DME

Blog posts of '2021' 'June'

To change or not to change.  When MWD (mid-wheel drive) chairs prove challenging


A frequent conversation I’ve had in recent weeks has been around drive wheel configuration and working out what drive wheel configuration may best meet a persons needs.    

In this part of the world we frequently prescribe mid-wheel drive (MWD) power wheelchairs, with their manoeuvrability working well in a variety of indoor spaces and improvements in suspension making them more user friendly outdoors, making it a chair that can meet an assortment of needs. But sometimes a MWD chair doesn’t work as well as we hoped and we are left trying to problem solve whether we can adjust the chair to make it work, or whether we look at whether another drive wheel configuration might work better.
 
Some of the common issues that get raised with MWD chairs include difficulty positioning a person’s feet, the person reporting the chair is difficult to use outdoors, or that using the chair outdoors impacts on their sitting tolerance.  Sometimes these issues can be improved by a change of set up, but other times it is the limitations of a MWD chair coming into play.
 
Let us start with looking at drive wheel configuration and castorsas the different base configurations have their benefits and challenges.  A front wheel drive (FWD) chair has the drive wheel at the front and two trailing castors, this arrangement lends itself to good outdoor performance as the front drive wheel can easily climb small obstacles.  Historically FWD chairs were prone to ‘fish tailing’ making the chair challenging to drive at faster speeds, however this has been overcome with improvement in drive tracking technology.  Some FWD chairs may have small anti-tip wheels on the front depending on their speed setting or power seat functions used on the chair.
 A MWD chair has its two drive wheels in the centre of the chair, with two castors sitting in front of the power wheelchair base and two castors at the rear providing stability to the base.  Advancements in MWD technology have resulted in improved suspension, a feature of this being castors that have some ability to rise and fall, helping overcome the historical issue of ‘high centering, or when the drive wheels become suspended when the chair traverses a steep road crossing.
 
Rear wheel drive (RWD) chairs have the large drive wheels towards the rear of the chair with two castors at the front, these chairs tend to be the easiest chairs to drive at higher speeds,but have a larger turning circle making them more challenging to use indoors.  Historically RWD chairs have been popular with users who frequently drive their chairs outdoors.
 
Remember also that where the drive wheel is positioned also impacts on how the chair moves. Many users will have a drive wheel configuration preference based on how the chair drives and how well this works in the environments they need to access.
   
Coming back to some of the commonly encountered MWD issues.  For wheelchair users who sit with their feet spaced apart, perhaps due to limitations in joint range of movement or oedema, how wide their feet can be positioned in a MWD (or RWD) chair is limited by the width between the two front castors.  For some users, the position of their feet is simply too wide for them to sit between the two castors, while others they may have issues with the front castors knocking their ankle when turning, or they have difficulty keeping their feet on the footplate – placing them at risk of injury if their foot gets caught between the footplate and the front castor.  For users who are hoist transferred and have good hamstring range, using 70 degree swing away hangers may overcome this problem, however for those who stand transfer in/out of their chair, changing to a FWD option may work best, however you may be limited by what power seat functions you use if you want to avoid the anti-tips wheels at the front.
The second issue that is often reported is the user reporting that using the chair outdoors increases their pain, or their tone increases resulting in a loss of positioning.
 
Simple but sometimes effective ways to improve ride quality can be to look at a person’s seating (air or gel based seating may offer benefit over foam) or swapping solid tyres out for pneumatic, but sometimes it is the two extra castor wheels in contact with the ground that is causing the issue.  When a chair encounters a small obstacle, how the chair responds depends on its drive wheel configuration.  Thinking about something like a low threshold to enter a home, for a RWD or FWD chair, only two sets of wheels need to manage the thresholdwith the first set of wheels heading up and over then the second set following, much like how a standard vehicle would manage such a threshold.  For a MWD chair managing that same threshold, the front castors would rise up and over the threshold, then the drive wheel (which is positioned under the user) and then the rear castors, this has a very different feel for the user, and for some users this subtle difference can be enough to cause issues.  When looking at base options for ride quality, don’t forget about your suspension options – not all suspension is created equal, and suspension options vary between model of chair. 
 

A third and less common issue that can arise with a MWD chair relates to where a user’s weight is distributed on a chair and how the chair performs, particularly outdoors.  On a MWD chair the user’s weight ideally needs to be distributed over the power wheelchair base  with their pelvis positioned either above or slightly behind the drive wheel. 

For children and people of short stature, it may not be possible to position them over the drive wheel as their thigh length is too short, meaning they sit towards the front of the chair.  For this group of people, a MWD chair may feel more like a RWD chair to drive, as the drive wheel is positioned behind them, or it may be that the chair struggles to get traction on softer surfaces such as grass or gravel as the person’s bodyweight is towards the front of the chair, not down through the drive wheel.  Changing to a front wheel drive can help overcome these issues and can also result in a base that has a shorter footprint which can be more in keeping with the person’s size.

