Seat Slope’s Sweet Spot
Optimal Front & Rear Seat-to-Floor Heights Can Accomplish Amazing Things. The Challenge: Finding Them
- By Laurie Watanabe
- Aug 01, 2012
But for all the exactitude demanded of these professions, there is also the unique nature of each seating & mobility client: a clinical presentation, goals, environments, dreams and personal preferences that differ from every other wheelchair user. And that’s where seating & mobility becomes a more subtle and perhaps intuitive process — being able to craft a unique solution that, if done correctly, exactly fits only one person in the entire world.
One of the key factors that make up that unique solution is seat slope. It’s a simple distance expressed as a number: 2", maybe, or 3". Dialing in the right amount of seat slope can benefit a wheelchair user in many ways. But finding that ideal number for each client is the challenge.
When Slope Is Called For
“Seat slope absolutely can affect how the client sits in his/her wheelchair,” says Sharon Pratt, PT. “Most typically in the world of wheelchair seating, we think about seat slope as one that is lower at the back than the front, or lower at the front than back when we measure seat-to-floor height at the front of the chair and at the back of the chair’s sitting surface. This will affect posture as well as stability, and consequently, function.”
Having the front of the chair lower or higher than the back of the chair creates different angle measurements between the wheelchair seat and back.
“Let’s first think about a seat slope that is lower at the rear than the front when we measure seat-to-floor height,” Pratt says. “If the back support surface remains upright and unchanged, the lower the rear seat-to-floor height is in relation to the front seat-to-floor height, the more closed — squeezed — the seat-to-back angle will be.”
And that angle can be useful to the seating & mobility team.
“Seat slope or seat inclination is used for various reasons,” says Steve Boucher, OT, clinical educator for Sunrise Medical. “When we look at positioning, seat inclination is sometimes used to prevent a client from sliding forward in their chair.”
Boucher adds that seat slope can give self-propelling chair users better accessibility to their rear wheels, “especially those users who are very tall through their upper body. It allows a user to sit ‘in’ their chair rather than ‘on top’ of their chair. This afects the end user’s center of gravity and can make for better propulsion technique, which leads to someone not fatiguing as quickly in their chair.”
The positioning that seat slope off ers can help compensate for a wheelchair user’s loss of function, says Tricia Garven, PT, ATP, clinical applications manager for Th e ROHO Group.
“Very simply,” she says, “the lower you sink somebody’s butt — basically the greater that difference (in height) is from the front to the back — the more it makes up for in terms of lack of physical ability. You have more stability and you have more balance the lower you sink them. The lower we sink your butt, the more it makes up for in terms of what you lack in ability in your trunk and your core.”
Therefore, Garven says, high-functioning patients with quadriplegia — such as those with spinal cord injuries in the C6, C7 and C8 range — will generally sit “lower” in their chairs, i.e., with more seat slope, than consumers with paraplegia.
As with any positioning possibility, however, what works well for one consumer may not work at all for another.
Says Pratt, “For someone who may have limited hip flexion — and for example, during the hands-on evaluation it has been determined that the client does not have 90° of hip flexion without posterior pelvic tilting — then this low rear seat-to-floor height without change of the back angle could be a very negative experience, potentially causing sliding, discomfort, obliquity, etc. Th e hands-on evaluation will dictate whether of not the client can tolerate changes in seat slope.”
Finding the Right Seat-to-Floor Heights
“Rear seat height usually is a factor of wheel access,” says Kevin Phillips, ATP/SMS, CRTS, Experea Health Care of Lake Forest (Calif.), about determining the rear seat-to-floor heights for ultralightweight chair users. “Front seat height can be set depending on where somebody wants it. Maybe they need length for their lower legs; maybe they want to sit higher because they like the slope for stability. Maybe it needs to be flat because if they’re foot propellers, they can get more foot on the ground — like if somebody’s had a stroke, that seat slope might need to be flat to keep that front foot down low enough on one side so they can pull the chair.”
While seat slope is a common topic of conversation for people with spinal cord injuries, Phillips says the seat slope factors to consider can be very diff erent for clients with other diagnoses.
