Tag: wheelchair seating

Postural stability and the effects of wheelchair cushions – Pelvic obliquity

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Abstract

Background: Pelvic obliquity (PO) is defined by a spinopelvic asymmetry in the frontal plane, the ASIS are not horizontally levelled. In The Netherlands 58% of the wheelchair users reports PO ranges from 2-4cm (4.5-9.1°).

Aim: Explore the causes, prevalence, and consequences of pelvic obliquity in the wheelchair using population

Method: Narrative literature review, with searches in PubMed, Google Scholar and references Results: 34 studies are included. There are different causes of PO:

  1. Suprapelvic obliquity results secondary to spinal pathology, such as scoliosis;
  2. Intrapelvic obliquity results secondary to architectural bony defects inherent in the hemipelvis;
  3. Infrapelvic obliquity results secondary to abduction or adduction hip contractures or limb length

PO can be categorized as functional (can be corrected) or as structural (cannot be corrected, only accommodated). The consequences of PO can be pain, scoliosis, lack of postural stability, and pressure injuries. Bolin et al. identified the wheelchair cushion as a factor in the development of PO, and advised the use of foam cushions for stability, but they did not investigate Vicair cushions. Inhouse research of Vicair found that the Vicair Adjuster O2 is highly suitable for accommodating a wide range of pelvic obliquity (4.57-9.17°) without the need to adjust the filling level.

Conclusion: There needs to be a balance between stability and pressure redistribution. By applying a compartmented air cell cushion, both stability and pressure redistribution can be optimized so pelvic obliquity can be prevented, corrected or accommodated.

 

1.  Background

Pelvic obliquity is an orthopedic condition defined by a spinopelvic asymmetry in the frontal plane,

i.e. the left and right anterior superior iliac spine (ASIS) are not horizontally level. Spinopelvic asymmetry often affects sitting balance and stance in ambulatory individuals (Ko et al., 2011). Pelvic obliquity can result in pain, pressure injuries and difficulties in maintaining sitting and standing postures. Resulting in reduced functional abilities (Porter et al., 2007).

Recent literature reports the acceptable range of maximal pelvic obliquity without surgical intervention to be (15 – 20°) in patients with cerebral palsy (CP), which is a 6.5 – 8.6cm height difference between the ASIS. There is currently no standardized classification for severity of pelvic obliquity (Yen et al., 2021). But the most common way to quantify pelvic obliquity is by determining the height difference between the left and right ASIS, see figure 1 (Shrader et al., 2018).

 

 

  1. ​Prevalence of pelvic obliquity

The prevalence of pelvic obliquity in the general population is largely unknown (Yen et al., 2021). Although there are many studies that report prevalence of pelvic obliquity in specific patients groups (i.e. 59.9% in patients with CP (Yen et al., 2021), there are no studies that report prevalence of pelvic obliquity in the overall adult wheelchair-using population.

Therefore, we performed an interview in a representative focus group of wheelchair-using adults in the Netherlands. Over a period of 2 weeks, fifty-five wheelchair users responded to this poll and 58% of them reported having been diagnosed with pelvic obliquity by either a doctor or therapist.

In the majority of cases pelvic obliquities ranged from 2 – 4cm (4.5 – 9.1°). Moharrami et all reported that in the normal population the pelvic obliquity angle ranges from 0.58 to 4.4°, indicating that the population we investigated has an above average pelvic obliquity angle (Moharrami et al., 2021). Relatively a lot wheelchair users in the Netherlands report pelvic obliquity, indicating the importance of investigating this topic and looking at adequate wheelchair cushion solutions.

The aim of this review is to explore both the causes, prevalence, and consequences of pelvic obliquity in the wheelchair using population.

 

2.  Methods

We designed a narrative literature review. To identify articles for the review, we conducted a literature search in PubMed and in Google Scholar in October of 2021 and updated this search in April 2023. The search terms were pelvic obliquity, wheelchair, cushion, seating system, correction, accommodation, weight distribution, scoliosis, health risks, pressure injuries and

variations of these search terms. The search was limited to studies published in English or Dutch. We did not specify limits on dates, study design, or the age of the participants. The references of found articles are also explored to look for relevant articles, those articles are also included in this review.

 

3.  Results

  • ​General description of the studies

A total of 34 studies was included in this review. The study designs were cross-sectional (retrospective) studies, retrospective studies, retrospective case-series, conference proceedings, case-control studies, prospective studies, cohort, longitudinal, literature reviews, editorial, experimental, and an educational tool (Table 2, appendix A). Studies were published between 1984 and 2023. A summary of study characteristics is shown in Table 2 (appendix A).

 

  • ​Causes of pelvic obliquity

Causes of pelvic obliquity can be classified using two systems. The first system classifies causes by location (Hamad et al., 2022):

  1. Suprapelvic obliquity results secondary to spinal pathology, such as scoliosis;
  2. Intrapelvic obliquity results secondary to architectural bony defects inherent in the hemipelvis;
  3. Infrapelvic obliquity results secondary to abduction or adduction hip contractures or limb length

It is often found that pelvic obliquity is not caused by only one location, but by a combination of both suprapelvic and infrapelvic causes (Hägglund, 2020).

The second system classifies causes by whether it is irrevocable or not.

  1. Structural pelvic obliquity, also referred to as fixed, cannot be corrected and can only be
  2. Functional pelvic obliquity, also referred to as flexible, is not yet irrevocable and can be (partially) corrected by postural support.

 

This difference is relevant for the user/therapist to make an educated decision about correcting or accommodating the pelvic obliquity with the seating system. Especially because a not corrected functional pelvic obliquity can lead to a structural pelvic obliquity, with all its consequences like pressure injuries, pain and deformities (Porter et al., 2007).

 

Hasler et al. described a test which can be performed to determine the origin of the pelvic obliquity: The patient is placed in a prone position on the edge of a bed with only the torso and head on the bed and the hips flexed. The hips are then manipulated left to right and the scoliotic curve is re-examined. If the pelvic obliquity can be corrected by this maneuver, then it is secondary to an infrapelvic pathology. If the pelvic obliquity does not reduce, then it is secondary to a suprapelvic pathology (Hasler et al., 2020).

