Let’s get it clear: What makes a good cushion? 3 – Stability and a neutral pelvis

Let’s get it clear: What makes a good cushion? 3 – Stability and a neutral pelvis

This short article examines the first elements around the subject of posture and positioning, considering the role of stability, the health benefits of a neutral hips, and how this can be accomplished.

This is the third post in a series which aims to assist people to believe more about what it is that enters into a cushion that makes it great for one individual, however possibly not for another.

In the very first post, we recognized the three key components around which a cushion can be assessed– functionality, posture management, and tissue integrity.

By Dr Barend ter Haar

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Figure 1. Metastable and steady match boxes

. In this post, and in Part 4 of the series, we check out components which can be designed into a cushion in order to assist keep the hips in a central or neutral position, to counteract the effects of gravity attempting to pull the individual away from this metastable position, and to allow optimum performance.

We stress the value of stability, but what do we mean? Stability is a fascinating term when it is applied to the seated individual, and around what that individual can do. If we take a matchbox, and location it on its end, it might be considered to be stable. It might be knocked over to a more stable position on its side (Fig 1). The former is understood as being metastable when one has a so-called steady item that can be transferred to a more stable position.

For the clinician, along with for the occupant, tissue integrity of the seated location may probably come initially when choosing the qualities of a cushion. The building and construction and stability of the aspects of the cushions design will have major results on the occupants ability to bring out their typical activities while seated on their cushion. In addition, without suitable support and stability at the hips, there are possible knock-on effects to the occupants health, e.g. from misalignment of the spinal column leading to pain and to associated effect on the physiological processes within the torso.

Neutral pelvis


What do we mean by a neutral hips? A neutral hips is where the Posterior Superior Iliac Spines (PSIS) (Fig 2: K) and Anterior Superior Iliac Spines (ASIS) (Fig 2: L) are level with each other in the horizontal aircraft (approximated visually by the line of your belt): this equates to the hip joint (Fig 2: M) and the iliac crest (Fig 2: J) being aligned vertically.

For a seated person, metastability is possibly more practical than full stability in that it permits the individual to move their centre of gravity more towards the edge of their seating location– however, this only works for the individual if the person has the ability to combat against gravity to return into the initial metastable position. So, in seating, the degree to which the cushion both helps the resident and supports as they reach sideways or forwards is crucial– a location now catered for and quantifiable in the brand-new ISO 16840-13 draft basic ¹

Figure 2: Alignment of the hips in a neutral position ²

Staying in this position can be strenuous, and the majority of individuals relax back into a pelvic posterior tilt where the PSISs become lower than the ASISs. In setting up the seat, it is not unusual to permit a couple of degrees of posterior tilt for convenience.

Playing ball with the pelvis.

So what can we do within the seating and cushion style to fight this posterior tendency? The hips acts a bit like a basketball, in that it can turn in three airplanes, and with posterior tilt, it rotates in the anterior-posterior aircraft.

. Subsequently, the spine will be at its straightest at this moment, and the torso and head at an optimum height. This extended shape of the spinal column provides the most advantage to the upper body, allowing maximum breathing, digestive, cardiovascular, and bladder function, and allows the head to be positioned finest for communication and other functions.

Therefore, the first thing we need to do is put the hips on a horizontal aircraft if we desire the hips to be neutral. Many wheelchairs are provided with a dump with the seat plate angled upwards (which is frequently employed to make the occupant feel more steady and protected, on the one hand, and to bring the knees higher and the feet off the ground, on the other). This disposing does not provide a horizontal base and ideas the hips back into a posterior tilt.

Fig 3 Protecting versus posterior tilt ³

Next, to stop the pelvis from slipping forward, a little ridge anterior to the ischial tuberosities can be very efficient (Fig 3: 2). Try folding a tea towel 3 times and location across your dining room chair, midway back from the front edge, and see just how much distinction that makes in managing your ability to move your behind forward on the chair.

Pre-Ischial ridge.

. The solution is to have the seat plate horizontal, and therefore the pelvis neutral, but put a wedge under the cushion at the anterior part of the plate, consequently both raising the knees and allowing pressure redistribution away from under the hips to listed below the thighs– to tissues more suited to bring the pressures (Fig 3: 3).

Figure 4: The benefits of a wedge under the ideas for pressure redistribution., FSA pressure map without wedge (left) and FSA pressure map with wedge (right).

If put inside the cushion cover, this wedge is finest. Using a pressure mapping system is the perfect methods to visualise where pressures are being most uniformly rearranged away from the hips and under the thighs. (Fig. 4).

We now have the pelvic ball on a flat surface area. How do we keep it from rolling backwards or forwards? The answer is, first, to position a PSIS block behind the hips, to stop the hips from rolling backwards (Fig 3: 4). This can be achieved by the base of a solid back support or with stress adjustable straps in a flexible back support.

Figure 5: Positioning of a pelvic postural support anterior to the greater trochanter ³


Click to read more from the Lets get it clear series from Dr Barend ter Haar.

Dr Barend ter Haar has been associated with seating and movement for over 30 years, including lecturing worldwide and establishing global seating standards.


In this post, and in Part 4 of the series, we explore components which can be developed into a cushion in order to assist keep the hips in a main or neutral position, to counteract the effects of gravity trying to pull the specific away from this metastable position, and to permit maximal performance.

There are lots of components that need to be taken into account when choosing what might be the most suitable cushion for a private, and these go well beyond the immediate medical requirements of tissue integrity and the occupants needs for performance. This article supplies a number of relevant services around positioning the pelvis and stabilising, under the posture and placing heading.

¹ ISO DIS 16840-13:2020 Wheelchair seating– Part 13: Determination of the lateral stability home of a seat cushion ² From Figure 25 of ISO 16840-1:2006 Wheelchair seating– Part 1: Vocabulary, referral axis convention and measures for body segments, posture and postural assistance surface areas ³ BS 8625:2019 Selection, placement and fixation of versatile postural support gadgets in seating– Specification (NOTE: Advice on the use and application of this standard is readily available from BES Healthcare Ltd.).

Further items can be discovered at www.beshealthcare.net. Please contact barend@beshealthcare.net if you are interested in receiving additional info on the subject.

. A comparable effect can be gotten by creating a buttocks recess in the cushion– the buttocks recess can likewise develop greater immersion into the cushion, and therefore better pressure redistribution (Fig 3: 1). The important component is that this depth must not be more than an optimum of 1cm, otherwise you risk increasing pressures on the anterior side of the ischial tuberosities and also you hinder the users metastability i.e. their opportunities to alter position in a self-controlled manner.

At this point, if not adequate control is being achieved, then a 3rd point of control– a positioning belt– need to be used. Keep in mind: this need to be mounted to the chair anterior to where the higher trochanter of the thigh bone is located (Fig 5) as described in BS 8625 ³


In addition, without suitable assistance and stability at the pelvis, there are prospective knock-on impacts to the residents health, e.g. from misalignment of the spinal column leading to pain and to associated effects on the physiological processes within the upper body.

The first thing we require to do is position the pelvis on a horizontal airplane if we want the pelvis to be neutral. Using a pressure mapping system is the ideal ways to visualise where pressures are being most uniformly redistributed away from the hips and under the thighs. The answer is, initially, to place a PSIS block behind the hips, to stop the pelvis from rolling in reverse (Fig 3: 4).

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