The analysis of mechanical behaviour of spinal column is until now still a challenge, in spite of the great amount of research which has been conducted over the last years. It is a particularly complex structure considering number of components, their shapes and mechanical characteristics. The objectives of the presented investigations are to understand the mechanisms of the mechanical behaviour of the spine structure and the role of its components, as well as the factors of its dysfunctions as scoliosis discopathy, spondylolisthesis. Also some mechanical effects of surgical interventions by total disc replacement is considered. To account for the 3D character of the spine system including vertebrae, discs, ligaments, muscles etc. the finite element method (FEM) formulation was used throughout the paper. Some specific features of the structure are included in the models as non-conservative loads and muscular tension control performed by the nervous system. The finite element method together with CAD programs and experimental validation was used in investigations of a new type of artificial disc for lumbar spine. The stress analyses were performed for the prostheses being in clinical use and for some original new designs. The conclusions concern most important determinants of the mechanical behaviour of the system and the quality of the intervertebral disc prosthesis.