However, in clinical practice the MAT assessment is used more often. This test is performed in three stages: postural assessment in existing seating system, assessment in supine position, assessment while seated. Supine assessment provides gravity-eliminated information. It should be conducted on a padded firm surface such as a plinth as it is difficult to assess spinal curves on soft support surfaces, (e.g. bedding) or to manipulate the pelvis and trunk positions when

assessing joint flexibility and skeletal alignment. The sitting phase of the MAT aims to evaluate the effect of gravity on posture, and trunk flexibility. By comparing joint flexibility recorded in supine assessment, with the posture presentation in sitting assessment, the clinician can then manually manipulate the trunk position and/or place supports under the pelvis to improve skeletal alignment. This is referred as simulation task which forms the basis of seating intervention plan (Lange & Minkel, 2017).

 

Hereafter the two main causes of pelvic obliquity – suprapelvic and infrapelvic obliquity – will be described.

 

Vialle et al. had an explanatory figure in their article ‘neuromuscular scoliosis’. The figure shows that if pelvic obliquity results from a pre-existing scoliosis the muscles connecting the trunk and pelvis can asymmetrically retract (fig A). Figure B and C show that hip posture asymmetry causes retraction, usually in adduction, flexion and internal rotation, predominating on one hip; this asymmetry of retraction induces pelvic malpositioning (Vialle et al., 2013).

 

 

3.2.1 ​Suprapelvic – scoliosis

Scoliosis is an abnormal lateral (sideways) curving of the spine. Scoliosis can be both a cause and a consequence of pelvic obliquity. In the case of suprapelvic obliquity, pelvic obliquity is secondary to the spinal deformity in which scoliosis may drive the pelvis into an asymmetrical position(Chan et al., 2019).

A higher prevalence of pelvic obliquity is observed in patients with lumbar curves than in thoracic curves(Banno et al., 2020). This study was performed in ambulant Adolescent Idiopathic Scoliosis (AIS) patients, but is still relevant for wheelchair users with scoliosis since it shows the relation between scoliosis and pelvic obliquity.

There are different types of scoliosis:

  1. Idiopathic scoliosis is a scoliosis without a specific cause, the diagnosis is made by exclusion, AIS is an example of this type. AIS affects 2% of the adult population (Ogilvie, 2010).
  2. Congenital scoliosis results from embryological malformation of one or more
  3. Degenerative scoliosis is associated with progressive and asymmetric degeneration of the disc, facet joints, and other structural spinal elements. This type can either be the cause of pelvic obliquity ((Radcliff et al., 2013) or be secondary to pelvic obliquity (Kotwal et al., 2011).
  4. Neuromuscular scoliosis is secondary to neurological or muscular diseases, such as Cerebral Palsy (CP), SCI, muscular dystrophies (Scoliosis – Symptoms, Diagnosis and Treatment, d.; Vialle et al., 2013).
  5. Traumatic scoliosis, this type of scoliosis develops due to an injury or trauma sustained by the

 

In case of suprapelvic obliquity caused by scoliosis interventions designed to reduce scoliotic curves and release tissue contractures can level the pelvis and restore proper alignment of the spine and sacrum (Yen et al., 2021). Therefor it is also important to look at the cause of the pelvic obliquity and cause of the scoliosis.

 

Scoliosis is a common problem in lots of diseases, which also increases the incidence of pelvic obliquity. For neuromuscular scoliosis Vialle et al investigated the prevalence for specific diseases:

 

 

Weigl even reports that 61-77% of the non-ambulatory patients with CP have a scoliosis (Weighl, 2019).

 

  • ​Infrapelvic

Pelvic obliquity can also be caused by hip problems or limb length inequalities, these are infrapelvic causes.

Asymmetrical limited hip flexion (< 90°) is caused by a loss of range of motion due to contractures

 

in the hip flexors (Ágústsson et al., 2017). This increases the chance of getting pelvic obliquity (Odds ratio of 2.6 in CP patients) (Ágústsson et al., 2017). If asymmetrical limited hip flexion is the cause of the pelvic obliquity this is called infrapelvic obliquity. Be aware of the fact that a

compensating lateral spinal curvature can be present (Porter et al., 2007), this is due to the fact that the ipsilateral side of the pelvis will go up and in a forward direction, directing the trunk to the contralateral side (Pope, 2006).

Other causes of infrapelvic obliquity in non-ambulatory wheelchair users is dislocation of the hip (Hägglund, 2020; Letts et al., 1984) Letts described how a dislocated hip can lead to pelvic obliquity, it starts with a restricted range of hip abduction, the hip can no longer be fully move to the side. This is associated with a hip flexion contracture, the hip cannot be fully extended, which leads to subluxation of the hip. Due to the subluxation of the hip pelvic obliquity occurs. When the subluxation progresses in a complete dislocation of the hip, the severity of the pelvic obliquity usually increases (Letts et al., 1984).

Windswept hip distortion can also cause infrapelvic obliquity. The windswept hip deformity/ distortion comprises abduction and external rotation of one hip, with the opposite hip in adduction and internal rotation (Hägglund et al., 2016; Zwick, 2014). The odds of it occurring in patients with CP are 2.6 (Ágústsson et al., 2017).

 

 

 

3.2.3​ Intra pelvic obliquity

Although the two main causes of pelvic obliquity are infra and supra pelvic obliquity, intra pelvic causes can also be the reason of pelvic obliquity in wheelchair users. Usually they are caused by developmental problems of the hip or pelvis. Such as Developmental Dysplasia of the Hip (DDH) (Yu et al., 2021; Zhang et al., 2015). Intra pelvic obliquity can sometimes be reduced by a Total Hip Arthroplasty (THA) (Zhang et al., 2015). The pelvic bone is flexible and plastic, which makes it possible that intra pelvic obliquity angles change over time (Yu et al., 2021; Zhang et al., 2015).

 

  • ​Functional pelvic obliquity

Functional pelvic obliquity can occur due to a combination of insufficient support from the seating system (e.g. slingback foldable wheelchair) and muscle weakness (Bolin et al., 2000; Medhat & Redford, 1985). Some technical causes of pelvic obliquity may be that the seat cushion does not

 

provide sufficient support, the wheelchair too wide, arm supports too high or too low or that the person has not been correctly positioned in the wheelchair (Chantry & Crombie, 2018).

