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State Spinal Cord Injury Service

Spinal Seating Modules

Wheelchair configuration for the client’s physical attributes and functionality

Wheelchair configuration for the client’s physical attributes and functionality

A wheelchair configuration is based on a summary of findings from the assessment process to set appropriate manual wheelchair prescription goals. Each wheelchair should be configured to meet individual needs for postural support, comfort, transfer technique, functionality and to optimise propulsion efficiency, taking into consideration the individual’s body ‘size’ and ‘shape’.

One of the most challenging aspects of manual wheelchair prescription is that, in general, the wheelchair seat frame shape and dimensions cannot be altered once provided. The frame itself is part of the postural support that needs to be appropriate for the client’s body size and shape. Adjustable components have only limited scope for fine tuning of postural support and propulsion efficiency.

Critical decisions in MWC prescription

1. Seat width
    Seat width
  • Choosing a narrow seat width results in a narrow chair   which improves environmental access. A narrow chair minimises shoulder   abduction and internal rotation during wheelchair propulsion
  • Measure hip width to select seat width; the minimal seat   width must be greater than the distance between the greater trochanters, and
  • The seat width may be influenced by the choice of seat   cushion, or if a rigid backrest is chosen.
2.  ‘Seat depth’, ‘effective seat depth’ and ‘seat frame depth’

Seat depth

Seat depth: depth of seat support surface (e.g. sling).

Effective seat depth: measured from front of seat support surface (e.g. sling) to the centreline of the front of the back rest.

Seat frame depth: A measure of the chair frame more than the seat size. Exact measurement depends on chair manufacturer, check instructions on scripting form.

  • Seat depth selection is not the same as thigh depth as it is influenced by the selection of back support. The way the front of the frame is designed and measured differs between various manufacturers.
  • Seat depth is usually referred to, as the front of back post to the front of seat upholstery or the front edge of the seat rail. Seat frame depth is considered as the measurement of the seat rail from the front of the back post to the start of the bend for the legrest hanger in fixed front frame manual wheelchairs.
  • Check the influence of back support such as sagging back upholstery which will place sacrum rearward while a rigid backrest which may shift sacrum rearward or forward and changes the effective seat depth.
  • Frame depth can vary between manufacturers for their MWC designs, i.e. the frame seat rail may extend forward after the seat upholstery edge by 0.5” to 3”. There are also frame options for frame style which give options for frame depth,  or  custom made frame depth  (E.g. seat depth at 16” with 18” seat frame depth)
  • A swing away legrest assembly usually increases the seat frame depth.
  • For these reasons, a specification of ‘seat depth’ from one wheelchair cannot be directly translated to another without re-measurement and trial. Take note of the instructions in the manufacturer’s order form.
  • Other functional considerations: clients may prefer a 2”-4” shorter seat depth to their popliteal fossa if the lower legs were tucked under to clear the calf bulk, or needs to hook the wrist under the knee to lift the leg up for transfer.
  • The selection seat frame depth may influence the forward / rearward location of front caster. If the frame length is too short, the client’s weight would be distributed over the front castors and the wheelchair is prone to pitch forward.
3. Seat to floor height
  • The height of the client’s seat from the floor affects access to environments such as kitchen, workstation and dining table. Also particularly for those using slide boards, consider the height of transfer surfaces such as the bed and vehicle during assessment.
    • Front seat-to-floor height
  • There should be a minimum of 50mm / 2 inches footplate clearance from the ground.
  • Remember that the cushion will add sitting height, so where possible, the relevant cushion should be used during wheelchair scripting trials.
  • For a client with a 90° thigh-to-lower leg angle, the front seat to floor height is estimated as: ground to footplate clearance + lower leg length + shoes / heel height – estimated cushion height.

    Reduce this dimension for a ‘forward’ or ‘tucked under’ foot placement as the feet are at a further distance from floor (around 25mm /1 inch for a 70° front frame angle or thigh to knee angle). ‘Tucking under’ is a strategy that tall clients use to keep the chair low and short.
    • Rear seat-to-floor height

Selection of rear seat-to-floor height (in relation to the front seat-to-floor height) determines the seat tilt (‘rake’).

Factors determining rear seat-to-floor height are:

  • Biomechanics of propulsion, where upper arm to forearm angle is 100-120°.
  • Functional criteria: e.g. client’s priorities may include being able to overcome seat tilt to slide forward for transfer and self-catheterisation, and having the thighs at a level position to carry items on a tray without sliding off. This may relate to the type of cushion chosen.
  • Stability and posture: A change in seat tilt can be important in postural intervention to reduce the client’s tendency to slide forwards on the seat, or to accommodate a restricted range in thigh-to-trunk angle.
4. Front frame angle / lower leg support angle (measured hanger against horizontal/level floor)

Front frame angle / lower leg support angle

  • Manufacturers provide options of front frame angle in their configurations. A 60° frame angle places the feet more forward than an 80° angle.
  • The way the feet are placed on the footplate will influence the decision for frame angle and footplate angle. Clients with a plantar-flexion contracture in the ankles may need a lesser frame angle to accommodate this so that the feet will not slide off the footplate. Clients with good ROM in the knees and ankles can use a larger frame angle to enable the lower legs to ‘tuck under’, providing a shorter chair with better manoeuvrability in tight spaces.
  • Trials of access to tight spaces, such as car transfer and toilet areas are essential in determining front frame angle.
  • Increasing rear wheel camber will also increase the overall width of the chair (approximately 25mm per 2°)
  • On many chairs the rear wheels can be adjusted closer to or further from the seat by adjusting the axle receivers
  • Some handrims can be set closer or further from the wheel (close tab/far tab)
5. Overall width
  • Increasing rear wheel camber will also increase the overall width of the chair (approximately 25mm per 2°)
  • On many chairs the rear wheels can be adjusted closer to or further from the seat by adjusting the axle receivers
  • Some handrims can be set closer or further from the wheel (close tab/far tab)
6. Other measurement and options

Read the manufacturer’s measuring and scripting instructions carefully as they vary between manufacturers and wheelchair frame styles. Understand the manufacturer’s prescription form to be sure that appropriate accessories and custom options are chosen. Contact the suppliers for support.

References

  1. McKeogh, D.M., 2007. The anatomy of a manual wheelchair [Internet]. Sacramento; 2007 [Oct 2015]. Available from: http://www.csus.edu/indiv/m/mckeoughd/WC%20Anatomy/wcAnat%20wo%20animation.ppt
  2. Babinec, M. Translating Evaluation Measurements to Wheelchair Dimensions [Internet]. Invacare; no date. [cited Oct 2015]. Available from: http://www.invacare.com.au/index.cfm/3,168,522/measurements-to-wc-geometries.pdf
  3. Queensland Spinal Cord Injuries Service. Manual wheelchair: information resource for service providers [Internet]. Queensland Spinal Cord Injuries Service; 2013 [cited Oct 2015]. Available from: https://www.health.qld.gov.au/qscis/documents/manual-wheelchairs.pdf