Wheelchair seating and positioning is a critical component of care for patients with neurological conditions who are non-ambulatory or have limited mobility. The primary goals include maintaining optimal posture, preventing pressure injuries, maximising function, and promoting comfort. The pelvis serves as the foundation of the seating system, and neutral pelvic positioning is essential for proximal stability and distal function. Proper seating reduces the risk of secondary complications including pressure ulcers, scoliosis progression, hip subluxation, and respiratory compromise. A multidisciplinary approach involving occupational therapists, physiotherapists, orthotists, and orthopaedic surgeons is essential for optimal outcomes.

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The Pelvic Foundation

The pelvis serves as the foundation of the seating system and the key to proximal stability. Proper pelvic positioning enables optimal trunk alignment, head control, and upper limb function. The pelvis should be positioned in neutral alignment, with the ASIS landmarks level and the pelvis neither excessively tilted anteriorly nor posteriorly. [1]

Neutral pelvic position characteristics:

• ASIS and pubic symphysis in vertical plane
• Weight distributed evenly on ischial tuberosities
• Lumbar lordosis preserved
• Thighs parallel to seat surface

Posterior pelvic tilt consequences:

• Sacral sitting with increased sacral pressure
• Loss of lumbar lordosis
• Thoracic kyphosis compensation
• Cervical hyperextension for visual field
• Increased risk of pressure injuries
• Compromised respiratory function

Biomechanical Principles

The seated posture involves a kinetic chain from the pelvis through the spine to the head. Optimal positioning requires understanding of force distribution, pressure management, and postural alignment. [2]

Key biomechanical considerations:

• Seat depth affects thigh support and popliteal pressure
• Seat width affects lateral trunk support availability
• Seat-to-back angle affects posture and pressure distribution
• Footrest height affects thigh loading and pelvic position
• Armrest height affects shoulder positioning and transfers

Goals of Seating Intervention

1. Posture and Alignment:

• Maintain neutral pelvic position
• Preserve or improve spinal alignment
• Support head position for function
• Prevent or accommodate deformity

2. Pressure Management:

• Distribute forces over maximal area
• Reduce peak pressures at bony prominences
• Enable regular pressure relief activities
• Prevent tissue breakdown

3. Function Optimisation:

• Facilitate upper limb reach and manipulation
• Enable safe swallowing and breathing
• Support communication and vision
• Allow mobility and environmental access

4. Comfort and Tolerance:

• Maximise sitting duration
• Reduce pain and fatigue
• Improve quality of life
• Promote participation in activities

Assessment of Pelvic Position

Clinical assessment of pelvic position requires palpation of bony landmarks with the patient seated. The ASIS landmarks are the primary reference points for determining pelvic tilt and obliquity. [3]

Assessment technique:

1. Patient seated on firm surface
2. Palpate bilateral ASIS landmarks
3. Determine relative position to assess tilt
4. Compare ASIS heights to assess obliquity
5. Assess rotation by comparing ASIS to PSIS planes
6. Determine if deformity is fixed or flexible

Pelvic Tilt

Neutral pelvic tilt:

• ASIS and pubic symphysis in same vertical plane
• Optimal for pressure distribution
• Preserves lumbar lordosis
• Goal for most seating interventions

Posterior pelvic tilt:

• ASIS posterior to pubic symphysis
• Common in hypotonic patients
• Causes sacral sitting
• Increases sacral and coccygeal pressure
• May be fixed or flexible

Anterior pelvic tilt:

• ASIS anterior to pubic symphysis
• Less common in wheelchair users
• May occur with hip flexion contracture
• Can cause increased lumbar lordosis

Pelvic Obliquity

Pelvic obliquity refers to asymmetric height of the ASIS landmarks in the coronal plane. One side of the pelvis is higher than the other. [4]

Causes of pelvic obliquity:

• Leg length discrepancy
• Hip contracture (adduction/abduction asymmetry)
• Scoliosis (pelvic obliquity secondary to spinal curve)
• Muscle imbalance (asymmetric tone)
• Fixed bony deformity

Management of obliquity:

• Determine if flexible or fixed
• Flexible obliquity can be corrected with seating
• Fixed obliquity must be accommodated
• Unilateral seat elevation or contouring
• Consider orthopaedic intervention for severe fixed cases

Pelvic Rotation

Pelvic rotation occurs when one ASIS is anterior relative to the contralateral side in the transverse plane. This is often associated with windswept hip deformity.

