Posterior Pelvic Tilt

Posterior Pelvic Tilt    

Last weeks live webinar looked at the very common posture that comes from a posteriorly tilted pelvis. Whilst we often discuss the pelvis as the foundation, it is important to appreciate that to support the pelvis back to a neutral position, the primary point of control comes from the backrest. Yes the cushion features will certainly assist as will a pelvic support belt, however we can’t overlook the crucial role the backrest plays. Today’s blog will take a closer look at pelvic blocks as a point of control for reducible posterior pelvic tilt (PPT)  

Pelvic Block

A pelvic block refers to the provision of an insert or contouring in the back support to adjust the force at the pelvis.  Providing an increased force at the posterior aspect of the pelvis can assist in both reducing a PPT and maintaining a neutral pelvis.

There are various ways we can create this force, lets take a closer look at some of the potential options. 


Tension Adjustable Backrests



If clinical reasoning identifies an upholstery back rest, I will always consider a tension adjustable option first. A tension adjustable backrest uses horizontal straps under the front upholstery. By adjusting these straps you can increase or decrease the force as required. Next time you have an opportunity I recommend you try it out. First sit in the wheelchair without adjusting it so you can feel the difference. Next loosen off ALL the straps. Now tighten the lower straps of the backrest from the seat base to the Posterior Superior Iliac Spine (PSIS)as much as you can. Now gently work your way up the straps doing each one above the tightened straps to follow the contours of the trunk position wanted. By having the lower straps tightened you will feel a more upright trunk posture coming from the increased force at the pelvis.



Another Back rest that uses a similar concept to a tension adjustability, is the Acta Relief. This is a unique backrest. Equipped with an oversized aluminum shell cut-out to allow deeper immersion into the back. It has adjustable Boa system that can be tightened and loosed off at different areas. Whilst a similar concept to tension adjustable straps, the Acta back can provide stronger points of control that maintain and do not slip as webbing straps can, but it has to be removed if chair is regularly folded.

Aftermarket Off The Shelf Back Supports

Most after market or ridged backrests consist of a shell and foam interface. Mounting brackets may provide adjustment for active seat depth and STB angle. You need to understand what you are trying to achieve before identifying appropriate equipment. There may be a standard adjustment such as a dual or hinged shell which enables the shell to be opened at a hinge joint usually just above the PSIS.

Some aftermarket back rests are supplied with dense foam wedges that can be placed between the shell and the foam interface, image 6  shows inserts provided with the  Dreamline contour back rest.


Adjustable Backrests

There are several adjustable backrests on the market that allow you to adjust the contouring of the support surface to create individualised support. These tend to work well with significant complex and asymmetrical postures, and for those with ongoing changing postural needs such as those with aggressive progressive conditions. I am frequently surprised when I see clients with these types of backrest with NO adjustment to the contour…it is as flat as the day it was packed at the manufacturers. Whilst we could consider these types of backrests for ongoing needs, they still need to be appropriately selected and individualised to the users current needs. I have had significant success in even minor adjustments through the trunk contour when the point of control has been set up appropriately and is proving the support required. Materials of the backrest are crucial when working with these adjustable backrests. Think critically with the clinical reasoning process, how much force do you want compared to how much immersion. What are you trying to achieve? With  a back support, it is essential to simulate the map findings and identify the impact of gravity and how you can achieve the required support for the end user. An adjustable back is easy to create a pelvic block in as you can adjust the contours to meet the users needs by taking out or adding in foam pieces. When you apply good contouring that provides the appropriate level of support you can create an appropriate solution for the user. 


These BAC pads made of a dense closed cell foam and are designed to be moved and overlapped so you can easily build up a pelvic block and other contouring as it is required. Pictured are the standard BAC. 

Making a Pelvic Block  

Not sure if a pelvic block would make a difference with a clients existing seating? Consider doing the towel trial.  Taking a small washcloth or hand towel fold it into several layers and place it at the pelvis area where you want support (seat surface to PSIS height), what I like about this method which I first saw over 15 years ago when Bengt Engstrom facilitated a workshop, was the ease in which to get further information. Most households will have a small towel to fold up and use. I could change the thickness and height to see the impact it could have just as I could place it in front of or behind the foam interface depending on the materials of the backrest.  Bengt is a Swedish Physiotherapist, author and original designer of our Corpus Seating System in the Permobil power bases.  I will use the towel as part of the assessment process, however it can be trialled if wanting to trial different thicknesses etc. I have made multiple pelvic blocks. I find an electric bread knife is a cost effective tool for these kinds of projects so keep one in my tool kit for these purposes.

Step 1 – Take a piece of foam in required density, it should be the thickness you are wanting, I often use a dense 1 or 2 inch.


Step 2 - cut a rectangle, approximately as wide as inner back rest (A)and height of seated surface to PSIS (B)

Step 3 - Chamfer off the top corner edge to create transition from pelvis to back support with knife

Step 4 - Attach between the shell and foam interface 


A individualised custom pelvic block to provide the force for a reducible posterior tilt… don’t forget the cushion and supports to complete the solution! If you have questions about any of the concepts or products featured please contact us at




Tracee-lee Maginnity
Clinical Education Specialist

Tracee-lee Maginnity joined Permobil Australia in July 2019, as a clinical education specialist. She graduated Auckland University of Technology with a BHSc (Occupational Therapy) in 2003 and has since worked in various roles related to seating and mobility including assessing, prescribing and educating.

Tracee-lee is passionate about maximising functional outcomes with end users and the importance of education within the industry.


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