Module 10 - Power Mobility

Seating system and power seating functions

Power wheelchairs have a substantial range of seat frame and seating system options. The selection of a standard rehab seating system should be based on a thorough assessment as described in Module 7. 

Power seating systems can incorporate electronics modules and actuators to change the orientation of the seat in space as well as the angles within the system.

It is vital to ensure the client can operate the control device throughout the range of  body position in space and angles, and is able to return to the initial posture after using power seating functions.

Keep the system as minimal or as simple as possible, without compromising the client's priority or key seating and wheeled mobility goals. The more 'adds-ons' to the system, the more client and carer training, operational process, equipment maintenance and repairs are required. Trade-offs must be discussed case by case with the client during the process of prescription.

Power seating functions include:

• Tilt-in-space: the seat plane angle rotates around a pivot point without changing the seat to back angle.  Tilt-in-space angle range from -5 degrees (forward) to 65 degrees (backward).
  • A "weight shift tilt" has a sliding pivot point to move the centre of gravity over the power base during the tilt-in-space function, whereas a "fixed pivot" tilt-in-space seating function needs a longer wheel base to maintain stability.
  • Tilt-in-space is one of the weight shift strategies for pressure management. See Module 8.
  • Tilt-in-space uses gravity to improve posture, vision field, pelvic stability and body positioning. See Module 7.
  • A small degree of tilt-in-space adjustment allows the user to optimise balance and stability such as climbing kerb ramps or a steep descent.
  • Improves access to outdoor terrain and entry to vehicles by having adjustment of the ground to foot support clearance.

• Seat elevation: the seating system can be lowered or raised relative to the floor height to improve transfer, functional reach and social interaction.

• Power recline and leg-rest elevation
  • The power recline and leg-rest elevation system changes the seat to back support angle and the seat to leg rest angles respectively. Thus it is vital that the client has the muscle length and joint flexibility to assume these changes in angles.
  • The power recline and leg elevation mechanisms should pivot as close as possible to the axis of the hip and knee joints to reduce displacement that can cause shear. Anti-shear recline and leg elevation systems are designed to move the support surface with the body in order to reduce shear.
  • Power tilt can also be incorporated with power recline and power leg-rest elevation to further stabilise the pelvis and reduce shear.
  • It is preferable that power recline and leg-rest elevation function, or power tilt with leg-rest elevation, are assessed and prescribed together with a customised or synchronised power seating program for clients with a spinal cord injury. The lack of sensation to provide feedback for posture and pressure, and the client's inability to adjust posture, may increase the risk of sliding and pressure ulcers if recline or leg rest elevation is used solely.
  • The possible applications of power recline and leg-rest elevations, or power tilt with leg-rest elevation, for a client with SCI are:
    • greater pressure distribution through a larger support surface
    • a change in posture for rest, or functional task such as self-catheterisation
    • reduction of attendant care needs 
    • management of orthostatic hypotension
    • pain management
    • oedema management, by elevating legs above the heart
    • possible improvement to respiration for clients who are ventilator-dependent.

Resources

"Power drive wheelchair features", Queensland Spinal Cord Injury Service, 2007, accessed 2008. http://www.health.qld.gov.au/qscis/PDF/Equipment/Powerdrive_Wheelchair_Features.pdf