Cushions

Introduction

All wheelchair users should be comfortable in their wheelchair, and a good cushion helps them to sit upright easily and comfortably. That is why every wheelchair user should have a cushion. A cushion is a very important part of every wheelchair. [1][2]

Cushions Provide:

  • Comfort;
  • Posture Support; Assists people to sit more upright, where possible in a neutral posture;
  • Pressure Relief.

For many users, a cushion that provides some comfort will help them to use the wheelchair for a longer time. It is not necessary for every wheelchair user to have a pressure relief cushion, but users with limited or no skin sensation are always at risk of developing pressure sores when using a wheelchair without a proper cushion. These users must use a pressure relief cushion to help reduce this risk. An inadequate pressure-relief cushion is the one component of a wheelchair that is most likely to cause pressure sores, serious injury or premature death for those who are high risk for developing pressure areas. [1][2]

Many users require some adaptations or modifications to their cushion to help provide additional postural support or pressure relief. Wheelchair manufacturers need to either keep a good stock of different types and sizes of cushion or have the capacity to produce and modify a cushion as and when needed. Recommendations for cushions are given in Fig.1. [1]

Fig.1 Guidelines for Cushions

Classification of Cushions

There are a range of classification systems developed to describe cushions, the best-known is the classification by user need developed by David Hobson. Although not as well known, the other methods of classification provide useful information in relation to construction materials, different functions of the cushions and their ability to prevent pressure sores. [3]

Classification by User Need

This classification was proposed by David A. Hobson, at the University of Pittsburgh Rehabilitation Engineering Center in the United States [Smith and Leslie, 1990]. It divides PSDs into three categories, which are defined mainly on the basis of the needs of the different user populations, namely, those designed to:

  1. Provide Postural Support and Compensate for Deformations (Individuals with Cerebral Motor Impairment).
  2. Balance Pressure and Maintain Posture (Individuals with Spinal Cord Impairment e.g. Spina Bifida, Spinal Cord Injury).
  3. Improve Comfort and Posture (Individuals with Multiple Impairments and the Older Person).

Classification by Function

Staarink developed a function-based classification of seat and back cushion parameters. [4]

These functions consider;

  1. Seated Position; Quality of Pressure Distribution, Suppleness of the Surface, etc;
  2. Moisture and Heat; Moisture and Heat Control Properties;
  3. Action of Sitting In and Getting Out of the Wheelchair; Indentation in the Sacral, Frontal and Lateral Regions, Friction, Puckering, etc;
  4. Transport (weight, size, portability, etc.).
  5. Maintenance; Textile Cover Washability, Nontextile Cover Cleanability, Odor Resistance, etc;
  6. Durability; The Cover and Cushion, Wear Resistance;
  7. Reliability; Fill-ratio Sensitivity, Sensitivity to Positioning, etc;
  8. Safety and Fire Resistance.

Classification by Construction Material

Most often, seat and back cushions are classified according to their shape and constituent material. From the standpoint of materials, cushions can be divided into three categories:

  1. Foam Cushions;
  2. Fluid-filled Cushions (Air, Water, Elastomer Gels and Viscous Liquids);
  3. Hybrid Models,

These cushions can be static or dynamic. Fluid-filled and foam cushions are static devices designed to even out or distribute pressure on the pelvic contact surface. Dynamic cushion models are based on the principle that high local pressure can be tolerated as long as the duration of contact does not exceed certain pre-established limits. A few applications of this principal have been attempted. For example, there is, in essence, a mechanical model and a model consisting of bellows-type air cells. [2]

Types of Cushion

Cushions can be described in different ways, including:

  • the material they are made from e.g. foam;
  • the material they are filled with e.g. air, fluid or gel;
  • their main function e.g. pressure relief, comfort, posture support;
  • their shape e.g. flat or contoured;
  • how they are made e.g. foam cushions may be “moulded” from one piece of foam or “layered” made from a number of layers of foam).

The most commonly available cushion is a foam cushion. Foam cushions are also usually the least expensive. They are easy to make where foam is available and easy to modify to suit individual wheelchair users.

