**7.1 Haptic simulation of the finite element spine model**

Initially, without pressing the stylus button, the user can touch and explore the spine model since it is considered to be rigid throughout. Then, the user can control the probe to apply external forces in any arbitrary direction onto any vertebra by pressing the stylus button to observe the locomotion and study dynamic properties of the spine model. Figure 23 shows the haptic real-time simulation of the finite element spine model under lateral bending. During this real-time simulation, the displacement, rotation and deformation of the spine can be recorded and then input to the offline FEA application for further detailed stress/strain and deformation behaviour analysis of IVDs as well as vertebrae.