“When somebody has a movement disorder or spasticity, then seat slope introduces a whole new range of issues,” he notes. “If they’ve got a lot of dump in the chair, they can’t use gravity like you and I do for our lower extremities to manage what we’re doing with our upper bodies.”
Phillips compares that scenario to sitting at a desk and leaning forward to write. In that situation, he says, “Lots of people have their knees lower than their hips. Th ey’re leaning forward and being in a really active position. You can’t do that if you have a lot of seat slope, because your knees are higher than your hips. You can’t use gravity. It’s very different for somebody who has movement problems instead of just having lack of muscle tone. Lots of kids with cerebral palsy, or stroke patients do better if their seat slopes are flatter. They can manage the rest of their body better.”
While a consumer’s height isn’t part of the clinical diagnosis, taller people may be able to use a greater seat slope to give them greater access to their environment. Phillips points out that a tall person whose rear seat-to-floor height is significantly shorter than his front seat-to-floor height could, for instance, “still stay in a compact (ultralightweight chair) frame, but keep his feet from digging a hole in the ground as he’s going along.”
Compromises to Consider
As is almost always the case with seating & mobility, of course, selecting a certain seat slope for a client results in a change in position that impacts many other measurements and functions. And with seat slope, those impacts are especially important to note because once it’s dialed in, seat slope is not easily changed compared to other wheelchair settings.
“In an ideal world,” Pratt says, “we would be able to change angles, shapes and orientation throughout the day because sitting, in my opinion, is a dynamic activity and a lot of work. However in the wheelchair seated world, seat slope is not oft en changed during the course of the day. Seat slope in wheelchair seating is usually set at the time of ordering and/or delivery.
“If it needs to be changed, it often can be dependent upon the wheelchair seating combination. But not usually by the client during the course of the day based upon varying activities.”
Boucher concurs, citing a lack of convenience: “Typically, an end user will not change their seat slope throughout the day. It can be very time consuming depending on their condition, and oftentimes there are multiple adjustments that must be made to various parts of the wheelchair aside from the rear axle. Squaring casters, moving a footplate up or down may also need to be completed. Th is level of adjustment can cause the chair to not roll properly if these adjustments are not made correctly. Those individuals who have been in a chair for a while may change seat inclination from time to time, but I would not say on a consistent basis.”
Among the bigger concerns caused by seat slope: whether the client will be able to transfer efficiently and safely from a chair that has a lower rear seat-to-floor height than a front seat-to-floor height. That particular configuration — in which the client literally sinks into the back part of the seat cushion and chair — typically makes it more difficult for the client to lift himself out.
Because that type of more significant seat slope is often used by consumers with quadriplegia, who like the increased stability that increased seat slope offers, and you can have the perfect storm when it comes to transfers: People who have less strength and control of their upper bodies are required to do more work to lift themselves up and out of the chair.
Phillips remembers a client in that situation.
“He had a C5-6 injury, and he doesn’t have a lot to work with,” Phillips says. “Th e way that he’s been able to transfer by himself for almost 30 years is having a real tall seat-to-floor height that’s flat, so he doesn’t have to work himself out of a hole. He’s a tall guy, so that tall seat-to-floor height means he’s pretty level with a lot of things he’s transferring in and out of. If he were in a lot of seat slope, he probably wouldn’t be able to get himself forward and balanced to make his transfers.”
But then again, facilitating transfers causes ripple effects, too.
“You have to consider that if somebody is going to be truly independent, you don’t want to take away their independence in transfers,” Garven says.
But if that person will require help in making transfers anyway, “then they may be better served sitting with greater seat slope that makes the transfer more difficult, because they’re not transferring many times per day, and maybe they could be independent for six or eight hours. It’s a trade-off you have to evaluate.”
For instance, Garven says, while increased seat slope may cause a client to require help with transfers, that slope may enable him to be more independent during much of the rest of his day. “He’s able to propel himself, and he has balance,” she says. “He is able to do bilateral tasks now — he can push, open the door, and go through it.”
Changes in the Seat Slope Equation
While seat slope itself is a matter of straightforward mathematics, other factors related to it have evolved, Phillips says.
