Prevention of Sliding in Seated Mobility, Part 2

Hello all!

Last month, I wrote about the effects of sliding and the common "quick fixes" and why they tend to not work effectively. This month, I would like to review some of the common equipment and musculo-skeletal factors that influence the potential for sliding as it is only by understanding the causes of sliding that we can find the true solutions. Next month, I will discuss features of generic seating and wheelchair configuration that may assist in preventing sliding.

Sometimes, the reason a person slides in their wheelchair relates to equipment factors. Such factors include: a person being improperly positioned in the wheelchair; the arm rests being set too low; the foot rests being positioned too low; the seat depth being too long for an individual; the back support being too high or too low for an individual's needs; the seat height being too high for a foot propeller; or the rolling resistance being too great for a person who foot propels.

Let's review each of the above possible equipment factors. Let's assume a person has a wheelchair and seating system that is properly configured for that individual and the person is transferred into the wheelchair via mechanical lift. If that person is improperly positioned in the wheelchair at the outset, the person will lose the benefits of the positioning that were meant to be achieved. The pelvis may be positioned on a part of the cushion that provides little contour and allows for sliding over the flatter surface. In addition, a person who is improperly positioned in a wheelchair likely will be uncomfortable and may slide to get into a more comfortable position.

Sometimes simple adjustments to a wheelchair can influence the potential for sliding. For example, if the arm rests are too low for a person who wants the additional support provided through the arm rests, the individual may slide forward to bring the upper extremities to a height that can be supported by the low arm rests. Likewise, if the foot rests are positioned too low for an individual, the person will slide forward to achieve proper loading of the feet. (I have written previously about the importance of properly positioning the feet. Refer to the second last paragraph in my article on Practical Seating Considerations – Anterior Pelvic tilt) If either the arm rests or the foot rests are too low for a client, simple adjustments will help to position the client in a more optimal position.

Sometimes, the cause of the sliding is that the wheelchair seating is not fitted correctly for an individual. For example, if the wheelchair cushion is too long for someone, the person will slide forward to relieve the pressure and discomfort at the back of the knees. If the back rest is too tall or too vertical for an individual, the person will slide the pelvis forward to prevent the upper body falling forward. If the back rest is too short for an individual's needs, the person will slide the pelvis forward to allow the person to gain more support through the low back rest (i.e. to obtain support on the spine where it is desired).

For a person who propels the wheelchair either with a hand and a foot or with both feet, correct seat to floor height is important. If the seat to floor height is too tall for an individual, the person will scoot forward in an effort to obtain the proper heel strike and pull through to move the wheelchair.

Similarly, if the wheelchair has not been configured properly for the individual that foot propels, the individual may slide forward due to the effort required to propel the wheelchair. For example, if the front casters are loaded (i.e. the person's centre of gravity is forward of the rear wheels such that the person's mass is towards or over the front casters), the wheelchair is much more difficult to manoeuvre. If the rolling resistance of the tires or casters is too great for an individual, more effort will be required to foot propel, again causing a person to slide forward due to the effort required to propel the wheelchair through the lower extremities. (Look for a future Clinical Corner article on the importance of centre of gravity and wheelchair configuration for efficient propulsion.)

While there can be technical reasons that promote the potential for sliding, there can be also musculo-skeletal reasons that influence the potential for sliding. These musculo-skeletal factors include: presenting with posterior pelvic tilt and/or kyphosis; limited hip range of motion; limited knee range of motion; and tight hamstrings.

Let's review each of the above musculo-skeletal factors and how each may influence the potential for sliding in a wheelchair. If a person presents with a posterior pelvic tilt with the associated kyphosis, and if the seating and wheelchair configuration does not accommodate or correct this, depending upon whether the posture is fixed or flexible, respectively, gravity will continue to act on the person and sliding will occur. If a person has limited hip range of motion, such that the person cannot tolerate a typical 90 degree wheelchair setup, that person will slide into a posterior pelvic tilt to create a greater than 90 degree hip angle to provide improved comfort. Similarly, if a person has limited knee range of motion that is not accommodated in the front hanger angle, that person will slide into posterior pelvic tilt to reduce the knee angle, while keeping the feet supported on the foot rests. Lastly, if a person has tight hamstrings and the front hanger angle does not accommodate for this, the pelvis is pulled into posterior pelvic tilt and sliding can occur.

Let's take a closer look at tight hamstrings as a cause of sliding. The hamstrings attach to the pelvis and to the back of the knee. If the knee is extended beyond what is comfortable with respect to tight hamstrings, say with 60 or 70 degree hangers, the pelvis is pulled into posterior pelvic tilt to lessen the stretch on the hamstrings. With posterior pelvic tilt, there is the potential for sliding.

Some people present with multiple factors that contribute to sliding. For example, a person may have limited hip range of motion in addition to tight hamstrings. Multiple factors will require multiple solutions to address the potential causes of sliding.

This month, we have looked at some of the common equipment factors that contribute to sliding and how some simple adjustments can improve a person's positioning and minimize the potential for sliding. We have touched on the impact of centre of gravity and distribution of load and how that can impact the potential for sliding for someone who foot propels. We have also looked at some of the musculo-skeletal factors that can contribute to sliding. Next month, we will look at generic seating and wheelchair configuration solutions to address the underlying musculo-skeletal causes of sliding.

References

1. Batavia, M. (2010). The Wheelchair Evaluation. A Clinician's Guide. (2nd ed.). Sudbury, MA: Jones and Bartlett Publishers
2. Cooper, R. (1998). Wheelchair Selection and Configuration. New York: Demos Medical Publishing
3. Dennison, I. (N.D.) Wheelchair Selection Manual. Retrieved from http://www.assistive-technology.ca/studies/wheel.pdf
4. Jones, D. (1995). Real Solutions. Retrieved from http://www.wheelchairnet.org/
5. Rader, J., Jones, D., and Miller, L. (N.D.) Individualized Wheelchair Seating for Older Adults. Retrieved from http://www.primaris.org/