Windswept deformity:

• Combined hip abduction on one side and adduction on the other
• Creates apparent limb length discrepancy when supine
• Associated with pelvic rotation and obliquity
• Common in non-ambulatory cerebral palsy
• Difficult to accommodate in seating systems

Differential Diagnosis: The Deteriorating Seated Posture

A common exam and clinic scenario is the patient whose sitting has "got worse." The differential is structural, not a single diagnosis — the value lies in distinguishing causes that respond to seating adjustment from those needing surgical or medical intervention.

Pathophysiology of Pressure Injuries

Pressure injuries develop when sustained external pressure exceeds capillary closure pressure (approximately 32 mmHg), leading to tissue ischaemia and necrosis. Additional contributing factors include shear forces, friction, moisture, and nutritional status. [5]

Risk factors for pressure injuries:

• Impaired sensation (SCI, neuropathy)
• Impaired mobility
• Incontinence
• Malnutrition
• Cognitive impairment
• Previous pressure injury
• Bony prominences
• Muscle atrophy

High-risk seated pressure areas:

• Ischial tuberosities (highest risk when seated)
• Sacrum and coccyx (especially with posterior pelvic tilt)
• Greater trochanters (lateral positioning)
• Spinous processes (kyphotic patients)
• Scapulae (thin patients with high backrests)

Pressure Mapping Technology

Interface pressure mapping provides objective measurement of pressure distribution between the patient and seating surface. This technology uses sensor arrays to quantify pressure at multiple points and display results as colour-coded maps. [6]

Clinical applications of pressure mapping:

• Cushion selection and comparison
• Positioning adjustment optimisation
• Identification of high-pressure areas
• Documentation for funding justification
• Patient and caregiver education
• Outcome measurement

Pressure mapping parameters:

• Peak pressure (maximum value at single point)
• Average pressure across contact area
• Pressure gradient (rate of change)
• Contact area (distribution of load)
• Pressure time integral (duration factor)

Cushion Selection Principles

Cushion selection depends on pressure injury risk level, positioning needs, transfer ability, lifestyle factors, and budget constraints. [7]

Selection considerations:

• Risk level (low, moderate, high, very high)
• Postural stability requirements
• Transfer method and frequency
• Weight and build of patient
• Continence status
• Maintenance capacity
• Environmental factors (temperature, moisture)

Seating System Types

Linear (Planar) Systems:

• Flat surfaces at various angles
• Adjustable and versatile
• Suitable for flexible postures
• Lower cost
• Examples: solid seat insert, flat back support

Contoured (Custom-Moulded) Systems:

• Shaped to patient anatomy
• Maximum contact and support
• Optimal for fixed deformities
• Higher cost and complexity
• Examples: custom-moulded back, seating simulator cast

Trunk Support Components

Lateral trunk supports:

• Provide coronal plane stability
• Prevent or accommodate scoliosis
• Position varies with curve pattern
• May be fixed or swing-away
• Must not impede respiration

Back support systems:

• Solid insert replaces sling upholstery
• Provides consistent postural support
• May be flat, contoured, or custom-moulded
• Height affects head control and comfort
• Angle affects pelvic position

Pelvic Positioning Devices

Pelvic guides/laterals:

• Position pelvis in midline
• Prevent lateral migration
• May accommodate or correct obliquity

Anterior pelvic supports:

• Seat belt positioning (45-degree angle optimal)
• Subasis bar (padded bar below ASIS)
• Positioning belt systems
• Prevent forward sliding

Hip positioning aids:

• Pommel or medial thigh support
• Prevents adduction
• Abductor wedges for hip positioning
• Thigh guides for rotation control

Head Support Systems

Indications for headrest:

• Poor active head control
• Fatigue with prolonged sitting
• Transportation safety
• Posterior head positioning

Headrest types:

• Flat posterior support
• Contoured occipital support
• Circumferential support (complex needs)
• Dynamic headrests (allow movement)

