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PRESSURE & POSTURE IN WHEELCHAIR SEATING
DEFINITION OF PRESSURE
Pressure = Force / Area
ANATOMY OF THE SKIN
Epidermis
Dermis
Subcutaneous Layer
EFFECTS OF PRESSURE
• Occludes capillaries
• Restricts flow of oxygen and vital nutrients
• Lymphatic drainage restricted
• Cell deformation under sustained pressure can also lead to cell death
DEFINITION OF PRESSURE ULCERS
“A pressure ulcer is localised injury to the skin and/or underlying tissue usuallyover a bony prominence, as a result of pressure, or pressure in combination with shear”
International NPUAP-EPUAP Pressure Ulcer Definition
SHEAR
• Forces parallel to the seating surface
• Often created by the effects of gravity
SEVERITY OF PRESSURE ULCERS
GRADE I: Nonblanchable Erythema
“Intact skin with non-blanchableredness of localised area, usually over a bony prominence.”
NPUAP-EPUAP
SEVERITY OF PRESSURE ULCERS
GRADE II: Partial Thickness Skin Loss
“Partial thickness loss of dermis presenting as a shallow open ulcer with a red pink wound bed, without slough…”
NPUAP-EPUAP
SEVERITY OF PRESSURE ULCERS
GRADE III: Full Thickness Skin Loss
“Full thickness tissue loss. Subcutaneous fat may be visible but bone, tendon or muscle are notexposed.”
NPUAP-EPUAP
SEVERITY OF PRESSURE ULCERS
GRADE IV: Full Thickness Tissue Loss
“Full thickness tissue loss with exposed bone, tendon or muscle.”
NPUAP-EPUAP
PRESSURE ULCER DEVELOPMENT
PRESSURE
MOBILITY
ACTIVITY
SENSORY PERCEPTION
TISSUETOLERANCE
PRESSURE ULCER
DEVELOPMENT
EXTRINSIC FACTORS
INTRINSIC FACTORS
EXTRINSIC FACTORS
• Localised Pressure
• Shear & Friction
• Poor Posture
• Time
• Temperature
• Moisture
INTRINSIC FACTORS
• Impaired Reaction to Pressure
• Restricted Movement
• Impaired Sensation
• Decreased Tissue Tolerance
• Heart Problems
• Vascular Disease
• Diabetes
• Serious Illness
• Old Age
• Incontinence
• Neurological Conditions
• Medication
PREVENTATIVE MEASURES
• Maintain regular changes in position and avoid positioning over areas of erythema whenever possible.
• Keep the skin clean and dry. Manage any incontinence issues.
• Maintain good nutrition.
• Use appropriate equipment where applicable.
P R I N C I P L E S O F
CUSHION DESIGN
PRESSURE DISTRIBUTION IN NEUTRAL SITTING
Feet (19%)
Arms (2%)
Back (4%)
Thighs & Buttocks (75%)
PRESCRIBING FOR PRESSURE
Goals
USER CHARACTERISTICS
TASKCHARACTERISTICS
CUSHIONCHARACTERISTICS
DESIGNING FOR PRESSURE
CUSHIONCHARACTERISTICS
• Redistribution of Pressure
• Management of Shear Forces
• Postural Support
• Management of Vibration and Shock
• Thermal Properties
DESIGNING FOR PRESSURE - MATERIALS
• Flexible, open-cell foam
• Quick recovery after compression
• Permeable
POLYURETHANE FOAM (PU)
DESIGNING FOR PRESSURE - MATERIALS
• Rigid, light-weight, non-permeable, closed cell foam
• Shock absorbing properties
• Used in cushion bases to provide postural support in combination with a top conforming surface
POLYETHYLENEFOAM
• Slow recovery after compression
• Can dampen vibration and shock
• Contours to shapes more closely than standard PU foams
• Hardness sensitive to temperature and humidity
DESIGNING FOR PRESSURE - MATERIALS
VISCO-ELASTIC FOAM
DESIGNING FOR PRESSURE - MATERIALS
• ‘Liquid gels’ displace and conform to equalise pressure
• Baffles and compartments restrict flow
• The lower the viscosity the greater the shock absorbency
FLUIDS/GELS
DESIGNING FOR PRESSURE - MATERIALS
• Air moves between cells equalising internal pressure
• Compartments restrict movement to improve stability
• Set up and maintenance required
AIR
DESIGNING FOR PRESSURE - SHAPE
• Allows greater immersion and distributes pressure over a greater surface area
• Can improve dynamic stability
CONTOURING
DESIGNING FOR PRESSURE - SHAPE
• Reduces surface tension and increases pressure redistribution
• Greater ability to move with the user –reduces shear forces
SEGMENTATION
DESIGNING FOR PRESSURE - SHAPE
• Accommodates the Ischial Tuberosities
• Improves weight loading under the thighs
• Helps stabilise the pelvis
• Can prevent sliding forwards
ANTI-THRUST
DESIGNING FOR PRESSURE - SHAPE
• Allows standard products to be customised for individual clients
• Can cater for a range of pressure requirements and scenarios
MODULARITY
• Density
• Firmness
• Ability to return to original shape
Slab Molded
FOAM
Pressure Management is
dependent on distribution of
weight and pressure off of the
ischials and onto the lateral
trochanter shelf & femurs
SHAPE
.