These factors leads to leaning, since the patient does not have the support to sit upright and leads to functional scoliosis and pelvic obliquity. If a patient remains in this unsupported condition for a long period of time, the functional deformations may become irreversible and with that will become a structural deformation (Medhat & Redford, 1985).

 

  • ​Structural pelvic obliquity

As mentioned before, structural pelvic obliquity cannot be corrected, but only accommodated. The main cause of structural pelvic obliquity is scoliosis. This can be due to the fact that no intervention took place in the early stages of spinal deformity when there were no contractures and scoliosis and pelvic obliquity could be corrected by ensuring stability and postural support (Engström, 1993). Lee et al. found that a combination of surgical procedures can improve the pelvic obliquity in most patients. In patients with infra pelvic obliquity the surgeries involved fasciotomy of specific muscles and stabilization of the hip. In patients with supra pelvic obliquity spinal fusion was usually necessary (Lee et al., 1997).

 

  • ​Consequences of pelvic obliquity

Yu et al. found that the sacroiliac joint has a considerable compensatory ability to ensure coronal balance (lateral alignment of the spine) in patients with pelvic obliquity due to developmental dysplasia of the hip. They also referenced an article that found the same in patients with pelvic obliquity due to scoliosis. Indicating that in some patients the pelvic obliquity has minimal consequences for coronal balance. Yu et al. classified patients in 3 groups (figure 4):

  1. Type 1: the pelvic obliquity is small and can be compensated by the sacroiliac joint, without the spine compensating (no scoliosis) (Figure 4 a).
  2. Type 2a: the pelvic obliquity is aggravated compared to type 1, and the sacroiliac joint alone is not enough to fully The spine participates in the compensation of the coronal balance, which manifests as a long gentle c-shaped curve (Figure 4 b)
  3. Type 2b: the pelvic obliquity is severe, the sacroiliac joint is decompensated (reverse compensation, causing heavy obliquity of the sacrum), and the sacrum becomes part of the compensatory curve of the lumbosacral curve. It manifests as a sharp short curve in the lumbosacral area (figure 4 c). (Yu et al., 2021).

 

 

 

 

 

Pelvic obliquity can be caused by a scoliosis, but as a consequence of pelvic obliquity a scoliosis can also develop. Since pelvic obliquity causes a malalignment of the spinal column, lateral spinal curvature is needed to compensate for the asymmetry caused by pelvic obliquity (Ágústsson et al., 2017) . When spinal deformities such as scoliosis occur in an adult non-ambulatory wheelchair user, this can be caused by a lack of postural stability and pelvic obliquity due to insufficient support from the support surface of the wheelchair (Bolin et al., 2000; Engström, 1993).

This scoliosis is a natural response to pelvic obliquity and is not necessarily structural and can be reduced when the wheelchair user is seated on a firm flat surface when assessed for pelvic obliquity. However, when the wheelchair user has a pelvic obliquity and concurrent scoliosis for a

prolonged time without relief, these spinal deformations can become structural (Bolin et al., 2000; Engström, 1993). Hence why treatment of non-structural deformations is important and why it’s important to examine what the cause of the pelvic obliquity is.

 

  • ​Sitting balance

A functional and ergonomic sitting position is necessary to attain a high level of independence and to prevent secondary complications (Bolin et al., 2000). Pelvic asymmetry and scoliosis can negatively affect postural stability during sitting, and postural instability increases in participants with both pelvic asymmetry and scoliosis. More than pelvic asymmetry or scoliosis alone (Jung et al., 2015).

 

A lack of postural stability can cause pressure injuries and advance deformations in the spine (Jung et al., 2015). Furthermore, a lack of postural stability can lead to issues regarding safe transfers, wheelchair skills, physical strain during wheelchair propulsion, activities of daily living (ADL’s), pain, and spasticity (Bolin et al., 2000).

It can also lead to shoulder injuries, such as rotator cuff disorders, which itself can greatly limit the independence, ADL’s, and participation in society (Dyson-Hudson & Kirshblum, 2004; Sinnott et al., 2000). Stabile sitting is related to better overall quality of life and physical function (Bartnicki et al., 2012).

 

 

Pelvic obliquity not only causes scoliosis and postural instability it can also lead to problems with pressure distribution and pressure injuries. A study by Jung et al. on individuals with either pelvic obliquity, scoliosis, or both, found that maximum forces and peak pressures increased on the right side when performing lateral pelvic tilting during sitting. While pressure distribution decreased

on the right side (Jung et al., 2015). This has influence on the overall pressure distribution, the pressure is distributed asymmetrical. Jung et al. also saw in their study that the maximum forces and peak pressure of individuals with pelvic asymmetry are asymmetrically distributed (Jung et al., 2015). Another study in patients with paralytic scoliosis showed a mean value of 86% weight supported on one side (Larsson et al., 2002). Uneven weight bearing does not only significantly increase the risk of pressure injuries on the lower side of the pelvis (Hägglund, 2020; Larsson et al., 2002; Tsai et al., 2023) but can also lead to painful sitting for patients with intact sensation (Larsson et al., 2002).

 

A study by Patel et al. found that a greater degrees of thoracic scoliosis and pelvic obliquity were correlated with greater average and peak pressures and larger areas of high pressure (38-70 mmHg) in patients with Spina Bifida (Patel et al., 2011).

The spinal deformity and pelvic obliquity alters the sitting balance and puts individuals at risk for uneven pressure loading on insensate skin and resultant pressure injuries (Patel et al., 2011).

 

Ouellet et al. observed that in patients with pelvic obliquity and scoliosis the overall pressure distribution from anterior/posterior and right/left improved after surgery (Ouellet et al., 2009). Moreau found a similar pattern, the ratio of left/right pressure correlated with improvement in pelvic obliquity after surgery (Moreau et al., 2002).

