Our bodies are designed to move. We move to reach a destination, complete a task, alleviate discomfort, and provide sensory input. Yet many people using manual and power wheelchairs are unable to move their body within a static seating system. If the client is able to move, the support surfaces do not move with their body, resulting in shear and loss of posture. Unrelieved forces can also lead to client injury as well as equipment damage.

What is Dynamic Seating?

Dynamic Seating provides movement within the wheelchair seating system and/or frame. The Rehabilitation Engineering and Assistive Technology Society of North America (RESNA) Position Paper on the Application of Dynamic Seating defines this intervention as:

“Movement which occurs within the seating system and/or wheelchair frame in response to intentional or unintentional force generated by the client. Dynamic components absorb force. When client force ceases, the stored energy is returned through the dynamic component, which in turn assists the client back to a starting position (Lange, et al., 2020).”

A key part of this definition is that dynamic seating moves in response to client force. Power seating, such as recline and elevating legrests, provide movement of the client – however, this movement must be triggered somehow (by a toggle or switch) and does not automatically respond to client forces and return when those forces abate.

Some wheelchairs incorporate dynamic seating. Other dynamic seating options are modular and can be added to a new frame or retrofitted to an existing frame. These modular components can be used in isolation or in combination. Dynamic components primarily provide movement at the hips , knees and ankles, and neck.

Who is Dynamic Seating appropriate for?

It can certainly be argued that everyone needs to move. With that said, dynamic seating is used in three primary clinical scenarios.

Scenario 1

Dynamic seating can be used to absorb extensor forces that could otherwise lead to client injury, loss of equipment alignment or breakage, decreased sitting tolerance, increased agitation, decreased function, further increases in extension, and energy consumption.

Let’s take a look at Daniel. Daniel is now in his early 20’s and has cerebral palsy, seizures, and cerebral visual impairment (CVI). He is non-verbal and non-ambulatory. He uses a communication device.

When Daniel was 10 years old and still in a static wheelchair, he exhibited significant extensor tone throughout his body that ultimately led to a hairline fracture of his right femur. He also dislocated both patellae and his knees were red and swollen. Finally, he dislocated both elbows. His medical team had placed a Baclofen pump, however this led to complications and had to be removed. In addition to these injuries, Daniel had damaged the seating system, mounting hardware, and wheelchair frame over the years.

Daniel has been using dynamic seating interventions for a number of years now. He started with an integrated system that incorporated a dynamic back and dynamic footrests. When this was outgrown and discontinued, he switched to a manual tilt in space wheelchair with modular dynamic back, dynamic footrests, and dynamic head support hardware.

Since using dynamic seating, Daniel has not experienced any further injuries and his knees are no longer red and swollen (see figure 1). He has not damaged any equipment since. He can tolerate sitting in his wheelchair for much longer periods of time and his active extension is reduced, conserving his energy for other tasks.

To watch a video of Daniel using his Dynamic Seating, click here 

Scenario 2

Dynamic seating can be used to provide movement and sensory input (vestibular and proprioceptive), increase alertness, and decrease agitation.

Let’s take a look at Phillip. Phillip is an adult with developmental disabilities who has increased muscle tone throughout his body. He is non-verbal and non-ambulatory. He seeks out movement and tends to rock his entire body in his manual wheelchair for much of the day. As this wheelchair does not include dynamic components, this rocking has led to repeated damage of the base. Specifically, he has broken back canes and damaged the tires. His team locks the wheels to keep him from rolling across the room as he rocks. His rocking is so strong, that sections of the tires actually break off under the wheel lock. He often extends his knees while rocking. Finally, Phillip tends to bang his head with force against the head support – this has even led to a bald spot on the back of his head.

A new manual wheelchair was recommended with a dynamic back, dynamic footrests, and dynamic head support hardware. Phillip has been using this for 5 years now and has not broken anything on the frame. He can readily rock, which increases his alertness and decreases his agitation. The hair on the back of his head even grew back!

To watch a video of Phillip before and after Dynamic Seating, click here

Scenario 3

Dynamic seating can improve postural control and stability, as well as function. How? By providing movement within a small range against light resistance, muscle strength increases which, in turn, improves postural control – particularly trunk and head control. Increases in muscle strength and postural control can also improve overall stability which can have a positive effect on function.

