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Understanding 'Horizontal Stiffness' for Proper Cushion Selection

Kirsten Davin, OTD, OTR/L, ATP, SMS

August 11, 2014

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Question

What does the term ‘horizontal stiffness’ refer to when selecting a cushion for a client’s wheelchair?  Why is it important to consider?

Answer

During cushion selection, the key concept to keep in mind is "horizontal stiffness".  Horizontal stiffness is important to address because it will determine which type of cushion will be the most appropriate for your client.  Horizontal stiffness is essentially defined as how stiff or stable the cushion is in the horizontal plane while sitting on top of it.  For example, if you attempt to wiggle when sitting on top of a hard, wooden surface, it will not move in a lateral direction.  This wooden surface is considered to have a very high degree of horizontal stiffness.  A dense foam cushion would also have a high degree of horizontal stiffness because it will not move much laterally while a person is sitting on it and moving around.  In contrast, the air cushion has a low degree of horizontal stiffness. 

The figure below shows a cushion with a low degree of horizontal stiffness on top and a cushion with a high degree of horizontal stiffness on the bottom.  If you have a cushion with a high degree of horizontal stiffness, the good news is that it will provide a very high degree of stability.  It will give your client a good solid base of support.  However, clients with bony prominences or low body mass indices may slide around on top of cushions with high horizontal stiffness increasing friction and shear forces against their skin.  In contrast, when a client sits on a cushion with a very low degree of horizontal stiffness such as an air cushion, there are less shear and friction forces against the skin.  When the client wiggles around on top of the air cushion, the air that is under her/him will move around as well.  The good news is the risk of skin breakdown due to shear and friction is going to be reduced; however the stability and support will be reduced.  When selecting the best cushion option for your client, it is important to determine how much stability does the client need versus how much are they at risk for skin breakdown due to shear and friction forces?  Fortunately, there are a lot of different types of cushion options available today.  Many will have mixed medium or different layering options where the cushion starts with a very firm base, then a middle layer with less horizontal stiffness and an air bladder or gel inlay under the actual contact area.  The foam base will take care of the stability factor and the gel or air inlay under the actual contact area will take care of the shear risk factor.

Wheelchair cushion comparison for stability and shear for Occupational Therapy

 

Editor’s note: This Ask the Expert was adapted from the article ‘Selecting the Ideal Wheelchair Seating System’.  The complete article can be accessed here.


kirsten davin

Kirsten Davin, OTD, OTR/L, ATP, SMS

Dr. Kirsten Davin is a veteran Occupational Therapist of nearly 20 years, with extensive experience in a variety of practice settings including inpatient rehabilitation, acute care, intensive care, and the Central Illinois Regional Burn Center. Since initially obtaining her bachelor’s in occupational therapy in 2001, followed by her post-professional OT Doctorate (OTD) in 2007, Kirsten has served not only as a clinician but also in the role of a clinical consultant specializing in product design and development. Kirsten has fabricated hundreds of splints within her acute care and clinical consulting career, many of which were custom fabricated and individually designed on a case-by-case basis. Her splinting experience ranges from a standard safe position and resting hand splints to highly intricate dynamic splints for the hand, wrist, lower extremities, and cervical spine, incorporating all varieties of materials and splinting medium.

For more than a decade, she has been best known for her live, national speaking tours, which to date have reached over 20,000 therapists in 46 states.  She has conducted thousands of educational events on the topics of seating/positioning, assistive technology, work-life balance, acute care/ICU rehabilitation, splint fabrication, orthotic application, and more. Dr. Davin is an engaging speaker who strives to make learning fun. 

 


Related Courses

Successful Static Splinting: Foundations, Part 1
Presented by Kirsten Davin, OTD, OTR/L, ATP, SMS
Video

Presenter

Kirsten Davin, OTD, OTR/L, ATP, SMS
Course: #4768Level: Introductory1 Hour
  'This course is a great review'   Read Reviews
Following a brief overview of the history of splint fabrication and the advances in the splinting and orthotics arena, an anatomical review of hand structures and landmarks will be performed. Types of splints as well as the variety in thermoplastic materials and characteristics will be presented in preparation for additional courses within this series. This course is Part 1 of a 4-part series on static splinting.

Successful Static Splinting: Forearm Based Splint Fabrication, Part 2
Presented by Kirsten Davin, OTD, OTR/L, ATP, SMS
Video

Presenter

Kirsten Davin, OTD, OTR/L, ATP, SMS
Course: #4785Level: Intermediate1 Hour
  'Helpful review'   Read Reviews
In this course, types of pre-cut, pre-formed and sheet-based splint fabrication techniques are explored as well as a comparison between volar and dorsal-based approaches. A detailed demonstration of four types of forearm-based wrist orthotics are presented, including radial gutter/thumb spica splints, dorsal and volar wrist cock-ups, and functional position with an intrinsic plus modification option. This course is Part 2 of a 4-part series on static splinting.

Dynamic Splinting: Building the Foundation for Success, Part 1
Presented by Kirsten Davin, OTD, OTR/L, ATP, SMS
Video

Presenter

Kirsten Davin, OTD, OTR/L, ATP, SMS
Course: #5044Level: Intermediate1 Hour
  'great explanations and diagrams'   Read Reviews
Following a brief anatomical review of hand structures in order to ensure understanding of the theory, purpose, and methods behind many dynamic splint designs, Dr. Davin offers a comparison of the qualities of static splinting as compared to dynamic splinting. An overview of various dynamic splinting options is introduced and serves to build foundational knowledge as it relates to dynamic splinting in preparation for upcoming courses within this series.

Dynamic Splinting: Splinting for Wrist Function, Part 2
Presented by Kirsten Davin, OTD, OTR/L, ATP, SMS
Video

Presenter

Kirsten Davin, OTD, OTR/L, ATP, SMS
Course: #5045Level: Intermediate1 Hour
  'Clear explanation, examples of splinting material and process in a real situation'   Read Reviews
This course offers a closer look at the world of dynamic splint fabrication and application via an examination of the methods associated with fabricating and/or implementing dynamic wrist splints to manage a client’s wrist-based range of motion, support, and joint protection needs.

Dynamic Splinting: Splinting for Elbow Function, Part 3
Presented by Kirsten Davin, OTD, OTR/L, ATP, SMS
Video

Presenter

Kirsten Davin, OTD, OTR/L, ATP, SMS
Course: #5066Level: Intermediate1 Hour
  'Instructor was very clear and explained the purpose of splinting well'   Read Reviews
This course reviews the world of dynamic splint fabrication and application via an examination of the methods associated with fabricating and/or implementing dynamic elbow splints to manage a client’s elbow and forearm-based range of motion, support, and joint protection needs. Custom and pre-fabricated designs are discussed and compared.

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