Majd et al. found that the patients who developed pressure injuries had a significant greater scoliosis and pelvic obliquity angle than those patients without pressure injuries (Majd et al., 1997). And Lefèvre et al. found that scoliosis and pelvic obliquity are related with a higher chance of recurrence of pressure ulcers (Lefèvre et al., 2018). In line with this finding are the results

of Drummond et al.: they investigated the relation between asymmetric pressure loading due to pelvic obliquity and/or scoliosis already in 1985. They found that 9/10 patients with pressure injuries showed asymmetrical loading due to pelvic obliquity, and 8 of them also had scoliosis

 

(Drummond et al., 1985).

Nagata et al. show that when pelvic obliquity is simulated the shear in a reclining chair increases (Nagata et al., 2021). Increase shear is another risk factor for the development of pressure injuries. Indicating the importance of an appropriate wheelchair cushion to accommodate or correct the pelvic obliquity when possible.

 

1.  Discussion

The aim of this review was to explore both the causes, prevalence, and consequences of pelvic obliquity in the wheelchair using population. The Dutch survey revealed that 58% of the wheelchair users has pelvic obliquity. Scoliosis is a common factor associated with pelvic obliquity and can

be both a cause and a consequence of pelvic obliquity in the wheelchair using population. The sequence in which pelvic obliquity and scoliosis occurs is dependent on the location of the cause of pelvic obliquity. In the case of supra-pelvic obliquity, pelvic obliquity is secondary to scoliosis (Chan et al., 2019). In other words, an individual has a pre-existing scoliosis due to i.e. Cerebral Palsy, Spina Bifida, or Idiopathic Adolescent Scoliosis.

In the case of infra-pelvic obliquity, pelvic obliquity can occur due i.e. to poor sitting balance resulting from insufficient support from the support surface of the wheelchair leading to pelvic obliquity. The lack of support can lead to leaning and other compensatory behaviors which can lead to a compensatory scoliosis (Bolin et al., 2000; Engström, 1993). These spinal deformations start out as functional, but if the wheelchair user has a pelvic obliquity and concurrent scoliosis for a prolonged time without relief, these spinal deformations can become structural(Bolin et al., 2000; Engström, 1993).

 

10 studies mentioned the risk of pelvic obliquity on pressure distribution and pressure injuries. Only Drummond reported that 90% of their patients with a pressure injury had pelvic obliquity and 80% had a scoliosis. However, none of these studies reported by how much pressure injury risk was increased.. Although this information is missing, other research to the consequences of pelvic obliquity (asymmetrical loading) do indicate the importance of a wheelchair cushion suitable for accommodating and if possible correcting, the pelvic obliquity to potentially reduce the pressure injury risk.

 

Although there is a lot of literature on pelvic obliquity in patients with Cerebral Palsy (CP), Adolescent Idiopathic Scoliosis (AIS) and Spinal Cord Injuries (SCI), there is very little research on pelvic obliquity in the general wheelchair using population. But we also found literature regarding neuromuscular diseases, poliomyelitis, developmental dysplasia of the hip and myelomeningocele, since all these groups combined form a great part of the wheelchair using population, we can conclude that the findings from this review can be used for the majority of the total wheelchair using population.

 

  • The role of wheelchair cushions in patients with pelvic obliquity

Furthermore, the study by Bolin et al. was the only study that identified wheelchair cushions as a factor in the development of functional pelvic obliquity and the consequences of a concurrent lack of postural stability and tackled this problem by deploying more stable foam cushions that corrected their pelvic obliquities (Bolin et al., 2000). However, the risk of developing pressure injuries could be increased by the use of a foam cushion. From other research we know that foam cushions may increase the risk of pressure injuries (Shi et al., 2021), luckily Vicair found a

solution for this; Viscose air; Wheelchair cushions that come close to the stability of foam cushions because the separate tetraëder shaped SmartCells acts like a viscous fluid, but provide the

 

pressure distribution characteristics of air cell based wheelchair cushions because they are filled with air. Furthermore, the ability to make changes to the filling grade allows for accommodation and correction of pelvic obliquity. Accommodation means that the cushion adapts to the pressure and offers even pressure distribution without forcing the user into a different position. Correction means that the cushion supports the pelvis to achieve a more neutral posture.

 

In house research of Vicair investigated the effect of Vicair cushions on different degrees of pelvic obliquity. To evaluate the properties of the cushions, pressure distribution during loading in various angles of pelvic obliquity (4.57 – 9.17°) is observed. The standard filling grade of the cushions is used.

The Vicair Adjuster O2 is highly suitable for accommodating a wide range of pelvic obliquity (4.57 – 9.17°, which is a height difference at the ASIS of 2-4cm) without the need to adjust the filling level. The cushion adapts to the user and the pressure is evenly distributed over the seating area. The Vicair Vector O2 is capable of providing corrective pressure in case of pelvic obliquity without causing excessive pressure in the high-risk zones.

 

2.  Conclusion

According to a survey pelvic obliquity is common (58%) in the general wheelchair population. And the consequences of pelvic obliquity can be big, namely: scoliosis, lack of stability and pressure injuries. However, little evidence exists on the cause of pelvic obliquity and how pelvic obliquity can be corrected or accommodated in this population. Research suggests that a functional pelvic obliquity (caused by a lack of postural support) can be corrected by using a wheelchair cushion that improves postural stability. A foam wheelchair cushion is more stable than an interconnected air cell-based wheelchair cushion (De Groot, 2021). However, a foam cushion is not very adaptable. An interconnected air cell-based wheelchair cushion follows the contour of the user, giving optimal pressure distribution. However, this comes at the cost of support from the support surface and stability. There needs to be a balance between stability and pressure redistribution.

By applying a compartmented air cell cushion, both stability and pressure redistribution can be optimized so pelvic obliquity can be prevented, corrected or accommodated.

 

 

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Postural stability and the effects of wheelchair cushions

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Abstract

Background: Postural stability refers to the continuous process of postural changes during sitting.

The capacity to maintain postural stability in sitting position is a prerequisite to perform activities of daily living (ADLs), reduce risk of shoulder injury, pressure injuries and falling, but also social functioning, satisfaction with equipment, and thus quality of life. Deficits in postural stability can severely limit performance in these aspects of life.