A pressure relief cushion will help to reduce pressure. Anyone at risk of developing a pressure sore should be given a pressure relief cushion. There are different types of pressure relief cushions. Pressure relief cushions help to reduce pressure by:

  • Distributing a wheelchair user’s weight as evenly as possible across the seat surface;
  • Reducing pressure under high-pressure risk areas e.g. seat bones, hip bones, coccyx/tail bone;
  • Reducing shear by assisting the wheelchair user to sit upright.

Foam Contoured Pressure Relief Cushions

The key features of a foam pressure relief cushion are the following:

Base Layer

The base of a pressure relief cushion should provide a Firm Stable Base. This will ensure the cushion provides good support for the user and does not move when the user moves.

Top Layer

Over the base layer there should be a “comfort layer”. This is a layer (or more than one layer) of softer foam. The top layer should be soft enough to allow the seat bones to sink into it, but should not be so soft that the seat bones can sink all the way to the bottom and rest on the solid base or seat of the wheelchair.

Foam Pressure Relief Cushions vary. Shaping that you may see on a pressure relief cushion includes:

  • A “well” under the seat bones to reduce pressure;
  • Support under the hip bones to help distribute weight;
  • A shelf in front of the seat bones to keep the pelvis more upright and prevent sliding forward;
  • Grooves or gutters for the legs.

Air/Fluid/Gel Pressure Relief Cushions

The key features of a air/fluid/gel pressure relief cushion are the following:

  1. Flotation cushions include those filled with air and those that have a fluid or gel pack;
  2. Gel-pack cushions should have a firm foam base very similar to a foam contoured cushion;
    • Over the Base Layer there is a Gel / Fluid pack;
    • The Gel / Fluid pack automatically matches the shape of the wheelchair user’s body.
    • This helps to distribute the user’s weight evenly and reduces pressure under bony areas.

Which Cushion to Use?

There are advantages and disadvantages of both foam contoured cushions and air/fluid/gel cushions. [2]

Advantages Disadvantages
Foam

Contoured

Cushion

  • Can be made locally (where there is high-quality foam).
  • Can be modified locally to accommodate different needs.
  • Not subject to”sudden collapse” e.g. a puncture in the air/fluid/gel cushions can cause the release of the materials from the cushion and stop the cushion from relieving pressure, causing “sudden collapse” of the cushion.
  • The top layer of a layered foam cushion can be replaced easily and at a low cost, rather than replacing the whole cushion.
  • Foam compresses, becoming flatter and firmer over time. For this reason, foam cushions should be checked regularly and replaced every 1 - 2 years.
  • Can take a while to dry out, a problem for people who are incontinent.
  • Foam insulates and can cause an increase in tissue temperature.
Air / Fluid / Gel

Cushions

  • Pressure is distributed evenly over the seat surface.
  • The gel pad automatically adapts to the body when the wheelchair user moves or changes position.
  • Air/fluid/gel cushions are often more expensive and less readily available than foam cushions.
  • Some wheelchair users find air / fluid / gel filled cushions make them feel unstable.
  • Subject to “sudden collapse”. In any context where a wheelchair user is not able to get a replacement cushion quickly, this can be a problem.

Cushion Covers

A pressure relief cushion should have a cover which can be removed for washing and is water-resistant. The material used for a pressure relief cushion cover should be either stretchy or loose enough to allow the seat bones to sink into the foam. if the cover fabric is not stretchy, a thin fabric is best. Folds in a thin fabric will be less likely to mark the skin and cause a pressure sore. if thin plastic is used under a fabric cover, this also needs to be loose enough to allow the seat bones to sink into the foam.

Always advise wheelchair users that if their cushion or cushion cover becomes wet it needs to be dried and replaced only when dry. For wheelchair users who are incontinent and at risk of developing a pressure sore, provide two cushions which may be used in turn.

Wherever possible, wheelchair users who are incontinent need a cushion cover which is water-resistant and will keep fluid away from the user’s skin.

