ABSTRACT
Incorrect body support and positioning during sitting, working and sleeping often cause low back pain. The fact that people spend a large part of their lives in bed justifies the need for an objective and scientifically sound method to determine the right sleeping system for each individual.
A parametric finite element model of the combination individual-mattress was developed to predict the curvature of an individual’s vertebral column when lying on a specific sleeping system. The resulting model represents the spine as a succession of quadrangular elements, each with its specific simplified geometric and material properties. The rest of the human body is modeled by rigid skeleton elements linked by joints and surrounded by soft tissue.
Simultaneously two experimental setups were used to validate the model by measuring vertebral positions during bed rest. The first setup is a camera system detecting reflecting bullets which are mounted a) on the spinous processes (lateral recumbency) and b) on pins which are pierced through the mattress (posterior recumbency). A second experimental setup was built to perform indirect but fast measurements by measuring not the position of the spinous processes, but the position of the mattress surface. Both measurements and F.E. analyses were performed for 30 people on 5 different mattresses. It was possible to decide whether and where mattress stiffness had to be adjusted. Further one could decide which mattress (out of 5) offered the best supporting qualities based on F.E. predictions. A numerical shape prediction of the vertebral column was not yet possible, which justifies the need for more reliable (e.g. 3D) analyses.