There are different ways to measure postural stability, namely by center of pressure, reach test, wheelchair skills test, among others. And 2 ways to measure stability of a cushion itself, namely horizontal stiffness test and the lateral stability tilt test.

Aim: Determine what factors influence postural stability, more specific of the wheelchair cushion,

and how this data is relevant for Vicair wheelchair cushions.

Method: Literature review, search in PubMed, Google Scholar and references in May 2023.

Results: 25 studies are included.

There are several contributing factors to obtaining and retaining postural stability in a sitting position, namely trunk strength, foot support, large base of support, anterior pelvic tilt, thigh support, back support and wheelchair set-up. Anterior pelvic tilt, thigh support, and a stable sitting surface can all be achieved using an appropriate wheelchair cushion.

Stability of the wheelchair user can be compromised by the cushions ability to resist medial-lateral or anterior-posterior pelvic rotations caused by shifting center of mass. The Jay 2, ROHO High Profile and Varilite Evolution could not create a stable base to perform reach. Vreede found that a compartmented air cell cushion could provide a stable base to perform reach and ADL tasks (Vreede, 2018).

Conclusion: Selection of an adequate wheelchair cushion is of utmost importance to ensure a satisfactory quality of life of wheelchair users. Increase in of postural stability in a sitting position can be obtained by using a compartmented air cell cushion.

 

1.  Background

  • ​What is postural stability?

Postural stability is the ability to keep or return the center of body mass over the base of support in a position or during changes in position. It is a complex process involving coordinated actions of biomechanical, sensory, motor and central nervous system components (Horak, 1990).

Sitting balance is believed necessary in performing functional activities from a seated position. Several prognostic studies have shown that seating balance is a valid predictor for functional outcomes, such as activities of daily living (ADLs) in patients with brain injury or stroke (Black et al., 2009; Kwakkel et al., 1996; Sandin & Smith, 1990; Wade et al., 1983; Wade & Langton Hewer, 1987). Tidemann found that sitting balance is a relevant factor to define functional sitting position. They found that sitting balance is assumed to be essential for obtaining independence in other vital functions such as reaching, sit-to-stand, and sitting down. Balance is therefore relevant to consider in particular with regards to reaching tasks that might challenge the users’ postural stability (Tidemann et al., 2019).

 

Impact of postural stability:

 

  1. Activities of daily living (ADLs)

The wheelchair and/or seating system should enable individuals to perform the activities of daily living (ADLs) that are important to them with minimal to no assistance and with the least amount of energy expenditure. Types of activities can include transfers, personal needs (e.g., bathing, toileting), working, preparing meals, cleaning, and shopping.

The capacity to maintain postural stability in a sitting position is a prerequisite to perform ADLs and deficits in postural stability can severely limit task performance (Dean, 1997; Riley et al., 1995). Adequate sitting stability is positively correlated with performance of ADL tasks (Chen et al., 2003). A lack of postural stability can lead to issues regarding safe transfers, wheelchair skills, physical strain during wheelchair propulsion, ADL, pain, and spasticity (Bolin et al., 2000).

In 2014, Gao et al. found that individuals with a faster reaction on the sitting balance test had better mobility scores in the functional mobility assessment. Similar results were found for participants who could lean more and had better directional control. In ADLs, being able to shift the body’s center of mass controllably in all directions is important and therefore relevant for daily functioning (Gao et al., 2015).

 

  1. Propulsion and shoulder injury

Lack of postural stability due to impaired abdominal- thoracic musculature has been linked to increased susceptibility to shoulder pain and shoulder injury. Poor seating posture due to improper wheelchair seat position and configuration can further increase this susceptibility (Dyson-Hudson & Kirshblum, 2004). Wheelchair cushions can help in correcting posture. Another study, Sinnott et al, found a high correlation between the prevalence of rotator cuff disorders and level of injury in individuals with SCI. This study also showed a correlation between shoulder injury and decreased trunk control and pelvic stability. 72.7% of individuals with poor postural control were diagnosed with bilateral rotator cuff disorders. This study also reported that more than 70% of all individuals with SCI experience shoulder pain (Sinnott et al., 2000). Prevalence of pain and rotator cuff tears (63%) is higher after paraplegia than age-matched able-bodied controls (15%), highlighting the importance of trunk stability (Akbar et al., 2010).

Seated postural stability also strongly contributes to propulsion and together with strength- generating capabilities of the shoulder, it explains 71.3% of variance observed in propulsion (Gagnon et al., 2016). Triolo et al. found similar results in their study: ‘Stabilizing the pelvis and trunk with low levels of continuous electrical stimulation to the lumbar trunk and hip extensors can positively impact the mechanics of manual wheelchair propulsion and reduce both perceived and physical measures of effort’ (Triolo et al., 2013).

Dyson-Hudson & Sinnot also emphasize the great impact that shoulder injuries can have on peoples independence, ADL’s, and participation in society, which also brings us to the impact on quality of life (Dyson-Hudson & Kirshblum, 2004; Sinnott et al., 2000).

 

  1. Quality of life

Postural stability is not only important for improvement in functional outcomes such as reach and the ability to perform ADLs, but it is also important for social functioning and satisfaction with the equipment and therefore for quality of life. One of the given reasons for the improvement could be the fact that participants had less difficulty propelling their new wheelchair (Trefler et al., 2004).

 

  1. Falling

Postural instability is a common problem for wheelchair users that can result in increased risk of falling (Okunribido, 2013; Poojary-Mazzotta, 2016). Okunribido et al. found that during wheelchair transfers the risk of the occupant falling forward and out of the wheelchair is higher when they are sat on a thick soft cushion (100mm castellated Propad HOMEPAD low profile), compared to a hard regular cushion (50mm basic polyurethane (flat foam) high-density), particularly when the feet are unsupported. The risk of falling is increased when the occupant is prone to slouch forward in the wheelchair, due to their medical condition (Okunribido, 2013).

 

  1. Pressure injuries & other

A lack of postural stability can cause pressure injuries and advance deformations in the spine (Jung et al., 2015). The seated posture affects how loads are redistributed. Postural instability can induce asymmetric loading on for instance the ischial tuberosities. A slouched, kyphotic posture creates extra pressure at the sacrum and coccyx while seated. Body posture and positioning have a direct relationship to loads on specific body sites, which is why posture and stability must be considered when devising pressure ulcer prevention strategies (Sprigle & Sonenblum, 2011).