ImmersionMaximizes surface contact area to reduce peak pressures.Pressure = Force/Area
Off-LoadingTransfers forcesaway from the ischialtuberosities with greaterweight bearing on thetrochanters, hips andthighs.
EnvelopmentFluid sac completelysurrounds the bonyprominences, evenduring position changes.
CUSHION DESIGN
Static • Support surface contour that prevents sliding and downward migration of the pelvis.
Dynamic • Flow of materials reduces tension between bony prominences and tissues during functional activities, wheelchair propulsion, accommodates movement within a specific range.
Optimal shear reduction addresses both static and dynamic shear without compromising posture.
SHEAR MANAGEMENT
ASSESSMENT TOOLS
MAT = Mechanical assessment tool
3 stages:
1. Assessment in existing seating system
2. Assessment in supine
3. Assessment in sitting
MAT EVALUATION
PRESSURE MAPPING AS AN ASSESSMENT TOOL
• Aim: to minimise peak pressures and maximise surface area
• Pressure gradients indicate the potential presence of shear forces
Pressure = Force / Area
PRESSURE MAPPING
How will your cushion map?
P R I N C I P L E S F O R
SEATING & POSITIONING
SEATING & POSITIONING
Assist individuals in achieving their goals and aspirations, while respecting lifestyle,
function, posture and skin protection by providing simple, effective, and safe seating
solutions
SEATING & POSITIONING
• Facilitate postural stability while allowing purposeful movement .
• Accommodate 3-dimensional anatomical shapes, working to match contours for optimal support and pressure redistribution.
• Wherever possible, support postures from within the contours of the seating system. If needed, complement with additional external components.
SEATING OBJECTIVES
SEATING & POSITIONING
• A comprehensive evaluation, including a physical assessment in both supine and sitting, is the foundation of all effective seating solutions. Where possible, trial seating in static and dynamic situations.
• The position of the pelvis directly impacts the spine, which in turn influences the position of the head and extremities.
GUIDING PRINCIPLES
SEATING & POSITIONING
• Determining if a posture is fixed or flexible is important for selecting appropriate seating solutions.
• The effect that seated posture has on breathing and swallowing should be a primary concern.
GUIDING PRINCIPLES
M A N A G E M E N T O F
COMMON SEATING AND POSTURAL PROBLEMS
Pelvic Stability
Contouring of the pelvic well provides lateral trochanteric support and anterior/posterior pelvic stability, promoting spinal extension for improved upper extremity function, head control and physiological function.
Note: Back support must be addressed for complete postural and skin protection solution.