For adults, their bodyweight may be focused towards the front of the chair for a couple of different reasons.  If a person has shortened hamstrings, they may be positioned towards the front of the seat pan to keep their feet away from the power wheelchair base itself, meaning their pelvis is sitting in front of the drive wheel.  Or it may be that the person has significant lower limb oedema and carrying extra fluid in their legs, or has extra body weight that is carried in front of them, so while their pelvis may be in line with the drive wheel, their body weight is distributed towards the front of base.  In these situations, having extra bodyweight towards the front of the chair can mean the suspension on the front castors is already loaded by the person’s bodyweight, hence when the chair is used outdoors, the castors have a limited ability to move and hence road crossings can become more challenging.  For some chairs they may also be more sluggish to turn on carpet, as more force is required to turn the castors which are carrying more load than intended.  Changing to a FWD chair typically overcomes these issuesas the drive wheel is now positioned where the castors previously were, with the drive wheel being more suited to carry this load.  As a side note, positioning a person towards the front of the seat pan can also influence how the power tilt actuator functions on some chair models, with the actuator prone to early failure if the setup is not ideal.  

Not sure if one of these situations is relevant to a person you are prescribing a chair for?  

Reach out to your local technician/dealer/supplier and seek a second opinion, with a front and side on photo of the person in the chair to share if possible.  Getting the drive wheel configuration right for a person can make a big difference in how well a power wheelchair functions for a person, maximising their mobility and what they are able to achieve. 


  

Rachel Maher
Clinical Education Specialist

Rachel Maher graduated from the University of Otago in 2003 with a Bachelor of Physiotherapy, and a Post Graduate Diploma in Physiotherapy (Neurorehabilitation) in 2010.
 
Rachel gained experience in inpatient rehabilitation and community Physiotherapy, before moving into a Child Development Service.Rachel moved into a Wheelchair and Seating Outreach Advisor role at Enable New Zealand in 2014, complementing her clinical knowledge with experience in NZ Ministry of Health funding processes.
 
Rachel joined Permobil in June 2020, and is passionate about education and working collaboratively to achieve the best result for our end users. 
 

How to set up a ROHO® QUADTRO SELECT® Cushion

 

The ROHO® QUADTRO SELECT® Cushion is one of our most popular choice of cushion. For those of you who are less familiar with the functionality, how to correctly set-up or adjust this cushion, or perhaps, why you would choose this style of cushion from our ROHO® range, then this week’s blog post is for you.

What is a QUADTRO SELECT® Cushion? 

It is an adjustable, air-filled, cellular-design wheelchair support surface that uses our DRY FLOATATION ® Technology.  The cushion is intended to conform to an individual’s seated shape to provide skin/soft tissue protection, positioning and an environment to facilitate wound healing.  

Although there is no weight limit, the cushion must be properly sized to suit the individual. 

The QUADTRO SELECT® cushion features four independent compartments of air cells, each controlled by our exclusive ISOFLO® Memory Control located at the front of all Select Series cushions, this includes our CONTOUR SELECT® Cushion

What is the ISOFLO® Memory Control? 

The ISOFLO® Memory Control allows air to flow through the cushion in two ways:

ISOFLO Memory Control shown in the OPEN position.

Air can flow freely throughout the entire cushion, similar to a ROHO® Single Compartment Cushion.

ISOFLO Memory Control shown in the CLOSED position.

Air becomes locked into four separate quadrants, offering front-to-back and side-to-side positioning capabilities. 

The cushion is available in our 3 profiles. High Profile which has a 4 inch cell height, Mid Profile which is a 3 inch cell height and our Low Profile which is 2 inch cell height. The set up is the same with all 3 profiles.

 

Why does the ISOFLO® Memory Control look different?

There has been a minimal design change to the ISOFLO ® Memory Control. The function remains the same however the lock and unlock icons have been replaced by a green circle, indicating a single compartment cushion, or 4 red circles indicating a 4 compartment cushion.

Before Re-Design

After Re-Design

 

Who would benefit from a ROHO® QUADTRO SELECT® Cushion?

The Quadtro or Contour Select is a great choice if an individual needs a cushion that provides both pressure redistribution and positioning needs. Consider the individual who is sitting in a posterior pelvic tilt and the impact this posture has on the persons ability to eat, drink, talk and breathe! The goal is to ensure the individual is sitting in the most comfortable and midline posture as tolerated.

The set up guide below will explain how to set up the select cushion range, as a single or four compartment cushion and how to either accommodate or correct a posterior pelvic tilt or pelvic obliquity using the ISOFLO® Memory Control.

How to set up a ROHO® QUADTRO SELECT® Cushion

We have created a simple QUADTRO SELECT® Set Up Guide which you can access here.

For those of you who are more of a visual learner, here is a great animated video showing the correct set up of a QUADTRO SELECT® Cushion. 

 

 

 

 
Dee Smith 
LTC / Aged Care Clinical Specialist  

Dee is a Registered Nurse with almost 25 years’ experience in a variety of specialities.   

She graduated from Sydney University with a Bachelor of Nursing in 1997 and in 2001 gained a Post Graduate Certificate in Infection Control. She has Certificate IV in Training and Assessment.  

Over the past few years Dee has been working within the Aged Care Industry as a Clinical Nurse Consultant in Infection Prevention & Control, to assist Residential AgeCare Facilities in meeting the requirements for the Aged Care Quality StandardsDee developed and delivered education and training of evidenced-based practice in Infection Prevention and Control, Wound Care and Pressure Injury Management.  

Dee joined Permobil in 2020 as the Seating and Positioning BDM and in 2021, joined the Asia Pacific Clinical Education team as Long Term Care/Aged Care Clinical Specialist. Dee is passionate about mentoring, educating and empowering health care professionals to provide safe and quality care.