 

Furthermore, a lack of postural stability can lead to issues regarding safe transfers, wheelchair skills, pain, and spasticity (Bolin et al., 2000).

 

  • ​Measuring postural stability:
  1. COP

There are several instruments that can be used to assess postural stability in a sitting position. One frequently used measure to assess stability is center of pressure (COP). Test-retest reliability is moderate to excellent for COP. This test-retest reliability indicates that COP measures of multidirectional seated postural stability may be useful as a clinical measure and similar results have been found in a study focusing on stroke patients. However, COP is not an effective instrument to determine sway, which can occur during quiet sitting (Kerr & Eng, 2002; Näf et al., 2020). Quiet sitting is not sitting completely motionless, usually there is some movement, called sway.

Everyone experiences postural sway to some degree. But in some cases, created postural sway can be an indication of poor balance and coordination.

 

 

Figure 1 (right). Centre of Pressure measurements, measured with a pressure plate underneath the buttock and feet of a hemiplegic wheelchair user (T. Sato & Nabeya, 2021).

 Figure 2 (left). Start and end position of the seated reach test. Start position is the stippled gray figure, maximum reach in the forward (dark gray), leftward (light gray) and backward (white) direction. Rightward reach was also tested but is not illustrated (Field-Fote & Ray, 2010).

 

  1. Reach tests

Another method to measure stability/dynamic sitting is the seated reach test (SRT). The SRT is a test of maximal reach distance forwards, leftwards, rightwards and backwards (see figure 2). Field-Fote et al. demonstrated that the seated reach test has a good to excellent test-retest reliability and a significant correlation with COP. Similar test-retest reliability results were found in a study by Gao et al., indicating that the seated reach test is a valid and reliable method to measure stability (Field-Fote & Ray, 2010; Gao et al., 2015; Sprigle et al., 2003) .

 

  1. WST

A third comprehensive method to assess postural stability while being seated (May et al., 2003), is a wheelchair skills test (WST) including 30 functional tasks that wheelchair users encounter in daily living. These tasks are scored ranging from 0 (fail) to 3 (advanced pass) on a score form (figure 5 in appendix C). Test-retest and inter-rater reliability for all tasks included in the WST are excellent (May et al., 2003). Available via: https://wheelchairskillsprogram.ca/en/skills-manual- forms/

 

  1. Other methods

Some less used methods to assess postural stability are the Berg Balance Scale (BBS) which evaluates postural control with static and dynamic tasks in 14 sections (figure 6 in appendix C) (Wong, 2014), the Posture And Postural Ability Scale (PPAS) which evaluates posture quantitively and qualitatively (figure 7 in appendix C)(Rodby-Bousquet et al., 2014), the Function in Sitting Test (FIST) which evaluates the level of functionality in sitting with 14 tasks (figure 8 in appendix C) (Abou et al., 2020), and the Trunk Control Test (TCT) which evaluates the control that the subject has over their trunk. However, some of these (BBS, PPAS, TCT & FIST) tests are less reliable since they are dependent on the level of skill and experience of the therapist (Reguera-García et al., 2020). Abou et al. found that the FIST is still a reliable and valid test with an excellent test- retest reliability, and the FIST correlates with the lateral modified Functional Reach Test (Abou et al., 2020).

 

Frechette et al. described how smartphones could be used as a postural control assessment in wheelchair users. Their pilot study illustrated that smartphone-based accelerometry may be able to provide a valid and reliable assessment of seated postural control and has the ability to distinguish between those with and without impaired postural control (Frechette et al., 2020).

 

Santamaria et al. validated the seated postural & reaching control test in children with cerebral palsy (CP), it is a reliable and valid test for therapists to objectively examine and quantify seated postural and reaching control (Santamaria et al., 2020).

 

Sato developed the Shoulder Shifting Test (SST) for individuals with an SCI and difficulty raising their arms. They found that the SST was compatible with the SRT, and the sitting balance of more individuals with SCI could be assessed by the combination of these tests (H. Sato et al., 2022).

In 2021 T. Sato studied the relation between reach distance and COP in patients with hemiplegia. They asked patients to reach maximal toward the front (a), toward the nonparetic side (b), and toward the paretic side (c) (see figure 4). They found that depending on the trunk function there is a moderately strong to strong or lower correlation (T. Sato & Nabeya, 2021).

 

 

Figure 3. Multidirectional reach items (T. Sato & Nabeya, 2021). With the arm of the non-affected side is reached to that side (a), followed by a

frontal reach (a) and a reach to the affected side (c).

  1. Cushion tests: Besides testing the stability of the wheelchair user it is also possible to test the stability of the cushion itself, these tests are described in ISO 16840, namely the horizontal stiffness test & tilt test. A short description of these tests can be found in the table below (table 1) and a visual overview in figure 5.

 

 

 

 

The aims of this review are:

  1. To determine what factors influence postural stability,
  2. To determine what determining factors in a wheelchair cushion are to obtain optimal postural stability,
  3. To determine how this data is relevant for Vicair wheelchair cushions.

 

1.  Methods

We designed a literature review. To identify articles for the review, we conducted a literature search in PubMed and in Google Scholar in February of 2021. And updated the search in May 2023. The search terms were reach, seated functional reach, wheelchair, cushion, support surface, daily functioning, ADL, thigh support, propulsion, and variations of these search terms. Furthermore, we consulted the references of the literature for relevant articles. The search was limited to studies published in English or Dutch. We did not specify limits on dates, study design, or the age of the participants.

 

2.  Results

  • ​General description of the studies

A total of 25 studies was included in this review. The study designs were randomized controlled trials/intervention studies, case studies, case-control studies, repeated measures studies, and cross-sectional group studies, among others (Flowdiagram 1, Appendix A & Table 2, Appendix B). All studies were published between 1986 and 2022. A summary of study characteristics is shown in Table 2 (Appendix B).

 

  • ​Factors influencing postural stability

There are several contributing factors to obtaining and retaining stability in a sitting position, both intrinsic factors and external factors.

