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Proper fit of a wheelchair
How do you know when a wheelchair fits you? What happens if it doesn’t fit? Does one size fit all? Not usually. Especially for full-time users.
Wheelchairs come in all shapes and sizes. People who have issues with immobility or decreased sensation frequently cannot maintain proper positioning or are unaware that they have swayed from an upright, symmetrical posture. Asymmetrical posture can lead to problems with function, skin integrity, breathing, swallowing and digestion. For these people, it is imperative that the seating system be measured appropriately for them.
Important anatomical measurements to consider are hip width, femur or upper leg length, lower leg length, trunk height, buttock to elbow (when bent) height, chest width, chest depth, and forearm length, among others. These measurements can then be translated into equipment dimensions by a therapist or equipment supplier when the wheelchair and seating components are ordered.
What happens if a seating system doesn’t fit right?
Typically, the seat width is usually close to the hip width-or widest part of the body (taking into consideration recent weight gain/loss, seating components, and large postural deformities). If the seat width is too wide, it can: 1) Create a pelvic obliquity (one side of the pelvic higher than the other) and scoliosis (lateral curve of the spine) 2) Impair appropriate positioning of secondary supports of the seating system (trunk supports, thigh supports…) 3) Impair access to wheels/joystick/armrests 4) Impair accessibility (especially in manual wheelchairs as the overall chair width increases with increasing seat width).
If the seat width is too narrow, it can: 1) Create rotational deformities 2) Cause discomfort 3) Increase pressure on the lateral thighs (trochanters) or lower legs.
The seat depth should be slightly shorted than the upper leg/femur length (taking into consideration functional issues such as foot propulsion/leg management; pressure distribution; knee range of motion, leg length discrepancies/leg alignment; hanger angle of the legrest). If the seat depth is too long, it can: 1) Create posterior pelvic tilt, kyphosis, sliding out of seat, shear (overall contributes to poor posture, risk of skin breakdown and need for frequent repositioning) 2) Increases overall frame length (impairs maneuverability/increases turning radius) 3) Impede transfers (can’t get all the way back on the seat).
If the seat depth is too short, it can: 1) Cause hip external rotation and abduction 2) Increase pressure on IT’s 3) Impede transfers (less space to clear the tire for lateral transfers when using a manual wheelchair).
Seat height depends on many factors. Generally, a seat height that provides 2” of ground clearance under the footrests is the minimum seat to floor height. Access to the handrims for propulsion, transfer heights, and functional reach are some other factors to consider when determining seat height. Someone who propels with one or both feet requires a lower seat to floor height than anyone else to achieve adequate contact with the ground. If the seat height is too high, it can: 1) Cause foot propellers to slide out of chair 2) Impair access to wheels (leading to inefficient propulsion) 3) Impair accessibility (van, tables-raises head/knee height).
If the seat height is too low, it can: 1) Impair transfers (sit-stand, sliding board/depression to higher surfaces) 2) Decreased ground clearance 3) Impair accessibility (lower overall height impairs ability to reach objects with arms).
Legrest length/footplate height
The length of the legrest should be set so that the thigh rests parallel to the cushion surface with the foot comfortably placed on the footrest. Ankle plantar flexion contractures and other foot deformities need to be taken into consideration when the legrest length is determined to prevent the thigh from rising off the cushion surface. If the legrest length is set too long, it can: 1) Cause increased pressure on posterior thigh, leg edema, and hip internal rotation on upholstery seating 2) Decrease ground clearance 3) Cause sliding down in seat to meet footplates.
If the legrest length is set too short, it can: 1) Increase pressure on ischial tuberosities (sitting bones), cause hip abduction pressure against legrest hangers.
The back height is measured from person’s buttocks to top of shoulder. The placement of a wheelchair back is dependent on function and postural deformities: UE propulsion, balance, kyphosis. If the back height is too high, it can: 1) Impair propulsion, scapular mobility 2) Lead to kyphotic posture 3) Impair sitting balance.
If the back height is too low, it can: 1) Lead to kyphotic posture 2) Impair sitting balance 3) Cause inappropriate placement of anterior support devices for the shoulder/chest.
Back width is typically determined by the seat width, but can be different from the seat width with certain wheelchair back choices. Chest width and the need for external trunk supports are important considerations. If the back width is too wide, it: 1) May inhibit the ability to place secondary supports (trunk supports) in appropriate place 2) May impede arm function.
If the back width is too narrow, it can cause: 1) Edges/backposts dig into back 2) Insufficient room for trunk supports 3) Rotational deformities.
Armrest height needs to meet height of the flexed elbow when seated. Consider addition of lap trays, custom arm supports. If the armrest is set too high, it can: 1) Increase pressure on glenohumeral joint and cause pain 2) Cause difficulty maneuvering joystick.
If the armrest is set too low, it can: 1) Create kyphosis or scoliosis 2) Increase pressure on ischial tuberosities 3) Cause or worsen shoulder subluxation.
Arm length is measured from elbow to wrist or end of fingertips. Armrest length varies depending on amount of support required. If armrest length is too long, it can: 1)Limit desk/table clearance.
If the armrest length is too short, it: 2) May impair sit-stand transfers 3) May not support lap tray/items on it.
Does it matter if a seating system fits right? Absolutely!
|Author:||Chris Maurer, MPT, ATP|
|Affiliation:|| Shepherd Center, Atlanta, GA
Center for Assistive Technology and Environmental Access, Georgia Institute of Technology