Wheelchair Positioning And Propulsion
The type of wheelchair, position of the person in the chair and propulsion technique also has a significant impact on shoulder demand.
Type of wheelchair
Determining whether power, power assist or manual wheelchair will be most functional and appropriate for a patient is the first step in prescribing effective and efficient mobility. Considering cushion weight, stability and pressure relieving needs are critical as well.
The following are general guidelines and considerations when prescribing wheeled mobility for different clinical Spinal Cord Injury patients.
- C1-C4 complete injuries
- Complete Cervical SCI with poor scapular stability. (Manual propulsion may place patient’s rotator cuff in a high impingement risk position and long thoracic nerve at risk for stretch injury).
- Middle Age to Geriatric Patient
- History of Shoulder Injuries or progressing pain.
- Inability to negotiate uneven surfaces, ramps or hills with power assist or manual, regardless of level of injury.
Power wheelchairs, with the exception of power add on units and a few power chairs that can break down, cannot be placed in a car or car trunk. The power add on units and power chairs that can break down are extremely heavy and difficult to lift into a car. The wheelchair user will need to utilize public or van transportation.
Power Assist Wheelchair
Wheels have instrumented handrims and motors within the wheel hub which assist the patient in manual propulsion.
- Patients with strong C5, C6, C7, C8 and below, who are able to propel a manual chair, but have difficulty with carpet, ramps, hills, uneven surfaces; or fatigue over time in manual chairs.
- Age and shoulder pain/injuries also are considerations. Protecting the shoulders in an aging or high shoulder injury risk patient, while still providing manual wheelchair benefits of low level exercise and transportability can be accomplished with a power assist chair.
- Wheels weigh up to 25 pounds and can be difficult to lift into car for patient or potentially for family member. Will this impact patient’s ability to travel in car? Do they use van/public transportation?
- Can be appropriate as high as C6 and at most levels below that, with considerations of age, shoulder condition and pain.
Setup is critical:
Studies suggest adjustable rigid chairs (versus folding) are chair of choice if functional for patient.6
Clinical Reasons for rigid chair:
- More efficient with lower rolling resistance secondary to less moving parts than folding chairs, light weight and camber. Camber allows less of the wheel to contact the surface, which decreases rolling resistance. Less moving parts allow more of the push to go towards moving the chair forward versus energy taken up in the folding frame.6
- Axle position adjustable, which allows for appropriate height of wheel axle, appropriate forward / back position and wheel camber to promote most effective biomechanical seat posture.
General guidelines for wheel position:
Axle Height Adjustment: Patient seated in chair with arm hanging at side. Fingertips should reach center of wheel axle.6 Caution: This forward / posterior adjustment in the prior picture must be made carefully, considering a patients sitting balance and safety. The farther forward the wheel is moved, the more “tippy” the wheelchair becomes. Progressing the wheel forward over time while allowing the patient to accommodate their sitting balance to that seat position will be more likely to produce an effective and safe wheelchair setup. Utilizing anti-tipper bars will also facilitate safety during the adjustment period after a wheelchair modification.
Studies have found that an axle position under or forward of the shoulder helps to maximize forward push force and reduces the forces transmitted superiorly or “up into” the subacromial space at the shoulder (5). The subacromial area is where classic rotator cuff impingement occurs.
Aligning the patient’s weight over the larger wheel also accomplishes the following:
- Decreased push frequency (the number of pushes necessary to maintain a desired speed)
- Decreased rolling resistance
- Decreased caster flutter
- Less of a tendency for the wheelchair to turn downward on a slanted road or sidewalk.
- Decreased rate of rise of push force (This will be discussed in the next section.)6
Having the person demonstrate a wheelie can be a general guide to how a wheelchair is setup. If the person can balance with the casters only a few inches off the ground, the chair is balanced well. If the balance point is with the casters several inches to a few feet off the ground, the chair is setup to be very stable, but not necessarily balanced for function.