 

  1. Trunk strength

One of the most known contributing factors for stability in a sitting position is trunk strength. Less affected trunk extension and flexion strength is statistically significantly associated with higher levels of reach (Gabison et al., 2014).

 

  1. Foot support

In 1986, a wheelchair basketball player with bilateral above the knee amputation pointed out that wearing his prostheses allowed him to lean farther forward. This observation led to speculation that the lower limbs, or their prosthetic replacements, might contribute to sitting balance in forward-

 

reaching tasks by enlarging the base of support. This led to a study to determine the extent of the contribution of one or both legs on sitting balance. The study confirmed the observation of the basketball player (Chari & Kirby, 1986). The results of that study were later supported by a study by Janssen-Potter et al. who assessed the effect of the footrest on sitting balance in paraplegic subjects and healthy individuals. Although healthy participants did show a decrease in reach and displacement of the center of pressure (COP) while seated in a chair with an elastic foot support, these results were not seen in subjects with SCI. The elastic foot support does have influence on how reach is performed by subjects with an SCI , indicating that a solid foot support contributed to postural stability (Y. J. Janssen-Potten et al., 2002).

 

  1. Anterior pelvic tilt

Another contributing factor to obtain stability in a sitting position is anterior pelvic tilt. This was demonstrated by a study by Amos et al. (Amos et al., 2001). They measured functional reach while seated in a wheelchair using goal-directed tasks since this produces a higher quality of movement and is more concrete and purposeful than a rote (mechanical or habitual repetition of something to be learned) reaching task. Participants sitting with forward pelvic rotation had a significantly greater forward functional reach compared to participants sitting in a wheelchair with a sling seat that allowed backward pelvic tilt. Besides an increase in functional reach, forward pelvic tilt also allows for less head-forward positioning and less shoulder protraction and a more upright trunk position (Amos et al., 2001; Hastings et al., 2003). Rice et al. found in their pilot that anterior tilt in a power wheelchair is also helpful for vertical reach, and with that participants found anterior tilt helpful in performance of reaching tasks (Rice et al., 2019).

 

  1. Thigh support

Thigh support is also considered a contributing factor to the increase of stability in a sitting position. A study with 12 healthy elderly volunteers showed no statistically significant difference between percentage of thigh support and duration of reaching task (Dean et al., 1999). However, another study that followed the same protocol as Dean et al. found that there was a significant effect of amount of thigh support on velocity and extent of reach during a reaching task in the participants with spinal cord injury (SCI) indicating that thigh support is a contributing factor to stability in a sitting position in disabled individuals. Passive mechanical participation of the paralyzed body is probably reduced when the thigh support is reduced (Ilha et al., 2020).

 

  1. Back support

A factor contributing to static postural stability that is often overlooked, is back support. In 2020, a study was performed where the wheelchair’s back support of 50 participants with chronic SCI was removed and replaced with a solid back to assess whether a solid back would improve postural alignment, increase forward upward reach, promote respiratory function and facilitate mobility as compared with an upholstery back. Posterior pelvic tilt was significantly reduced by using a solid back. Furthermore, all functional outcome measures were improved when using the solid back support. However, statistical significance was not achieved due to the low number of participants. The increase in vertical forward reach was noted as a clinically significant difference as it is double the minimal detectable change (Presperin Pedersen et al., 2020).

A study by Ukita et al. also underlined the importance of back support shape to contribute to postural stability. However, in this study greater postural stability was achieved by pelvic support (Ukita et al., 2020).

 

  1. Wheelchair set up

Several studies have investigated the effect of wheelchair configuration or seating systems on reach and upper extremity functional tasks. These studies found results differed depending on the task and the configuration used in the study (Aissaoui et al., 2001; Amos et al., 2001; Bolin et al., 2000; Curtis, 1995; Hastings et al., 2003; Y. J. Janssen-Potten et al., 2002; Y. J. M. Janssen- Potten et al., 2000).

 

Hastings et al found that persons with complete SCIs exhibited a more erect posture and a greater vertical reach ability while sitting in a wheelchair with posterior seat inclination, low back support height, and acute seat-to back angle (clinically referred to as ‘‘squeeze’’) compared with standard wheelchair configurations (Hastings et al., 2003). Bolin, Bodin, and Kreuter compared changes in seating and wheelchair configuration of 4 wheelchair users with C5-C6 tetraplegia on 8 different variables: balance, transfers, wheelchair propulsion, wheelchair skills, physical strain, spasticity, respiration, and perceived changes by the subjects. They found that the variables tested were affected by the sitting position in an individual manner and that not 1 standard solution worked for all (Bolin et al., 2000). The results of these studies were corroborated by Sprigle et al, who concluded that individuals may perform better with a particular seating system but that no single seating system is best for all people (Sprigle et al., 2007).

 

  1. Other factors

Other factors that can positively influence postural stability, seated balance, or reach: Exercise (Rose Lee-Hauser et al., 2021), passive trunk orthosis (Rao & Hasan, 2021), virtual reality training in patients with SCI (Nair et al., 2022), epidural electro stimulation in patients with severe thoracic SCI’s (Gill et al., 2020), exoskeleton walking training (Tsai et al., 2021).

 

  • ​Wheelchair cushion effects on postural stability

Functional reach can be increased by individually configured wheelchairs and seat cushions, according to Brienza (Brienza et al., 2010). The seat cushion, as the base of support for the wheelchair user, affects postural stability by resisting moments when the users’ center of mass (CoM) is displaced. For example; users’ center of mass shifts as they lean during a reach activity or when users encounter a sloped surface. Stability of the wheelchair user can be compromised by the cushions ability to resist medial-lateral or anterior-posterior pelvic rotations caused by shifting center of mass (Delazio et al., 2019).

