Subject-Specific Spinal Alignment Analysis in the Supine Position

The spine is stabilized by the intervertebral discs themselves and the surrounding soft tissues such as the ligaments and muscles, which are prone to fatigue injuries under prolonged malpositioning. The humans spend about one-third of their lives lying on the bed. Thus, it is essential to maintain a good spinal alignment in the supine position. However, direct measurement of the forces in the body in vivo is possible only in exceptional circumstances. Owing to the varieties of back shapes and body figures across individuals, it is difficult to provide a subject-specific analysis to simulate the spine alignment while lying supine on the mattress. The study reconstructed an existing whole body CT scan data into a three-dimensional model with different kinds of tissues. A generic whole body finite element model was built and each element was assigned a tissue by point-in-polyhedron tests. Secondly, to generate a subject-specific FE model, the study utilized Kinect to capture depth images which were stitched into subject’s whole body point cloud. Surface deformation from CT to subject’s model was determined with non-rigid registration （CPD）. Inner tissue deformation was determined with kernel regression following CPD’s assumption. A subject-specific FE model was then created. Together with the mattress model formed in the software, the study has succeeded in analyzing spinal alignment during supine with validation. The results showed that forecasted subjects’ weight difference with that of real weight were all less than 3 kg, which were accounted for less than 10% of their real weight. The FE analysis results revealed that the study was able to forecast the trend of angle difference around neck and lumbar across different mattress. The study, however, tended to underestimate the deformation of spine, while the possible reason and solutions were also proposed in the study. The study provided a three-dimensional customized process to spinal analysis without invasive technique or radiation. It was helpful to gain insight of spinal alignment during supine with different mattress for different people. The study would help to the development of mattress and the diagnosis of spine.