Education in Motion / Clinical Corner / January 2015 / WC20 and Secondary Postural Supports When Traveling in Motor Vehicles

WC20 and Secondary Postural Supports When Traveling in Motor Vehicles

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Last month, we looked at Wheelchair Tiedowns and Occupant Restraint Systems (WTORS) and the previous month, we looked at WC19 – the voluntary standard for wheelchairs used as seats in motor vehicles. Let's continue our look at the factors that enhance safety for individuals who remain seated in their wheelchairs while travelling in motor vehicles. Specifically, we will look at WC20, which is the voluntary standard related to seating devices for use in motor vehicles, and we will look at some of the recommendations from the Guidelines for Use of Secondary Postural Support Devices by Wheelchair Users During Travel in Motor Vehicles.

Wheelchair Seating Systems for Use in Motor Vehicles (WC20)

WC19 is the voluntary standard related to wheelchairs used as seats in motor vehicles. It is recognized that one manufacturer's seating system, however, may be affixed to another manufacturer's mobility base. Thus, when looking at safety for individuals who must remain seated in their wheelchairs, it became apparent that there should be separate testing to evaluate the design and performance of wheelchair seating systems separate from specific wheelchair frames. WC20 is the voluntary standard for wheelchair seating systems used in motor vehicles. Wheelchair seating includes seats and back support with attachment hardware.1

In order to test the crashworthiness of seating and attachment hardware, a surrogate wheelchair base is used. The surrogate wheelchair base, which can withstand repeated 48 kph/20 g crash tests, is able to accommodate various sizes and types of commercial seating.2 In order to test the seating, the seating is attached to the surrogate wheelchair base with its attachment hardware and the wheelchair base is secured to a frontal impact sled with 4-point tiedowns. An anthropomorphic test device, or "crash test dummy", is secured with a 3-point occupant restraint system. The testing is completed to ensure that the crash test dummy remains in a seated posture at the completion of the test and does not "submarine" under the pelvic safety belt. In addition, the attachment hardware must remain attached to the seating system and to the wheelchair2 and no part of the seating system weighing greater than 100 g should break loose3. If a piece broke loose while in a collision, it could become a projectile and injure others in the vehicle.

It is intended that WC20-compliant seating is installed on a WC19-compliant wheelchair base. The base must then be secured to a vehicle with an approved Wheelchair Tiedown and Occupant Restraint System (WTORS). "The combination of these devices is indicated to obtain the best possible performance when in a transit condition."4 (p. 4). (Click here for more information on WC19 and click here for WTORS, respectively.)

Secondary Postural Support Devices

Secondary postural support devices provide postural and positioning support for individuals seated in wheelchairs and can enhance function for individuals by providing postural stability. Such devices include pelvic positioning belts, head supports, anterior supports, and medial or lateral thigh supports. Although there are is no standardized testing for postural supports when used during motor vehicle transit, guidelines on their use during travel in motor vehicles have been developed based on principles of occupant protection and knowledge of biomechanics of injuries.5

In general, consideration should be given to the risks and the benefits of using postural support devices when travelling in a motor vehicle. Some of the concerns include the support device pressing and injuring a body part during a collision or non-collision event; the support device breaking loose and injuring another occupant of the vehicle; and the device interfering with the proper positioning of the occupant restraints. The benefits may include enhancing the fit of the occupant restraint system by providing postural control that limits forward and lateral movement. Ideally, a wheelchair backrest should be reclined no more than 30 degrees from vertical to prevent sliding under the pelvic safety belt, so the use of postural supports may enhance positioning in a relatively upright, seated posture when travelling in a motor vehicle. For some individuals, postural supports help to maintain airways for respiration or help to achieve positioning for other medical needs.5

As outlined in my previous article on WC19, unless postural supports, such as positioning belts and chest harnesses have been labeled as having been crash tested, they do not provide for restraint for an occupant seated in a wheelchair in a vehicle. This does not mean that postural supports cannot be used in conjunction with approved occupant restraint systems. If a pelvic positioning belt is used, the guidelines recommend that the belt be positioned low on the pelvis and at an angle of 45 degrees or greater to the horizontal to maintain the seated posture.5

For medial thigh support (i.e., a pommel) and for anterior trunk support, the guidelines recommend properly positioning the pelvis and restraining forward movement of the pelvis to prevent sliding into the pommel or sliding under the chest harness in the event of a collision.5

Head supports, although not tested for restraint, may provide some protection against whiplash injury in a rear impact when the headrest is positioned as close to the back of the head as possible. The head support should not exceed 2 inches from the back of the head. In addition, the middle of the pad of the head support should align with the top of the ears. Thought should be given to the pad selection to prevent the head from going under or around the head support when the person is jostled while the vehicle is moving.5

The guidelines note that it is preferable not to use a forehead strap while travelling in a motor vehicle. If an anterior head support, such as a forehead strap, must be used during transit, it should automatically release at the lowest force possible that still provides effective postural support.5 The concern with anterior head support is that if the head is secured but the torso moves forward in a frontal crash, the neck will hyperextend causing injury.5 There is also the potential for forehead straps to slip downwards and cause injury while travelling. If a collar is required for head support, the softest collar possible should be used. A hard or stiff collar produces greater neck tension than a soft collar as shown in frontal crash testing with crash test dummies.5

Ideally, hard lap trays should be removed from wheelchairs and secured separately as a hard lap tray may cause injury to the abdomen in the event of a frontal collision. If a hard lap trays is required for postural support during transit, dense padding should be placed between the individual and the tray to prevent injury to the user. In addition, the tray should be firmly attached to the wheelchair to prevent it from breaking free and injuring other occupants in the event of a crash. Other options for upper extremity support during transit, such as arm troughs or dense foam trays, should be considered.5

Summary

WC20 is the voluntary standard for seating to promote improved safety for individuals who must remained seated in wheelchairs while travelling in motor vehicles. WC20-compliant seating is intended to be installed on WC19-compliant wheelchairs, which are secured to a vehicle with approved WTORS. For individuals who require the use of secondary postural supports, the potential benefits and concerns of using various support devices during transit must be weighed to determine what is most appropriate for a particular individual's unique circumstances.

References

  1. RESNA. (n.d.) RENSA's Position on Wheelchairs Used as Seats in Motor Vehicles. Retrieved from http://www.resna.org/
  2. Rehabilitation Engineering Research Center on Wheelchair Transportation Safety. (2008). ANSI/RESNA WC-20 Seated Devices for Use in Motor Vehicles. Retrieved from http://www.rercwts.pitt.edu/
  3. Rehabilitation Engineering Research Center on Wheelchair Transportation Safety. (2008). Wheelchair Transportation Safety Frequently Asked Questions. Retrieved from http://www.rercwts.org/
  4. Sunrise Medical. (2009). WC20: A New Standard for Adaptive Seating Product Design. Retrieved from https://marketing.sunrisemedical.com/
  5. Rehabilitation Engineering Research Center on Wheelchair Transportation Safety. (2006). Guidelines for Use of Secondary Postural Support Devices by Wheelchair Users During Travel in Motor Vehicles. Retrieved from http://www.rercwts.org/

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