 

In 2001, Aissaoui et al. designed a study with the aim to examine the effect of seat cushions on postural stability in sitting during a controlled reaching task performed by individuals with paraplegia. They used an interconnected air cell cushion (3-inch air-flotation ROHO), a contoured foam cushion (3-inch polyurethane HR45, ISCUS) and a flat foam cushion (2-inch polyurethane HR35) . They included 9 wheelchair users with paraplegia by SCI. During the reaching task, the pressure distribution at the body-seat interface was recorded by a force-sensor array. The maximal covered distance (MCD) by the center of pressure (COP), the maximal velocity (MV) of the COP, as well as the surface area underneath the curve defined by the velocity-distance relationship were computed. When a contoured foam cushion is used, the COP covers a larger distance with higher speeds compared to the interconnected air cell cushion or the flat foam cushion. They found that paraplegic subjects were able to increase both the distance covered and the velocity of the COP when a generic contoured cushion was used during reaching. The ability of the COP to cover a large distance with high velocity appears to be linked to the increase in postural stability during reaching (Aissaoui et al., 2001).

 

Sprigle et al. reported that subjects exhibited greater reach when sitting with a pelvis positioned on a stable base on which upper extremity and trunk movement occurred (Sprigle et al., 2003). In their study they used 3 different cushions:

  1. Jay 2: viscoelastic fluid and polyurethane foam encased in vinyl atop non deforming foam
  2. ROHO High Profile: single-valve adjustable air
  3. Varilite Evolution: bonded multistiffness polyurethane foam encased in single-valve adjustable air cushion.

 

And found that the posture adopted by wheelchair users is a more important influence on upper extremity than is the cushion (Sprigle et al., 2003). None of these cushions is pre-contoured or consists of compartmented air. Therefor none of these cushions can create the stable base Sprigle refers to.

 

In 2018, Vreede et al. performed a case-control study where both healthy controls and individuals with a disability who relied on a wheelchair for daily ambulation performed a modified functional reach test, also known as the seated functional reach test (SRT), while sitting on different wheelchair cushions (foam + gel contoured cushion, interconnected air cell cushion, and two compartmented air cell cushions; the Vicair Vector O2 and the Vicair Adjuster O2) and a foam cushion which was considered the gold standard. In healthy controls, upward and horizontal reach are highest in both compartmented air cell cushions. Downward reach is highest in one of the compartmented air cell cushions. In disabled individuals, upward, horizontal and downward reach are highest in both compartmented air cell cushions, because they provide the most stable sitting surface . For both groups, there is a statistically significant difference in reach between the gold standard and the compartmented air cell cushions. Indicating an increase of postural stability when using a compartmented air cell cushion (Vreede, 2018).

 

In 2013, Nag et al., assessed COP on different seat cushions (cotton, foam and wooden) in 9 healthy participants. When participants sat on the foam cushion (polyurethane foam, covered with rexine), they showed significantly lower COP trajectory length and speed than when sitting on the cotton cushion or the wooden cushion, indicating that they experienced more postural stability on the foam cushion (Nag et al., 2013).

The study of Delazio compared multiple cushions, but only the results of an interconnected air cell cushion with and without closed valve in comparison with a foam cushion are shown. They found that airflow restriction in air cell cushions has a beneficial effect on stability due to a lower tilt response and better pressure distribution (Delazio et al., 2019). Since a Vicair cushion consists of SmartCells, al containing the air, according to the theory of Delazio they should be more stable compared to interconnected air-cell cushions. The comparison with and without a postural insert beneath cushion indicated that postural insert increased stability (Delazio et al., 2019).

 

  1. Discussion

The aims of this review were to determine what factors influence postural stability in a sitting position, what determining factors in a wheelchair cushion are to obtain optimal postural stability, and how this data is relevant for Vicair wheelchair cushions.

 

The 4 most important factors determining postural stability that were found in our literature search, were trunk strength, increase of base of support (i.e. using rigid footrests), anterior pelvic tilt and thigh support (Amos et al., 2001; Chari & Kirby, 1986; Hastings et al., 2003; Ilha et al., 2020; Y.

  1. Janssen-Potten et al., 2002). Two of these factors, anterior pelvic tilt and thigh support, can be obtained by selecting the right wheelchair cushion. Two studies found that cushion material greatly contributes to the amount of postural stability that can be obtained (Aissaoui et al., 2001; Vreede, 2018).

 

While Aissaoui et al. reported that postural stability increased most on a contoured foam cushion, Vreede et al. found that an even larger amount of postural stability could be achieved when a compartmented air cell cushion was used, a type of cushion which Aissaoui did not test (Aissaoui et al., 2001; Vreede, 2018).

The compartmented air cell cushions provided better postural stability than the interconnected air cell cushion and contoured foam cushion that were tested in all three studies, which not only allowed the user to reach further during the seated functional reach test, but allows users more independence in ADLs, social functioning and satisfaction with the equipment. All these factors are contributors to the quality of life experienced by the wheelchair user (Chen et al., 2003; Gao et al., 2015; Trefler et al., 2004).

 

The influence of back support on postural stability is only present during static seating (in a resting position) when contact between the back support and pelvis is present. However, during reach or dynamic sitting this contact is lost resulting in a negligible effect of the back support. The effect of the wheelchair set-up on stability is individually and task specific.

 

Although only one study focusing on wheelchair cushions included compartmented air cell cushions (Vicair Vector O2 and the Vicair Adjuster O2), the compartmented air cell cushions were compared to the same cushions (Jay 2, ROHO, Varilite) that were tested by Aissaoui et al. and Sprigle et al. (Aissaoui et al., 2001; Sprigle et al., 2003; Vreede, 2018). So the study of Vreede is not an isolated study and can be compared to the studies of Assaoui and Sprigle. The fact that Vreede found that compartmented air cell cushions are the most stable cushions is in line with what Delazio found, namely that airflow restriction in air cell cushions has a beneficial effect on stability due to a lower tilt response and better pressure distribution (Delazio et al., 2019). Since a Vicair cushion consists of Smartcells, al containing the air, according to the theory of Delazio they should be more stable compared to ROHO cushions.

 

5.  Conclusion

Postural stability is an important factor for independence and social functioning, which leads to increase of quality of life experienced by wheelchair users. Furthermore, the role of trunk control on shoulder injuries may be an important consideration in mitigating injury and improvement of wheelchair propulsion.

Therefore, selection of an adequate wheelchair cushion is of utmost importance to ensure a satisfactory quality of life of wheelchair users. Increase of postural stability in a sitting position can be obtained by using a compartmented air cell cushion.

 

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