Condition-Specific Seating Management

Hip Surveillance and Management

Non-ambulatory children with cerebral palsy are at high risk for hip displacement, with prevalence of 60-90% in GMFCS levels IV and V. Hip surveillance protocols recommend regular clinical and radiographic monitoring. [11]

Hip surveillance parameters:

• Clinical hip examination every 6 months
• Anteroposterior pelvis radiograph annually (minimum)
• Migration percentage calculation
• Acetabular index measurement
• Assessment of hip pain and function

Migration percentage thresholds:

• Less than 30%: observation, continue surveillance
• 30-50%: increased surveillance, consider soft tissue surgery
• More than 50%: high risk for dislocation, consider reconstruction
• Dislocated: salvage procedures may be needed

Seating implications of hip surgery:

• Soft tissue releases may improve positioning
• Bony procedures require healing before seating
• Post-operative seating assessment needed
• Accommodating versus corrective approaches

Spinal Surgery Considerations

Neuromuscular scoliosis is progressive in non-ambulatory patients and frequently requires surgical intervention. Spinal fusion significantly impacts seated posture and function. [12]

Indications for spinal fusion:

• Progressive curve despite bracing
• Curve magnitude affecting function
• Pelvic obliquity causing sitting imbalance
• Respiratory compromise from curve
• Pain related to deformity

Fusion extent considerations:

• Upper level depends on curve pattern
• Lower level typically to pelvis in neuromuscular
• L5/S1 or iliac fixation common
• Preserves versus sacrifices lumbar motion
• Sitting balance goals influence levels

Post-fusion seating changes:

• Loss of compensatory spinal motion
• Fixed spine requires seat angle matching
• Improved pelvic alignment often achieved
• May need new seating system
• Function may improve or decline

Limb Procedures and Seating

Orthopaedic procedures on the limbs affect positioning requirements and seating prescription.

Lower limb considerations:

• Hip flexion contracture release may improve sitting angle
• Knee flexion contracture affects footrest positioning
• Foot deformity correction improves footplate placement
• Limb length discrepancy affects pelvic position

Upper limb considerations:

• Elbow and wrist positioning for function
• Hand support needs at armrest level
• Splinting integration with seating

Core Team Members

Occupational Therapist:

• Seating and positioning assessment
• Functional upper limb evaluation
• Equipment prescription
• Home and school environment assessment
• Activities of daily living training

Physiotherapist:

• Physical assessment and mobility
• Postural management programmes
• Respiratory physiotherapy
• Strengthening and stretching
• Gait training when applicable

Orthotist:

• Fabrication of custom seating components
• Orthotic devices for positioning
• Technical expertise in materials
• Fitting and adjustments
• Maintenance and repairs

Rehabilitation Engineer:

• Complex seating solutions
• Power mobility systems
• Electronic access devices
• Environmental controls
• Technical problem-solving

Orthopaedic Surgeon:

• Hip surveillance and surgery
• Spinal deformity management
• Contracture correction
• Bone health management
• Coordination with seating team

Rehabilitation Physician:

• Medical oversight of rehabilitation
• Spasticity management
• Pain management
• Coordination of care
• Prescription authority

Assessment Process

Initial assessment components:

• Medical history and diagnosis
• Physical examination (range of motion, tone, posture)
• Current equipment evaluation
• Functional assessment
• Goals identification with patient/family
• Environmental considerations

Seating simulation:

• Trial of positioning options
• Angle adjustments
• Cushion comparisons
• Component testing
• Pressure mapping
• Photography documentation

Wheelchair seating is an area where strong physiological rationale often outruns high-level trial evidence. Examiners reward candidates who can state what is genuinely established versus what is consensus or extrapolation.

