Seating & Positioning

Skin that bears weight in a wheelchair lives in hostile territory. Pressure, shear, moisture and heat combine to create ideal conditions for the development of decubitus ulcers. In fact, a landmark study found that at least 20 percent of wheelchair users have a skin breakdown in any one year, which means that virtually every user is likely to encounter a skin problem within four to five years.

Ottobock specializes in seating and positioning products for users at high risk for skin-integrity issues. You are considered at high risk of skin-integrity issues if any of three statements is true as relates to sitting in your chair.

You have a history of redness and/or the presence of open wounds on your seated surface.
You cannot do an effective, independent weight shift on a consistent basis.
You have impaired sensation and don't check your skin daily and don't practice consistent weight shifts.
The good news is that most pressure ulcers—localized injuries to the skin and/or underlying tissue, usually over a bony prominence—are preventable. For that reason, anyone who spends their days in a wheelchair needs three types of skin protection as it relates to their wheelchair seating system.

Pressure in this case is the force on tissue pinched between bone and the external support surface (wheelchair upholstery or wheelchair seating surface). It can cut off the supply of blood and oxygen to an area and eventually cause tissue to break down. Pressure management relies on physics to assist with defending against pressure ulcers. You can reduce peak pressure by spreading the weight over a larger area.

Pressure = Force (body weight) / Area (weight-bearing area)

When you are seated on a firm, flat surface, all of your weight rests on bones on the underside of your pelvis (ischials), making you a potential candidate for decubitus ulcers.

To reduce this peak pressure it might be a good idea to redistribute or share this concentrated load over the whole of your underside surface for example your buttocks, undersurface of thighs and don't forget your feet if possible. Your back may also be able to take a lot of load while you are sitting. Your health care professional should help you with this at the time of your assessment and prescription.

Because those bony curves are your low points, a cushion improves load bearing by allowing you to sink into it as much as 2.5 inches without hitting bottom. Armrests and footplates at the proper height can bear some of your weight. So can back support that matches the curve of your spine.

Shear, which damages tissue with distorting forces, refers to the forward-and-back motion of the ischials against tissue under pressure. For active people, recesses or a liquid layer under the ischials allow movement of bony prominences which are intended to reduce high shear forces.

People who are active or overweight or who have certain medical conditions generate a lot of heat and may perspire heavily on support surfaces. This can be more than uncomfortable: it can create a climate that can help lead to decubitus ulcers. Cushions that allow air and moisture to pass through help skin stay cooler and thereby contribute to a healthier seating environment.