For instance, in the past, “a lot of that stability had to come from seat slope because the seating surface wasn’t as stable,” he notes. “And so by squeezing the user more in between the angle of their seat base and the back, it gave them stability that they otherwise would have been lacking. Now, however, with so much custom orthotic seating, seat slope isn’t so necessary for stability as it used to be.”
There are also other ways to emulate the benefit of seat slope without actually changing the slope itself, Boucher says.
“What we do tend to see more is that rather than change seat inclination, an end user may make adjustments to the seat-to-back angle on their chair due to fatigue, propulsion, spasticity,” he says.
“You can do a lot with the cushions,” Garven says, “with the combination of cushion and backrest specifically to create a lot of stability with just a little bit of contour. You can create a lot of stability that way, too — the goal being whatever is functional for that person. The goal being: push all day, sit all day, comfort all day, of course no skin breakdown. Being as independent and functional as possible.”
And while seat slope is oft en talked about in conjunction with manual self-propelled chairs, the always-improving functionality of multiple powered positioning elements can also emulate seat slope’s accomplishments.
Phillips says, “I think ultralight wheelchairs are the most difficult pieces of equipment to configure. Th e ultimate function of a custom ultralight chair depends on everything being dialed in just right, and there are so many little details. What about the width of the seat and the length of the seat depth and the length of the frame and how big your casters are and how big the wheels are, and where the wheels are?”
Going back to the earlier example of a client with C5-6 spinal cord injury, he adds, “If I’ve got to order a power wheelchair with tilt and recline and power legs, it doesn’t really matter where a lot of (other elements) are set, because he can adjust the seat position with the controls in the power chair. But on the manual chair, everything has to be in just the right place.”
The Importance of the Evaluation
“Every user is different,” Boucher says when asked how seat slope function should be determined for a client. “What we typically tend to see is that new users start off with .5" to 1" of seat inclination. Often they are still adapting to their new body, and trying to figure out their position in space so increased seat inclination is not often used. As a client becomes more comfortable with their center of gravity, balance, and strength, adjustments are made.”
“In general, the adjustable chairs are ordered in the beginning because you can have somebody with a little bit flatter seat until they get better at transferring,” Garven says. “Then you can start to lower them down and down in the same chair, just different configurations. Once they find that sweet spot where they really want to be, you can order that chair locked into that position and save a bunch of weight because you don’t have all that adjustability.”
“It’s really a good thing to be able to nail the configuration rather than to have chairs with a lot of adjustability, because those chairs weigh typically several more pounds, and most people don’t end up adjusting their chairs anyway,” Phillips says. “Where I work now, we do a lot of custom manual wheelchairs, and they’re pretty much all fixed seat angles. It’s really rare that we sell a chair that has an adjustable seat slope. You can determine most of the time what that seat slope should be with a good evaluation.”
That evaluation, says Pratt, includes “where range of motion, stability and function are thoroughly investigated. From there, a trial of equipment would validate the desired setup prior to finalizing the order. Factors coming into play would be hip flexion, neuromuscular control and skin integrity, for example.”
While working with a seating & mobility clinician, Phillips says, “We always make sure the patient gets out of whatever he’s sitting in, and sits on a mat where he’s not supported by anything. Ask those questions: ‘How do you transfer, what do you transfer to, what do you like about the way that you’re sitting? If we changed your seat like this, went up or down, how is that going to affect all the things that you do?’ That’s where all the answers come from.”
And then, Garven adds, it’s imperative to truly hear what the client is saying.
“If they tell you, ‘Xyz solution won’t work, we tried it two years ago, it doesn’t work in my house, it doesn’t work into my lifestyle’ — if you don’t listen to that, it’s still not going to work. Funding is so tight, and it takes so much work to try and try again to get anything approved. Don’t waste your energy on something the client has already told you isn’t going to work.”
So while seat slope can seemingly be reduced to a simple number of inches, as with most seating & mobility factors, much more comes into play, from environmental needs to client goals, to the client’s clinical needs to the ones involving his or her lifestyle and daily tasks.
“I think there’s a lot of mystery around seat slope,” Phillips says, “and it’s more art than science.”
This article originally appeared in the August 2012 issue of Mobility Management.