Physics, Risks, Assessment & Management of a Long-Time
- By Laurie Watanabe
- Apr 01, 2012
Once upon a time, shear was one of the biggest positioning foes for seating providers and clinicians. But over time, conversations about shear have somewhat waned, largely because of improvements in tilt & recline systems.
Nevertheless, many clients remain at risk for shear — and may not even be aware of it. Knowing the risk factors and how to prevent or at least manage them can therefore make a significant difference in overall skin health, client activity and independence.
The Physics of Shear
Mosby’s Medical Dictionary (2009) defines shear as “an applied force or pressure exerted against the surface and layers of the skin as tissues slide in opposite but parallel planes.”
That force can damage blood vessels and prevent or reduce blood supply to underlying tissues, leading to tissue death.
For wheelchair users, that force can often occur as part of the repositioning process.
In her presentation “What We Forgot We Knew About Tilt& Recline,” Stephanie Tanguay, OTR, ATP, clinical education specialist at Motion Concepts, discusses the history of tilt and recline systems, including designs that made recline systems prone to shearing forces.
“Historically, pivot points used to be level with the seat rails,” Tanguay says. “The majority of manual recliners in the industry today are still built with the pivot point of the recliner at the level of the seat rail. You have to always think about the distance of the pivot point in proximity to the pivot point of the body. The pivot point of the equipment and the pivot point of the body are really what dictates a lot of this.”
In her presentation, Tanguay notes, “For decades, manual and power reclining chairs utilized a pivoting point from which the back canes moved to open (recline) and close (sit upright), which was level with the seat rail of the chair. The shearing effect of the back support moving against the seated person’s skin was related to this lower pivot point.
“The effects became more severe as seat cushions were added to the wheelchairs, raising the consumer’s body (and their hip joint, their ‘pivot point’) further away from the pivot point of the reclining wheelchair. In this scenario, shear moves against the seated consumers’ back and sacrum as they recline.”
Tanguay explains, “When you sit on any surface, if you move from sitting upright to reclining, the mechanical structure has a pivot point, and the patient’s body has a pivot point. When we recline, the hip joint is the body’s pivot point, and then there’s the pivot point somewhere on the wheelchair, manual or power. The closer we can keep the pivot points together, the better it is.”
The Revolution of Recline
Tanguay notes that LaBac’s raised pivot recline created in the late 1980s was a turning point in the battle against shear.
“(LaBac is) really the first company that I have any recollection that did that, but it is the industry standard now,” Tanguay says. “Everybody’s power recline system has a three-inch raised pivot point to it.”
That three-inch measurement, she adds, is a reference to the thickness of popular cushions at that time.
“With a pelvis sitting on it, you were basically looking at about three inches sitting above the seat rail, and that’s where that magic three-inch raised pivot point came from,” she explains. “When you put the cushion on top of the seat, you’re pivoting close to the top of the cushion. And that’s a way of trying to get the body and the chair’s pivot points closer together.”
That raised pivot point, however, didn’t solve the entire shear problem. So to complement it, the sliding back was born.
“The back moves on some sort of track or glide blocks,” Tanguay says. “It moves with the body.” The gap below the back, she adds, is to give the back enough room to move downward while remaining in contact with the client’s body.
Another factor to consider, Tanguay adds, is the client’s clinical condition.
“We have to keep in mind the patient’s range of motion,” she says. “If you have tight hamstrings, for example, reclining might be difficult, but reclining in elevating legrests might really be difficult because tight hamstrings are going to aff ect your knees as well; they’re going to aff ect your hip joint. We’re prescribing equipment that moves; we have to know about the movement of the body to make sure it’s accommodated properly.”
And finally, it’s important for all the members of the seating & mobility team to be aware of how their component and accessory choices could raise shear risks.
“What we’re most worried about is shear from recline, where the pivot point is, how much the back is sliding,” Tanguay says. “And then there are all the things that people do to the seating support systems that also skew that.
“Manufacturers are building power recline with raised pivot points to address shear, but then people put on really thick backs that move (the client’s) pelvis. You can move somebody anterior, away from the pivot point of the recline system, and you can have a cushion that is very thick that raises them up and away from the pivot point as well. If my cushion is too thick, I’m high up above it; if my back is too thick, I’m farther forward from it. We can also see that happen with someone who has a lot of soft tissue on their body.”
Shear Risk During Transfers
Less active wheelchair users who don’t reposition themselves or perform weight shift s often enough are commonly thought to be at higher risk for developing pressure ulcers.
Shear injuries, however, can occur even with very active wheelchair users who regularly move among different seating surfaces.
In fact, making those transfers can present elevated risks.
“It’s going to depend on the quality of their transfers,” Tanguay says. Many of these transfers will be lateral, and ideally the client is able to entirely lift himself or herself up. “Or at least when I get to whatever surface I’m transferring onto, if I can do a little bit of a pushup and my tissue isn’t displaced, it would be better,” Tanguay adds. “The people who really struggle with this are people who drag themselves. If you use a sliding board, you’re displacing tissue on the sliding board. So people slide across it, or they use it like a bridge and do little hops across it. So people who displace tissue or don’t even use a sliding board, but just transfer from their bed to their chair, are dragging their tissue across the tire, and they drag across the seat surface. You’ve always got therapists looking for more slippery covers so people can slide easier, but anything that’s involving sliding, if you’re not clearing the contact of your weighted tissue, the chances are that you’re occluding some bloodflow because you’re displacing tissue.”
