Seating system categories The previous sections discussed primary and secondary seating surfaces as well as seated angles. Once the required support surfaces and angles have been determined, they are matched with a specific category of seating system, either linear, contoured, or molded. Linear systems Linear systems have linear, or planar (flat), surfaces (Figure 10). The seat and back are flat, as are components such as lateral trunk supports and lateral pelvic supports. Linear seating systems are often used with pediatric clients and clients who require minimal to moderate postural support and control (Furumasu, 2018). Linear systems are generally less expensive than other seating systems. They also accommodate growth best, as only overall seat and back width and depth need to be changed, rather than other, more discrete measurements found in a contoured or molded system. Figure 10: Linear Seating System
and seat depth will not match that individual’s needs. Contoured systems also provide less room to accommodate growth. Figure 11: Contoured Seating System
Note . From ROHO, Inc., n.d., retrieved from https://roho.com/category/products. © ROHO, Inc. Reprinted with permission.
Molded systems Molded seating systems are custom-molded to the client to match body surface contours (Figure 12). These systems may be made up of one or two pieces; most secondary support surfaces, such as lateral trunk supports, are molded into the seating system itself. Molded systems are generally employed for clients who have significant orthopedic asymmetries that cannot be adequately supported in another seating system, for clients who need significant stability and postural support, and/or for clients who are at high risk for pressure injuries. Molded systems provide intimate body surface contact and significant pressure distribution. This provides maximum stability, orthopedic alignment, postural control, and pressure distribution for comfort and to minimize risk of pressure injuries. Figure 12: Molded Seating System
Note . From Stealth Products, Inc., n.d., retrieved from http://www.stealthproducts.com. © Stealth Products, Inc. Reprinted with permission.
The disadvantage of linear systems is that less of the body surface contacts the seating surface. This reduces pressure distribution, which can increase risk of pressure injuries and decrease comfort. Comfort is important because a client who is uncomfortable does not sit in his or her seat as long. This may in turn require a caregiver to transfer the client out of the wheelchair and into bed or another alternative position. Less seat contact also means less stability, which is very important for functional tasks. Finally, when muscles are well-supported, they tend to relax. If a muscle group is not in contact with the seat (i.e., the mid-back), those muscles are more likely to spasm, leading to pain (Sparacio, 2018). Contoured systems Contoured systems have generic contours built in to increase surface contact with the body (Figure 11). These generic contours may be found in the seat, back, and components. Contoured systems are often used for clients with moderate need for support, postural alignment and control, stability, and pressure distribution. Seating systems often combine linear and contoured components. Most wheelchair cushions are contoured. The advantage of contoured systems is that surface contact is increased (Sparacio, 2018). This can increase pressure distribution to reduce the risk of pressure injuries and increase comfort. This contact can promote muscle relaxation and may also increase stability and function. The disadvantage of contoured systems is that the contours are generic. A common example of generic contours is an automobile seat. These contours are more comfortable than the flat benches still found on many school buses, but the contours of an automobile seat may not match the driver’s body shape. For example, if the driver is shorter than a standard car driver’s seat, the contours
Note . From Ottobock, 2013, retrieved from http://www.ottobockus.com. © Ottobock. Reprinted with permission. The disadvantages of a molded system are in most cases cost, time and expertise required, and lack of growth accommodation (Sparacio, 2018). Custom-poured liquid foam (foam-in-place) is less costly and time consuming. The support provided is not as strong as support provided by other molded systems, but this type of mold can be modified or re-poured for growth or condition changes. Molded seating systems are often bulky and retain heat, and transfers are more difficult. Weight, materials, and ventilation vary among systems. A less-than-optimal mold can be uncomfortable at best and, at worst, can worsen orthopedic limitations or cause pressure injuries. Because the system matches the client so precisely, any change in linear growth or weight can create a problem.
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