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

Akins, Jonathan S (2011) Investigation of Interface Shear Stresses on Wheelchair Seat Cushions and the Effects on Subcutaneous Buttock Soft Tissues. Master's Thesis, University of Pittsburgh. (Unpublished)

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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.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Akins, Jonathan Sjsa14@pitt.eduJSA14
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairBrienza, DavidDBRIENZA@pitt.eduDBRIENZA
Committee MemberRedfern,
Committee MemberKarg, Patriciatkarg@pitt.eduTKARG
Date: 3 August 2011
Date Type: Completion
Defense Date: 7 November 2008
Approval Date: 3 August 2011
Submission Date: 4 December 2008
Access Restriction: 5 year -- Restrict access to University of Pittsburgh for a period of 5 years.
Institution: University of Pittsburgh
Schools and Programs: Swanson School of Engineering > Bioengineering
Degree: MSBeng - Master of Science in Bioengineering
Thesis Type: Master's Thesis
Refereed: Yes
Uncontrolled Keywords: finite element model; Pressure ulcers; shear stress; wheelchair seating
Other ID:, etd-12042008-104055
Date Deposited: 10 Nov 2011 20:08
Last Modified: 15 Nov 2016 13:53


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