Adding to that, Tanguay says, is the fact that many clients can’t feel that they’ve displaced tissue because they’ve lost some or all sensation.
“They don’t even know when they’ve done this,” Tanguay says, “which can be very problematic for them.”
Jean Sayre, OTS, COTA/L, ATP, CEAC, is the director of clinical education for The Comfort Company. Because of the prevalence of shear, she says, she makes the assessment for it a part of all client evaluations.
“When I’m doing my evaluation, the first question I ask is what they do throughout the day, from the time they get up in the morning to the time they go to bed,” Sayre says. “I even ask them how they’re positioned in bed.”
Sayre’s frequent work in the home accessibility field has caused her to look for shear risk in a number of everyday locations and scenarios.
With transfer benches, for example, she says, “I see a lot of chafing, a lot of abrasions occurring from that shearing effect. A lot of clients I work with are also having neuropathy and are diabetic, so they have to be very careful with their skin integrity, which is already compromised.”
Though shear is perhaps most often talked about in conjunction with seating systems, Sayre makes sure to consider all other possibilities.
“I think about footrests,” she says. “I think about shearing of the feet — plantar shearing, which is breakdown on the bottoms of the feet. We’re so concerned, obviously, with seating & positioning that I think the feet are forgotten about a lot of times. That happens a lot with (clients with paraplegia) and younger, active patients: You have shearing that occurs in the feet, so you have to make sure you’re taking care of proper positioning of the lower extremities and the footrests.”
Looking at All the Possibilities
Figuring out what activities and environments are causing shear can be tricky, particularly among active clients.
As an example, Sayre cites a veteran she once worked with.
“He purchased a Camaro and was so excited,” Sayre says.
He also showed signs of injuries to his skin.
“I was very baffled, because we couldn’t figure out where the redness was coming from,” Sayre says. “I actually had to do a skin inspection to see where the redness was, and it looked like a little abrasion.”
Sayre asked him to bring his Camaro to the VA and then had him perform transfers in and out of his new car as she observed.
“That’s when I noticed he was dragging across his (car) seat, and also his seat had some piping and seams,” Sayre says . “That piping on the edge is what he was dragging across, so he was shearing across it.”
The solution: “ We had to modify his seat with a low-profile air cushion to protect him from the seat as he was going across the surfaces.”
Sayre also noted he had some difficulties transferring his chair in and out of the car, and suspected he may have also experienced some shear while transferring on and off toilet seats.
“Even though they’re able to do their own pressure management,” she says of active clients, “they’re not being able to prevent that shear.”
Educating Consumers About the Risks
Ultimately, educating consumers about shear — what it is, its risk factors and how to reduce them — is critical. And seeing is believing.
Tanguay says she likes clinicians and providers to take lateralview photos of clients when they’re sitting up and when they recline.
“You can really see where everything moved,” she explains. “Some people are so displaced even with one recline cycle that they have to be repositioned every time they recline and sit back up.”
Sayre says she promotes sliding transfer benches for many of her clients: “You get yourself onto the seat — swivel or non-swivel, depending on where the transfer is occurring — and then the gravity will take effect, so you pull yourself over, and it locks into place. You’re not sliding across, so you’re preventing that shearing, abrasion and friction.”
She’s also recommended gel covers for toilet seats, since gel’s viscosity (along with air-filled cushions) helps to prevent shearing. And for clients who are more static, she says, “That’s when you can use manual or power lift s instead of pulling them across the bed.” Sayre adds that transfer or repositioning bed sheets are also designed to reduce potentially dangerous friction.
But while providers, clinicians and caregivers may be naturally more inclined to worry about shear among sedentary clients, Sayre says active wheelchair users — with their multiple transfers every day in and out of cars, onto and off bathroom equipment, onto and off of different pieces of furniture, etc. — also need to know about shear.
“Just from my experience, I feel that they’re at higher risk for shearing than some of the static patients,” she notes.
Education for all wheelchair users, therefore, is important.
“I’ve worked with people who transfer into the chair, but can’t get all the way back,” Tanguay says. “They put themselves into tilt, and they tilt back to let gravity push them back into the chair.”
Consumers who don’t understand shear forces — but who are resourceful in other ways — may end up problem-solving themselves into dangerous situations.
Tanguay remembers a power chair user who would drive up to a wall, then put her feet against the wall. “Then she would drive closer to the wall to use the force of her feet on the wall to shove herself back into the chair,” she says.
All the more reason to learn as much as possible about a client’s everyday activities when evaluating for shear. Because as Sayre says, so many things “could possibly be a piece of the puzzle.”
This article originally appeared in the April 2012 issue of Mobility Management.