If there is no water-resistant cover:

  • investigate what assistance can be provided to reduce incontinence;
  • provide a second cushion, so that one can be drying while the user sits on the other;
  • protect the cushion with a very thin plastic bag inside the cover.

If using a plastic bag:

  • check that the plastic bag does not cause the user to “slide” on the cushion;
  • make sure that there are no creases in the plastic bag that could cause a pressure sore;
  • the wheelchair user must ensure that fluid does not “pool” over the plastic, as this increases the risk of a pressure sore;
  • the wheelchair user should ensure that the cover is dried out if it becomes wet and the plastic bag cleaned or replaced.

Testing Pressure

Whenever you prescribe a pressure relief cushion, carry out this simple manual test to check whether the cushion is reducing pressure under the user’s seat bones. The test requires personnel to place their hands underneath the wheelchair user’s seat bones. Always explain to the wheelchair user what you are going to do and why it is important. Always carry out the test with the same cushion and the wheelchair that has been provided for the user.

Manual Pressure Test.jpeg

If Level 2 (Warning) or Level 3 (Unsafe) pressures are found under the sitting bones (Ischial Tuberosities), action is needed to reduce the pressure. A simple solution is to add an extra layer of firm foam. This is called a ”lift”. The lift should be approximately 20 mm thick and have holes cut out under the seat bone area. The lift is placed underneath the cushion and inside the cover. Sometimes more than one layer is needed. Personnel should add one layer and test the pressure. If the pressure is still level 2 or 3, add another layer.

Cushion Fabrication

If foam is available, wheelchair service personnel can make a foam pressure relief cushion with just a few tools. Personnel need to know what foam to use, and a few important dimensions. The instructions below show how to make a basic foam pressure relief cushion, with two key contours. These are a “well” under the seat bones and a shelf in front of the seat bones.[2]

Cushion Features and Dimensions

The main features of the basic foam contoured cushion are the following: [2]

Base Layer (Fig.3)

Made with a firm foam e.g.“chip” foam

Top Layer (Fig.4)

Made with a soft “comfort” foam

Fig. 3 Base Layer
Fig.4 Top Layer

How to Make a Pressure Relief Cushion Base

The following instructions provide a cushion of dimensions 400 mm wide x 400 mm deep x 50 mm high. The Ischial Tuberosity Well is 200 mm wide x 200 mm deep x 35 mm high. This cushion would be suitable for a wheelchair user with a seat width of 400 mm. Adapt the dimensions to suit the size of each wheelchair user as described in the box below.

Mark Out the Cut Lines on the Firm Foam: (Fig.5)

  • Start with a piece of firm foam 400 mm x 400 mm x 50 mm;
  • The centre of the seat bones well must be on the centre line of the cushion;
  • For this size cushion, the Ischial Tuberosity Well should measure 200 mm x 200 mm x 35 mm;
  • Draw the cut lines with a dark coloured marker on all six sides of the base foam.
Fig.5 Line Cut Outs

Dimensions of Seat Bones Well (Fig.6)

Adjust the dimensions of the cushion and the seat bones well to suit individual wheelchair users as follows:

  • Seat Bones Well Width = ½ the wheelchair user’s seat width or 200 mm (whichever is less) [a];
  • Seat Bones Well Depth (front to back) = ½ the wheelchair user’s seat width or 200 mm (whichever is less) [b];
  • Seat Bones Well Height = 35 mm for adults and 20–25 mm for children [c].
Fig. 6 Seat Bones Well Dimensions

Cut Out Seat Bones Well

Use a sharpened hacksaw blade or long knife. Use long slow strokes, cutting mostly when pulling to improve control.

