Development of a novel FE model for investigation of interactions of multi-motion segments of the lumbar spine.

The spinal anatomy is composed of a series of motion segments (MSs). Although finite element (FE) analysis has been extensively used to investigate the spinal biomechanics with various simplifications of the spinal structures, it is still a challenge to investigate the interactions of different MSs. Anatomical studies have shown that there are major spine ligaments connecting not only single-MS (i.e., two consecutive vertebrae) but also spanning multi-vertebral bones or multi-MSs. However, the effects of the multi-MS spanning ligaments on the spine biomechanics have not been investigated previously. This study developed an FE model of the lumbar spine by simulating the anterior longitudinal ligaments (ALLs) in two portions, one connecting a single-MS and the other spanning two MSs, with varying physiological cross-sectional area (PCSA) ratios of the two portions. The spine biomechanics during extension motion were investigated. The results showed that on average, the constraining forces by the two-MS spanning elements were ∼18% of those of the single-MS ALL elements when the PCSA ratio was 50%, but the two-MS ALL elements also applied compressive forces on the anterior surfaces of the vertebrae. Decreases in intradiscal pressure were also calculated when the two-MS spanning ALL elements were included in the spine model. The multi-MS spanning ligaments were shown to synergistically function with the single-MS elements in spine biomechanics, especially in the interactions of different MSs. The novel lumbar FE model could therefore provide a useful analysis tool for investigation of physiological functions of the spine.