Welcome to Part 2 of this series exploring the effect back supports can have on sitting posture. First, to recap:

The back support height and width selection is dependent on a number of factors. The base of the back support generally runs from the height of the posterior superior iliac spines (PSIS) to the chosen height against the user’s back depending on the support needed for stability and the freedom of movement required at the shoulders (e.g. if a wheelchair user is self-propelling).

The cushion and back supports are primary surfaces involved in functional seating and both have a direct effect on sitting posture. This is a two-part blog that explores how the back support can offer biomechanical support to maintain pelvic alignment and stability, particularly in the transverse plane (pelvic rotation) and sagittal planes (posterior/anterior pelvic tilt).

We reviewed how the back support can respond to pelvic rotation in Part 1, now let’s explore the following question:

How does the back support offer postural support to the pelvis in the presence of anterior and posterior pelvic tilt?
Neutral Alignment
Anterior Pelvic Tilt
Posterior Pelvic Tilt
How can the back support be contoured to respond to pelvic tilt?
Non-reducible anterior pelvic tilt
Reducible anterior pelvic tilt
Non-reducible posterior pelvic tilt
4. Reducible posterior pelvic tilt
Closing thoughts

A pelvis that is level from the ASIS to PSIS on the wheelchair cushion helps to maintain the natural curves of the spine in the lumbar, thoracic and cervical regions. When we sit, we tend to move into slight posterior pelvic tilt. For this reason we tend to find our most commonly used seat systems (e.g. car seat, office chairs, some armchairs) include an optional lumbar support to maintain a neutral pelvic tilt and optimal trunk alignment whilst we are seated on them.  We need to first consider our seat cushion and then our back support cushion, in order to optimise our sitting position in a wheelchair.

The back support angle might also be slightly reclined to meet the pelvic alignment and help the trunk rest against the back support – this position can support a relatively neutral pelvic tilt, but is likely to require contouring in the lumbar regions.

We all adopt different sitting postures depending on our seating surface and, because our body shapes are unique and comfort on the same seating system can vary, we need to consider a combination of contouring and angle adjustment in the seat and back support in the same way as we will not all find the same office chair comfortable in a single configuration.

Back supports should optimise pressure distribution and stability to the pelvis and trunk. The back support can have a direct effect on sitting posture and our aim is to optimise the contouring to positively influence posture to reduce pain during prolonged sitting periods and encourage optimal alignment to support function for quality of life.

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