  • First cut through the back of the cushion to the depth of the seat bones well. (Fig.7)
  • Then slice out the seat bones well. (Fig.8)
  • Glue back into place the two “flaps” left on either side of the seat bones well. Allow the glue to set until not completely dried and slightly sticky to touch. Then press the foam together. (Fig.8)
  • Cut off (bevel) the corners inside the seat bones well. (Fig.10)
  • For a slung seat cushion: make an angled cut/bevel on both sides of the base/underside. (Fig.11)
Fig.7
Fig.8
Fig.9
Fig.10
Fig.11

Place the Top Foam Layer on Top of the Cushion

  • Both the base and top layer are placed in the cushion cover together.
  • The two layers do not need to be glued together.
  • If the top layer becomes soiled or worn, it can be washed and dried, or replaced.
  • A lift can be added within the cover to increase the depth of the seat bones well.

Checking Cushion Fit

Always check that the seat bones sit just within the seat bone well and not on the edge or on the high part of the cushion. Always check when fitting a pressure relief cushion for a wheelchair user that:

  • the pressure under the seat bones is “safe” and
  • the seat bones are sitting inside the seat bone well and not on the edge or top layer.

Frequently Asked Questions

How do you decide which fabric to use for the cushion cover?

  • Choose a fabric which is stretchy if possible. Water-resistant fabric is very good if available. if the fabric is water-resistant make sure it is not too thick, or the folds may cause marking on the wheelchair user’s skin, which can lead to a pressure sore.
  • The choice will depend on the fabric available. sometimes the choice is limited.
  • If there is a choice and you are not sure, ask wheelchair users to trial different options.
  • Wheelchair service personnel will develop experience as different fabrics are tried.

Does foam contoured pressure relief cushion work for all users?

  • No, foam contoured pressure relief cushion will not work for all wheelchair users.
  • However, one advantage of this cushion is that it can be easily adapted.

Is the foam contoured pressure relief cushion hot or does it cause sweating?

  • Foam cushions can be hot and can cause sweating.
  • However, the cushion performs well in many other ways, so putting up with the heat is a compromise in some cases.

Do all wheelchair users need a pressure relief cushion?

  • No - not all wheelchair users need a pressure relief cushion.
  • Consider the pressure risk factors to decide whether a wheelchair user is at risk of developing a pressure sore.
  • Although the foam contoured pressure relief cushion may not be needed for pressure relief, the cushion can also improve comfort and posture, even for wheelchair users who are not at risk of developing pressure sores.

What happens if the cushion is used back-to-front or upside down?

  • It will not work properly and may even increase the risk of developing pressure sores.
  • Always make sure that wheelchair users, and family members (where relevant), understand how to use and care for the cushion correctly.
  • Mark the cushion “Front” and “Back” or “Up” and “Down” if necessary.

Does this cushion work for children?

  • Yes, this cushion would work for children. However, the seat bone well needs to be smaller.
  • Many children who use wheelchairs need additional postural support. This cushion may not provide enough postural support

References

  1. 1.0 1.1 1.2 William Armstrong, Johan Borg, Marc Krizack, Alida Lindsley, Kylie Mines, Jon Pearlman, Kim Reisinger, Sarah Sheldon. Guidelines on the Provision of Manual Wheelchairs in Less Resourced Settings. World Health Organization; Geneva: 2008. 
  2. 2.0 2.1 2.2 2.3 2.4 2.5 Sarah Frost, Kylie Mines, Jamie Noon, Elsje Scheffler, and Rebecca Jackson Stoeckle. Wheelchair Service Training Package - Reference Manual for Participants - Basic Level. Section A. Core Knowledge.World Health Organization, Geneva. 2012
  3. Agence d’évaluation des technologies et des modes d’intervention en santé (AETMIS). Postural-support devices. Report prepared by François Pierre Dussault. (AETMIS 03-07). Montréal: AETMIS, 2005, x-47 p.
  4. Staarink HA. Sitting Posture, Comfort and Pressure: Assessing the Quality of Wheelchair Cushions. 1995https://repository.tudelft.nl/islandora/object/uuid:c71e326e-f0a6-47d7-a641-6fe41e82c6c7/
  5. Assistive Technology for All. WSTP Basic Video Series: 9. Pressure Test Demonstration. Available from: https://youtu.be/mswAXgsshc4[last accessed 30/10/17]