Commercial donut pillows are used during lengthy surgical operations. With the patient anesthetized, the multiple pressure points on the head and wrinkling of the skin cut off blood circulation in the face, which leads to facial decubitus ulcers .
Cellular type materials such as foam, which are used in these pillows, are very effective in reducing pressure points by transferring pressure into shear forces . In a similar way to surgical pillows, these materials are used to reduce foot pain due to plantar pressure in foot orthotics .
However, these same shear forces lead to wrinkling of the skin which generates sores. These shear forces are related to shear stress in the pillow. Pressure normal to the pillow surface is related to normal stress in the pillow, which also leads to soring. Thus, the optimal pillow design, which reduces sores due to pressure points and wrinkling, would be characterized by the design where optimal values of the normal and shear stress are obtained .
In a previous study , a surgical pillow design was developed which implemented foam wedges. The angle these foam wedges made with the transverse plane was determined to be the angle that gave minimal values of the normal and shear stresses. Thus this new pillow design reduced pressure sores as well as sores due to wrinkling of the skin.
The use of foam wedges has some fundamental disadvantages. Chief among these disadvantages is that the wedges have planar surfaces which do not match the curvature of the human body well. This tends to make the wedges uncomfortable and ineffective. In addition, the manufacturing of small wedges which then have to be connected to the main pillow structure is cumbersome and inefficient.
In this study, a new pillow design was developed which is based on the contour of the patient’s body to generate supportive surfaces that not only match the patient’s shape exactly but which minimizes normal and shear stresses.