• Does seating prevent hip displacement in CP? No. Postural management and abduction positioning are widely used, but evidence that day seating prevents hip migration is weak; the Soo cohort and current surveillance practice treat hip displacement as a natural-history problem managed by radiographic surveillance and surgery, not by the chair. Seating accommodates, it does not protect the hip.
• The 32 mmHg "capillary closure" target. The figure derives from Landis's 1930 nailfold capillary measurements and is widely quoted, but real interface pressures over the ischium routinely exceed it without ulceration, and tissue tolerance varies with shear, time, perfusion and individual factors. Treat 32 mmHg as a teaching benchmark, not an absolute threshold; deep-tissue injury may begin at the muscle-bone interface independent of surface pressure.
• Air versus gel versus foam. The Brienza RCT shows specified skin-protection cushions beat plain foam, but it does not establish superiority of any one skin-protection technology. Cushion choice remains individualised to risk, posture, transfer technique and maintenance capacity rather than dictated by trial data.
• Standing programmes and 24-hour postural management. Biologically plausible for bone density, contracture and comfort, but supporting evidence is largely low-level; intensity and dosing remain uncertain.
• Timing of neuromuscular spinal fusion. Tension between operating early (better pulmonary reserve, more flexible curve) and delaying for skeletal growth; no consensus threshold, decisions are individualised around curve magnitude, FVC trajectory and pelvic obliquity.
• Powered versus manual mobility in young children. Early powered mobility may aid development and participation, but concerns about cost, safety and deconditioning mean practice varies widely.

Wheelchair seating need is driven by the global burden of cerebral palsy (roughly 2-3 per 1000 live births, the commonest cause of childhood physical disability), traumatic and non-traumatic spinal cord injury (global incidence on the order of 250,000-500,000 new cases per year), and progressive neuromuscular disease (Duchenne muscular dystrophy ~1 in 3500-5000 male births). Access to appropriate seating varies enormously between high-resource and limited-resource settings.

Side-by-Side Guidance

Registry and Surveillance Evidence

Population registers, rather than implant registries, drive practice here. The Swedish CPUP and the Victorian (Australian) CP registers generated the GMFCS-stratified hip-displacement data (Soo et al.) and the surveillance-reduces-surgery evidence (Hägglund et al.) that underpin worldwide hip surveillance programmes now adopted in the UK, Scandinavia, Australia and beyond.

High- vs Limited-Resource Practice

• High-resource settings: multidisciplinary seating clinics, pressure mapping, custom-moulded and powered tilt/recline systems, formal hip surveillance programmes, and third-party funding for complex assistive technology.
• Limited-resource settings: emphasis on appropriate, durable, locally maintainable manual wheelchairs (WHO model), simpler postural supports, and caregiver training; custom seating, pressure mapping and powered mobility are frequently unavailable, raising pressure injury and deformity risk. The clinical principles (neutral pelvis, pressure distribution, regular repositioning) remain universal even where the technology does not.

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3. Holmes KJ, Michael SM, Thorpe SL, Solomonidis SE. Management of scoliosis with special seating for the non-ambulant spastic cerebral palsy population. Clin Biomech. 2003;18(6):480-487.

4. Ágústsson A, Sveinsson Þ, Pope P, Rodby-Bousquet E. Preferred posture in lying and its association with scoliosis and windswept hips in adults with cerebral palsy. Disabil Rehabil. 2019;41(26):3198-3202.

5. National Pressure Ulcer Advisory Panel and European Pressure Ulcer Advisory Panel. Prevention and Treatment of Pressure Ulcers: Clinical Practice Guideline. National Pressure Ulcer Advisory Panel; 2014.

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10. Bushby K, Finkel R, Birnkrant DJ, et al. Diagnosis and management of Duchenne muscular dystrophy, part 2: implementation of multidisciplinary care. Lancet Neurol. 2010;9(2):177-189.

11. Soo B, Howard JJ, Boyd RN, et al. Hip displacement in cerebral palsy. J Bone Joint Surg Am. 2006;88(1):121-129.

12. Tsirikos AI, Lipton G, Chang WN, Dabney KW, Miller F. Surgical correction of scoliosis in pediatric patients with cerebral palsy using the unit rod instrumentation. Spine. 2008;33(10):1133-1140.

13. Hägglund G, Andersson S, Düppe H, Lauge-Pedersen H, Nordmark E, Westbom L. Prevention of severe contractures might replace multilevel surgery in cerebral palsy: results of a population-based health care programme and new techniques to reduce spasticity. J Pediatr Orthop B. 2005;14(4):269-273.

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