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Wheelchair Prescription
A special note regarding the difference between Bariatric and standard wheelchairs. The center of body
mass is located somewhere about 1 inch forward of the second sacral vertebrae in the average person.
Wheelchair manufactures know that having ~ 80% of body weight over the rear axle maximizes ease of
wheelchair propulsion by unweighting the front caster wheels. In the Baratric client this center of body
mass may be several inches forward when compared to the client of average weight. For this reason, the
specialized bariatric wheelchair has a rear axle displaced further forward relative to the standard
wheelchair just to achieve the same ~ 80% body weight over the rear axle. Orthopedically this forward
axle also allows mechanical advantage for the bariatric client to propel by means of a full arm push and
not wrist extension seen in wheelchair prescription where the axle is too far behind the patient's
shoulder.
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Wheelchair Prescription:
Actual body weight. If clients body type is "pear like" consider potential of stable weight and stable w/c
width indication over time. If client body type is "apple like" consider potential for fluctuating weight. If
deciding between two sizes consider opting for the larger size and potentially wider w/c. The final
wheelchair design selected should, of course, meet the dynamic load potential of the intended client.
Measuring:
When measuring this client population, if possible have the client sit on a hard surface such as a therapy
mat, original wheelchair, or on a square of firm plywood. The client's thighs should be level and not
upward or downward sloping relative to the hip joint. The lower leg should be in a comfortable vertically
oriented posture. This posture allows for easy access to measure the client from a true postural set,
otherwise not possible from a soft surface. Once the overall height is determined, the next consideration
in W/C prescription is measurement of the pelvic region. This is the client's primary weight bearing
surface. W/C measurement is possible while the client is lying in bed, however, very subject to error as
adipose tissue sags posteriorly rather then inferiorly as observed in sitting postures. The supine
measurement therefore contributes to undersized width and excessive depth as the clients legs do not
abduct as in the sitting posture where abdominal contents drift inferiorly between the clients legs.
1. Seat Height:
With feet flat on the floor and the shin in vertical posture, measure from the back of the heel to underside
of knee. The client should wear typical footwear and again the thighs should be level relative to the hip
joint prior to measurement. This will allow for proper foot rest length and overall W/C height which is
so vital in W/C propulsion for those who tend to achieve propulsion by combination of hand and foot
use. W/C floor to seat height is also critical for sit to stand activities. For individuals who are primarily
exercise ambulators, a lower seat height may be indicated allowing community propulsion while for
individuals who ambulate (functional ambulators) to vital rooms or bathrooms, a higher seat height may
be indicated. Recall that W/C cushions will add to the height of the finished sitting surface. Extra low or
bariatric hemi-wheelchairs are also available providing sufficient mechanical advantage for those who
rely upon one sided (unilateral) W/C propulsion or bipedal W/C propulsion.
2. Seat Depth:
Measure from the back of the buttocks to within ~ 1 to 2 inches of the back of knee. The completed W/C
should allow for approximately 1 to 2 inches of space between the back of the clients knee and the front
of the W/C seat, thereby preserving circulation to the lower leg while maximizing the clients weight
bearing surface and leg mobility during foot assisted propulsion. The seat surface should support the
entire gluteal region. If a client has a posteriorly bulbous gluteal region, then a contoured cushion or strap
backrest may help provide sufficient trunk support.
3. Seat Width:
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Measure widest part of client in the seated posture. Again consider apple versus pear. A pear shaped
individual having greater gluteal femoral weight distribution may be widest near the front edge of the
seat. Excessive W/C width will restrict mobility about environmental barriers, increase difficulty of both
turning and forward propulsion while decreasing armrest support with resulting potential for back pain.
The completed W/C will allow for approximately 1 to 2 inches of width on either side of the client for
winter clothing, client weight shifting during pressure relief, and if necessary room for possible lift
devices such as slings. On occasion clients may opt to remove W/C push rims to accommodate narrow
doorways or environmental barriers.
4. Backrest Height:
Measure from the seat surface to mid shoulder blade height. The back rest generally should reach to mid
shoulder blade level in height and support the apex of the client's back to diminish potential for postural
back pain thus providing for adequate pressure relief while allowing maximal shoulder blade mobility. If
the client is in a reclining chair then additional upper thoracic support may be indicated. More agile
clients may prefer a backrest that is positioned vertically just ~ 1 inch below the shoulder blade allowing
for maximal upper body mobility over their lower trunk. in sitting postures. If a the client should have
localized excessive tissue bulk causing partial contact to their backrest. A strap or laced back backrest
may be indicated to provide sufficient support for that unique body type.
5. Armrest Height:
Measure directly from the sitting surface to the bent elbow having the forearm parallel to the seat. Recall
that a seat cushion may add the height of the seat and equally add to the height of the armrest.
Appropriate armrest height is determined from this measurement and is important for decreasing neck
and thoracic back pain by providing adequate support for the shoulder girdle. Remember that respiratory
impaired individuals derive increased respiratory support by leaning upon their forearms and thereby
increase depth of breathing by reverse action of upper body muscles. This is common in the obese client
with respiratory compromise or congestive heart failure. Pressure relief, weight shifting and sit to stand
activities may also be augmented by arm rest height in some individuals.
Hard Seat Applications:
Solid hard seat applications provide superior weight bearing distribution and overall superior orthopedic
alignment. To the client, this is experienced in decreased muscular pain related to prolonged poor
postures. The hard seat application tends to be more durable making them ideal for clients who rely upon
their W/C as a primary source of mobility. The difficulty in providing hard seat applications are financial
and client familiarity with side folding W/C's.
Specific medical indications which require hard seat applications include:
presence of neurologic disease with spasticity,
post stroke or other forms of paralysis and
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severe orthopedic deformity.
Tires:
Consider that hard solid tires have increased durability especially in turning. Pneumatic tires provide a
smoother ride and return greater energy to the user, but have a tendency to roll off the rim during turning
and may experience premature sidewall tire fatigue over time. Further, pneumatic tires and spoked rims
require continued maintenance not necessary in the mag wheel solid tire application. Pneumatic tires also
can sustain leaks resulting in flats, therefore tend to be used for the client who requires performance.
Adjustable Backrest Indications:
In the past, Velcro strapping within W/C back rest has been used to accommodate client orthopedic and
neurologic deformity, creating a custom fit pressure-relief surface. For the bariatric client, strapped or
laced backrest have evolved independently, allowing posterior translation of seat depth, thereby placing
the client's center of gravity over the rear axle for effective propulsion. Such adjustable backrest also
allow adjustment to accommodate excessive posteriorly displaced tissue bulk often seen in the client with
a bulbous gluteal region.
Reclining W/C Applications:
Clients unable to sit vertically because of excessive abdominal tissue bulk limiting hip flexion range of
motion, or excessive tissue contributing to respiratory resistance in upright sitting postures may require a
reclined backrest application. Other medical conditions restricting individuals from upright postures
include orthostatic hypo tension, psychological influences and fear often more apparent during initial
phases of rehabilitation.
Power W/C Applications:
Recommendations include: Order designed heavy duty wheelchairs rather then attempting to upgrade
standard power w/c applications.
Lesser applications are susceptible to metal fatigue upon impact and shear forces often at caster mounts,
caster wheel axles, foot plate mounts, and general frame integrity. Motor durability issues should also be
obvious. Many individuals require power applications due to cardiac insufficiency. Some third party
payers will reimburse for power W/C's if prescription will dramatically increase client participation in
community activities such as employment while decreasing the clients dependency upon medical services.
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