Potential Causes of Sliding for Individuals Who Foot Propel

Learning why a person slides from their wheelchair is the only way to discover the solution to address issues of sliding. For an individual who foot propels or who hand and foot propels, the potential causes of sliding may be related to their positioning in the wheelchair and/or to the set up and maintenance of the manual wheelchair itself. This month's Clinical Corner article will focus on wheelchair set up and maintenance as factors to consider in addressing issues of sliding for those who use one or both feet to move and maneuver a manual wheelchair.

"Quick Fix" Solutions That Are Not Really Solutions

Before we begin to look at the potential causes of sliding in a manual wheelchair, let's first look at what some may reach for to try to prevent sliding. Often the reaction to seeing a client sliding when they are foot propelling is to apply a wedge cushion or a 4-point positioning belt to try to prevent the sliding.

The rationale behind the use of a wedge cushion is that by decreasing the thigh to trunk angle, the pelvis will be held in position at the back of the wheelchair. That is, the pelvis will be "wedged" into position on the wheelchair. Does this work? If a person has insufficient range of motion to tolerate this position, the person will continue to slide into a posterior pelvic tilt to relieve the discomfort caused by squeezing the hips and pelvis into a position that cannot be tolerated. In this case, the wedge cushion will not work to prevent sliding and may cause additional problems, such as shear.

The thought behind the use of a positioning belt is that the belt will secure the pelvis into position to prevent sliding; however, a positioning belt will not work to prevent sliding if the cause of sliding has not been addressed. A person will slide into, or under, a positioning belt and be at risk for injury. The purpose of a positioning belt is to stabilize the pelvis after seating and wheelchair configuration has been optimized for a person's presenting posture. A positioning belt has its place in seating and mobility prescriptions, but not as a means to prevent sliding.

Potential Causes of Sliding When Propelling a Wheelchair by Foot

Improper positioning can contribute to sliding for individuals who use wheelchairs. For the purpose of this month's topic, let's assume that a person is well-positioned in their wheelchair; that is, that the seat to back angle respects the client's tolerated thigh to trunk angle and that the cushion and back support are appropriate for the client's needs. This assumption lets us focus solely on issues that may be related to the wheelchair set up that are contributing factors to sliding.

Some possible causes of sliding for an individual who foot propels or who hand and foot propels are:

Seat to floor height is incorrect for the individual.

If the finished seat to floor height is too high or too low for an individual, they may slide their pelvis forward to assist in obtaining the optimal height for contact between the foot and the floor. When determining the correct height of the finished seat to floor, it is important to take into account the gait pattern the person uses when propelling with the feet. For example, does the person have a shuffling, flat footed gait while sitting in the wheelchair or does the person use a heel strike and pull through pattern? The seat to floor height may be different in each case. Remember to take the measurement in the usual shoes the person wears when foot propelling as the height of a heel can make a difference too!

Rolling resistance of the wheelchair requires too much effort for the individual.

Our high school physics classes taught us about Newton's first law of motion, which states that a body at rest tends to stay at rest, while a body in motion tends to stay in motion, unless acted upon by an external force. When we apply this law of motion to manual wheelchairs, we can think about the forces required to initiate propulsion and the forces that allow the wheelchair to coast with minimal effort.

Inertia, the tendency of an object to resist change in its motion,¹ must be overcome in order to initiate propulsion or movement in a manual wheelchair. Greater force must be used in order to begin propulsion from a stopped position compared to maintaining a constant self-selected pace.² In order to maintain a constant speed over a level surface, a person using a wheelchair must overcome rolling resistance.³ Rolling resistance is defined as the force that resists the motion when an object rolls on a surface.⁴ Rolling resistance will limit the distance a manual wheelchair coasts after a force, such as from a push stroke or lower extremity movement, is applied.

Several factors contribute to rolling resistance in a manual wheelchair. These factors include:

• mass of the user and the mass of the system
• weight distribution between the front casters and the rear wheels
• size and type of casters and tires selected
• surface on which the wheelchair rolls³.

So what does all of this mean for someone who foot propels or hand and foot propels? To initiate propulsion, the individual must overcome the inherent inertia of the wheelchair. It takes more effort to start the movement of the wheelchair than it does to maintain the movement of the wheelchair. If the wheelchair is not optimally set up for the individual who foot propels, it takes more effort to initiate and then to maintain propulsion. The individual must apply greater force through the lower leg when making contact between the foot and the floor. Rather than the wheelchair rolling smoothly, the force through the lower extremities is transferred up the body, pulling the pelvis forward and causing the individual to slide in the wheelchair. Minimalizing the rolling resistance through optimal set up can help to prevent sliding for an individual who foot propels or who hand and foot propels.

Wheelchair requires maintenance.

There are some maintenance issues that will cause a manual wheelchair to require more effort to move. Issues such as caster flutter, pneumatic tire inflation, toe on the rear wheels, and debris around the axle of the casters or rear wheels limiting their rotation will contribute to the increased effort required to initiate or maintain movement of the wheelchair. Again, if the individual must apply more force through the lower extremities when making contact with the ground in an effort to move the wheelchair, the pelvis may be pulled forward, causing sliding for the individual. Maintaining a manual wheelchair can help to minimize the risk of sliding for an individual who foot propels or who hand and foot propels.

It is only by finding the true cause of sliding from a wheelchair that the proper solution can be found. "Quick fixes" tend not to work effectively and may lead to other problems. There may be multiple reasons why an individual who uses one or both lower extremities to propel a wheelchair may slide from the wheelchair. A thorough assessment of the cause of sliding is required in order to find the solution that is appropriate for each unique individual.

Please send your comments, questions, and suggestions for Clinical Corner topics to Sheilagh Sherman, OT Reg. (Ont.) at Sheilagh.Sherman@sunmed.com. Thank you!

References

1. Caspall, J.J., Seligsohn, E., Dao, P.V., & Sprigle, S. (2013). Changes in inertia and effect on turning effort across different wheelchair configurations.Journal of Rehabilitation Research & Development. 50(10), 1353-1362.
2. Koontz, A.M., Cooper, R.A., Boninger, M.L., Yang, Y., Impink, B.G., & van der Woude, L.H.V. (2005). A kinetic analysis of manual wheelchair propulsion during start-up on select indoor and outdoor surfaces. Journal of Rehabilitation Research & Development. 42(4), 447-458.
3. Tomlinson, J.D. (2000). Managing maneuverability and rear stability of adjustable manual wheelchairs: An update. Physical Therapy, 80(9), 904-911.
4. Wikipedia. (2014). Rolling resistance. Retrieved from https://en.wikipedia.org/wiki/Rolling_resistance.

Note: The content of this article is not meant to be prescriptive; rather, it is meant as a general resource for clinicians to then use clinical reasoning skills to determine optimal solutions for individual clients. Sheilagh is unable to answer questions from members of the general public. Members of the general public are directed to their own therapists or other health care professionals to ask questions regarding needs.

This article is © Sunrise Medical, Inc., 2021 and cannot be copied, distributed, or otherwise reproduced in whole or in part without the express written permission of Sunrise Medical Canada.