observational work, interviews and questionnaire responses, 28 recommendations for cushion design were formulated. These recommendations covered the principles which underpin cushion design, cushion usability and the future direction of cushion design

An active seating system for prevention of pressure sores

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1997.Includes bibliographical references (leaves 64-65).A pressure management and relief system has been developed for use by wheelchairbound individuals who are at risk of developing pressure sores. This system can be used in passive or active form, depending on an individual's requirement for pressure management and relief. The active seat uses vacuum and pressure in combination with an open-cell-foam-based cushion to perform pressure relief. Testing methods for the system were studied and developed. These methods allow a controlled and precise testing of seating systems. Prototype systems have also been produced and tested. Experimental equipment and data are presented to support performance claims. Prototypes of both active and passive systems have also been tested in a pilot clinical study to assess their effectiveness. Results from this study are presented.by Gustavo Y. Buhacoff.S.M

Factors Associated with Clinical Decisions and Pressure Ulcer Development in Long Term Care Residents

With the growing number of elderly long-term care residents in the United States, pressure ulcers (PU) represent a significant healthcare problem. The National Pressure Ulcer Advisory Panel (NPUAP) reported in 2001 that the incidence rates of PU in long-term care residents ranged from 2.2% to 23.9% and the prevalence from 2.3% to 28%. Multiple risk factors for the development of PU have been suggested, and can be divided into extrinsic factors and intrinsic factors. The aims of this study were to: (1) conduct a focused literature review of intrinsic and extrinsic factors related to PU development in elderly long-term care residents; (2) conduct a secondary analysis of demographic and clinical data from Randomized Clinical Trial on Preventing Pressure Ulcers with Seat Cushions (RCT-SC), to identify risk factors associated with acquiring/not acquiring a PU in elderly long-term care residents. Three different methods were used to analyze the data: (a) stepwise logistic regression, (b) odds ratios, and (c) Exhaustive Chi-Square Automatic Interaction Detection (CHAID); and generate a decision-making tree for the prescription of wheelchairs and seat cushions by rehabilitation practitioners for elderly long-term care wheelchair users. Inter-rater and intra-rater reliability of the rehabilitation team decisions were also established. As a result of this study it was concluded that:(a) the focused literature review provided useful information about intrinsic, extrinsic and combinations of these risk factors in PU acquisition,(b) the stepwise logistic regression, odds ratios, and CHAID analyses confirmed known risk factors and added new risk factors that predict PU development,(c) the decision-making tree can be a starting point for rehabilitation practitioners that are new to the field of seating and mobility, and (d) the decision making tree showed that the use of a pressure mapping system is a good tool if used in combination with clinical judgment