STABILITY
POSTERIOR PELVIC TILT WITH KYPHOSIS
Cervical spine may hyper-extend to maintain a functional visual field
Scapula may protrude posteriorly
Flattened lumbar spine and increased thoracic kyphosis
Pelvis tilted posteriorly with the Anterior Superior Iliac Spine (ASIS) higher than the Posterior Superior Iliac Spine (PSIS)
Tendency for pelvis to slide forwards
CLINICAL PRESENTATION
POSTERIOR PELVIC TILT WITH KYPHOSIS
Consider anterior chest support
Consider support for upper limbs Firm back support that stabilises from the PSIS up to slightly above the apex of the kyphotic curve
Pelvic positioning belt beneath the ASIS
Contoured cushion to help stabilise the pelvis in a neutral position
FLEXIBLEPOSTURE
POSTERIOR PELVIC TILT WITH KYPHOSIS
Consider utilising tilt to achieve a more upright position and improve functional visual field and head position
If spinal process or ribs are prominent increase backrest depth for greater immersion
For a unilateral limitation in hip flexion, modify the cushion to split the sagittal seat angle to accommodate and try to achieve a level pelvis
Contoured cushion to support the pelvis
FIXEDPOSTURE
Provide a contoured back support to match shape of spine
ANTERIOR PELVIC TILT WITH HYPERLORDOSIS
May present with shoulder retraction
Pelvic to thigh angle less than 90 degrees
May present as exaggerated lumbar lordosis and result in decreased contact with the back support surface
Pelvis tilted anteriorly with ASIS lower than the PSIS
Trunk often extended to compensate for instability from anterior pelvic tilt
CLINICAL PRESENTATION
ANTERIOR PELVIC TILT WITH HYPERLORDOSIS
Consider anterior chest support
Each client will differ in preference of sagittal seat and back support angles, especially those with Muscular Dystrophy and Spina Bifida
Assess small incremental changes to seat slope and angle of back support the move the pelvis and spine into a neutral orientation
Provide back support at level of PSIS to reduce lordosisEarly use of powered seating to allow
independent adjustment for comfort and/or function balance
FLEXIBLEPOSTURE
ANTERIOR PELVIC TILT WITH HYPERLORDOSIS
Angle and depth adjustable back support
FIXEDPOSTURE
Angle rear of the seat lower than the front to balance trunk over the pelvis
PELVIC OBLIQUITY AND SCOLIOSIS
Shoulder often elevated on the oblique side
Increased pressure risk on oblique side
One side of the pelvis is lower than the other
The obliquity is referred to by the lower side of the pelvis
The spine is influenced by the oblique pelvis, resulting in scoliosis.
The spinal curve will be convex on the oblique (lower) side of the pelvis
CLINICAL PRESENTATION
PELVIC OBLIQUITY AND SCOLIOSIS
Lateral supports
Lateral/hip supports
FLEXIBLEPOSTURE
Ensure lateral depth is deep enough to support the trunk
Lateral trunk supports can be used to provide either 3 or 4 key points of control to support or minimise progression of scoliosis
Alternate approach – deep contoured back with lateral contour positioned to support the ribcage
If flexible, build up the cushion under the lowest ischial tuberosity to encourage a level pelvis
PELVIC OBLIQUITY AND SCOLIOSIS
FIXEDPOSTURE
Ensure lateral depth is deep enough to support the trunk
Contoured back with integral lateral support
If fixed, build up support under the highest ischial tuberosity to increase weight bearing on high side
HIP ABDUCTION
Movement of the femur away from midline
Can be unilateral or bilateral
Lower extremities are separated further apart from neutral
CLINICAL PRESENTATION
HIP ABDUCTION
Try to align femurs in neutral using contoured cushion or distal lateral supports
FLEXIBLEPOSTURE
Contoured cushion to align lower extremities
Accommodate with custom contoured seating
FIXEDPOSTURE
HIP ADDUCTION
Movement of femurs toward midline
Can be unilateral or bilateral
CLINICAL PRESENTATION
HIP ABDUCTION
Use seat rigidiser or solid seat pan
Trial distal medial thigh support or contoured seating
FLEXIBLEPOSTURE
Contoured cushion to align lower extremities
Accommodate with custom contoured seating
FIXEDPOSTURE
Cushion rigidiser contoured to eliminate ‘hammock effect’ of sling upholstery
PELVIC ROTATION
One hip is abducted, the other adducted
One knee may appear further forward
One ASIS and therefore hip is further forward in the seat than the other
CLINICAL PRESENTATION
PELVIC ROTATION
Use a contoured cushion to align the pelvis in neutral and support lower extremity posture
FLEXIBLEPOSTURE
Use a pelvic positioning belt to bring hips back into alignment
In order to maintain head and shoulder in a neutral position for function, you may need to maintain some asymmetry in the pelvis
PELVIC ROTATION
FIXEDPOSTURE
Accommodate limited hip flexion by opening seat to back angle
If present, measure the leg length difference
Order cushion for longer leg length and specify amount to cut back on shorter side
Contoured back support rotated to accommodate any mild/moderate trunk rotation, support the spine and distribute pressure