Let’s take a look at Oliver. Oliver is a young boy with seizures, spastic quadriplegia, and CVI. He has received extensive therapies to maximize his overall development. He had low tone in his trunk and emerging increased tone in his extremities. Oliver used an adaptive seat with a dynamic back . As he moved against this light resistance, his physiotherapist noted that his core was strengthening, resulting in improved trunk and head control. She and Oliver’s family also noted that his constipation improved with the addition of this movement. Oliver eventually received a manual wheelchair with a dynamic back, as well.

To watch a video of Oliver in his Adaptive Seating System with Dynamic Back, click here

Other Clinical Benefits

Research supports the above clinical benefits and more. The RESNA Position Paper includes an extensive literature review. An additional literature review, which is regularly updated, is available here.  

Design considerations

A great deal of design goes into dynamic seating. This design must allow movement of a body part, return the client to a starting position without loss of posture, and be durable enough to move under force and not break.

Dynamic Backs are designed to place the pivot point as close as possible to the natural pivot point of the client’s hip. If the pivot point is too low, the client may slide into a posterior pelvic tilt upon return to a starting position. Ideally, the pivot point should be at about the top of the cushion or seating surface. The amount of movement is also key. If the back extends too far, the client is more likely to experience shear forces and loss of alignment with the back support surface. A smaller degree of movement, such as 15 degrees, still diffuses force, but with minimal shear and loss of alignment. This degree of movement allows the use of a dynamic back even with a moulded seating system. Most dynamic backs are also designed to ‘lock’ or ‘latch’ during transport.

Dynamic Footrests are perhaps the most complex of dynamic seating components. A dynamic footrest may telescope downward, extend at the knee, and flex / extend at the ankle. Combining telescoping, extension, and ankle plantar flexion follows the natural arc of the leg during extension. If a client has very tight hamstrings, they may benefit from using only the telescoping feature to absorb and diffuse force and provide some movement. A client with very limited hamstring range may end up in a posterior pelvic tilt if knee elevation is used. If a client is wearing Ankle Foot Orthoses (AFOs), dynamic movement at the ankles is not necessary. The pivot point for knee extension should be as close as possible to the natural pivot point of the knee. Otherwise, the client’s forces may not activate the dynamic component at all, or not efficiently. Angles are important.

Dynamic Head Support Hardware can be used with compatible head pads. This hardware is designed to move in response to neck extension and/or rotation, but not allow the client to assume a position of neck hyperextension. Some of this hardware is only designed to respond to posterior movement and will not activate if the client also rotates. The dynamic component itself (i.e. springs) must be shrouded in some way to prevent the client’s hair from being pulled.

Resistance is also a key in dynamic seating design. Dynamic seating may use hydraulics, springs, or elastomers to absorb and store energy. Some dynamic seating options only come with one level of resistance when ordered – meaning that the evaluation team must select the optimal level of resistance at order, often without the client trialing it first. Other dynamic seating options are shipped with the full spectrum of resistance options so that this can be readily changed to meet the individual client’s needs at or after delivery.

So how do we choose the optimal resistance level? In general, if the resistance is too high, the client will be unable to activate the dynamic component. If the resistance is too low, the client may activate the dynamic component, but not readily return to a starting position. The dynamic component (i.e. elastomer) may need to be replaced periodically for wear and tear.

Conclusion

While everyone needs to move, dynamic seating is not always indicated. Most dynamic backs do not fold down for transport. Dynamic seating is not compatible with every available manual and power wheelchair. This technology adds weight to the wheelchair frame. But for clients like Daniel, Phillip, and Oliver, dynamic seating has a multitude of strong clinical benefits. The wheelchair seating and mobility team must keep this option in mind, when appropriate, to better address client needs.

References:

Lange M, Crane B, Diamond F, et al. RESNA position on the application of dynamic seating. Washington (DC): Rehabilitation Engineering & Assistive Technology Society of North America; 2020.

About the author 

Michelle Lange (photo above) is an occupational therapist with 35 years of experience and has been in private practice, Access to Independence, for over 15 years. She lectures both nationally and internationally, and has authored numerous texts, chapters, and articles. She is the co-editor of Seating and Wheeled Mobility: a clinical resource guide, editor of Fundamentals in Assistive Technology, 4^th ed., NRRTS Continuing Education Curriculum Coordinator, and Clinical Editor of NRRTS Directions magazine. Michelle is a RESNA Fellow and member of the Clinician Task Force. She is a certified ATP, certified SMS, and is a Senior Disability Analyst of the ABDA.