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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