Wheelchair Prescription Basics
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Direct answer
Measure the hips, add five centimetres for seat width; measure buttock to popliteal fossa, subtract five centimetres for seat depth — those two rules prevent the twin failures of wheelchairs: too wide, and the user cannot self-propel efficiently; too deep, and popliteal vessels are compressed and posture collapses into posterior pelvic tilt. Seat height must clear the footrests about five centimetres above the ground while allowing a functional reach if the user self-propels, backrest height follows trunk control (lower for active users, higher or laterally contoured for weak trunks), and armrests sit at approximately 90 degrees of elbow flexion. Prescription then layers on pressure management — the cushion is part of the chair, not an accessory — matched to the user's neurological status, environment and transfer method, not to whatever stock sits in the store.
What you must remember
- The measurement set: seat width = widest hip point + 5 cm (2 inches); seat depth = posterior buttock to popliteal fossa − 5 cm; seat height = ground to popliteal fossa with the footplate clearing about 5 cm; backrest height = seat to axillary fold (low) or scapula/shoulder (higher support); armrest height set to 90° elbow flexion with shoulders relaxed.
- Why each tolerance exists: extra width wastes propulsion energy; excess depth compresses hamstrings and causes sacral sitting; insufficient depth concentrates pressure on the ischial tuberosities.
- Pressure management: ischial and sacral sores are the disaster to design against — select cushion by risk (foam cheapest, gel distributes, air-filled like ROHO highest relief but needing maintenance), and train push-ups or weight shifts every 15-30 minutes for 30-90 seconds in users with sensation loss.
- Tilt-in-space versus recline: tilt preserves hip and knee angles while shifting weight off the ischia (preferred for pressure and tone); recline opens the hip angle (useful for toileting and transfers but risks shear and extensor tone).
- Chair types by user: lightweight active chairs for independent users, depot chairs for institutional use, powered chairs for poor arm function, and a forward axle position to lighten the castors for active users.
- Postural inserts: lateral trunk supports, adductor wedges, abductor pommel, headrests, anti-thrust seats — prescribed for the neurological user whose pelvis slides into obliquity or rotation.
- Indian access route: the ADIP scheme funds or subsidises wheelchairs and aids through implementing agencies including ALIMCO, with cost sharing linked to income — the practical prescription pathway in government settings.
Prescribing for one spinal cord injury patient
A 24-year-old with T6 complete paraplegia, six weeks post-injury, needs his first chair. Measurements taken seated on a firm surface: hip width 40 cm, buttock-popliteal 46 cm — so a 45 cm wide seat would be wrong (too wide) and 40 cm right, with 41 cm depth. He is a candidate for a lightweight folding frame with a low backrest since trunk control is intact; a gel-foam cushion is selected because he lacks sensation below the lesion but sits actively all day. Training is the actual therapy: sliding-board then depression transfers, timed weight shifts, and propulsion retrained to long semicircular pushes — shoulder overuse is the epidemic of the second decade post-injury. His home visit reveals a 3-cm door sill and a narrow bathroom, so ramps and a commode chair join the prescription, with daily skin inspection taught. Contrast a C5 tetraplegic: powered chair, tilt-in-space to 45 degrees, contoured seating, joystick — same ward, entirely different chair, because prescription follows level, function and environment, in that order.
Exam angles and the Indian reality
Theory questions ask to enumerate prescription measurements, cushion selection criteria, or tilt-in-space versus recline — marks-in-the-numbers answers where "plus 5, minus 5" centimetres and the 15-to-30-minute pressure relief schedule carry the grade. The viva favourite is which chair for which patient — an active paraplegic versus a frail elderly user versus a child with cerebral palsy — expecting frame, backrest, cushion and add-on reasoning. Indian practice keeps the ADIP scheme central: cost-shared wheelchairs routed through ALIMCO and authorised agencies make the therapist's prescription double as subsidy documentation, and depot-model mismatch is common — knowing which compromises are tolerable (weight) and which are not (cushion, width) is real clinical skill. One sober sentence earns respect: the commonest cause of a pressure ulcer is a chair delivered without training.
Frequently asked questions
How is seat width measured for a wheelchair?
Across the widest point of the hips in sitting, with five centimetres added to allow hand clearance during propulsion.
Why is five centimetres subtracted from the buttock-to-popliteal measurement for seat depth?
To prevent the front edge digging into the popliteal fossa, which compresses neurovascular structures and pushes the pelvis into a posterior tilt.
How often should pressure relief be performed, and for how long?
Every 15-30 minutes for 30-90 seconds — by push-up, lateral lean or forward lean — or by tilt-in-space where active relief is impossible.
When is tilt-in-space preferred over recline?
For pressure relief and postural management in users with poor trunk control or abnormal tone, because tilt shifts weight off the ischia without opening the hip angle and causing shear.
What does the ADIP scheme provide?
Government of India financial assistance for purchase and fitting of aids and appliances, including wheelchairs, delivered through implementing agencies such as ALIMCO with income-linked cost sharing.