Biomechanical effects of a lumbar support in a mattress

Abstract

For many patients with chronic low back pain, the lack of sleep and sufficient rest period that allows some relaxation is a major obstacle to a good quality of life. During sleep periods, neuromuscular activity is at a minimal level. The major factor influencing the forces on the body, and particularly the spine, is gravity. The force of gravity is sufficient to deform soft tissues when the body is resting on a mattress. Thus, the goal of this study is to measure the contact pressure forces acting on the spine with and without an inflatable support in various experimental conditions. Our hypothesis is that a lumbar support will distribute the force of gravity more uniformly over the pelvic, lumbar and thoracic areas, maintaining the lumbar lordosis, in a supine posture. In this study, 10 participants were tested when lying supine in six separate experimental conditions. These conditions varied according to the surface (no mattress, foam, mattress) and the fact that the support was inflated or not. The dependent variable measured was the contact pressure. It was measured using a pressure sensor mat (Tekscan). When the cushion was inflated the distribution of contact pressure in the different areas (pelvic, lumbar and thoracic) was modified. The comparison of the mean forces revealed that when the cushion was not inflated, the pressure distribution was mainly localized in the pelvic area. After the cushion was inflated, a significant decrease of contact pressure in the pelvic region and a significant increase in the lumbar area were observed. Our results confirm the hypothesis that a lumbar support inserted in a mattress allows a more homogenous distribution of contact pressure over the pelvic, lumbar and thoracic areas during supine posture. The use of an inflatable cushion favouring a transition of the contact pressure from the pelvic to the lumbar region could potentially limit unfavourable compressive and shearing forces acting on the lumbar spine.

Figure 1a

Illustration of the overall effect of contact pressure redistribution in all three areas analyzed without the lumbar support inflated for one subject and one trial. The darkest area represents the highest contact pressure recorded. A lateral view of the skeleton was superimposed on the contact pressure measurement to illustrate the location of the inflatable cushion and the subject’s specific position. The triangle illustrates the PSIS landmark.

Figure 1b

Illustration of the modification in the intensity of contact pressure in all three areas analyzed with the lumbar support inflated for the same subject and the same trial. One can observed the reduction of contact pressure in the pelvic area and the increase of contact pressure in the lumbar area.