**7.3 Investigating dynamic properties of the spine model under external haptic forces**

Since the finite element spine model for the haptic simulation is represented with beam element which is in fact highly simplified, it is difficult to describe precisely the dynamic properties of the real spine. Compared to this finite element spine model, the detailed musculo-skeletal multi-body spine model developed in LifeMOD can provide better information of biodynamic behaviour of the spine. Since LifeMOD software takes account of other components (such as head, ribcage, muscles, ligaments so on), the locomotion of the spine model will become much more realistic. Furthermore, by simulating the spine model in a haptically integrated graphic environment, the users (such as surgeons, trainers) can quickly and conveniently observe the locomotion as well as gain insight into the dynamic behaviour of the spine.

Development of a Detailed Human Spine Model with Haptic Interface 191

In general, we have presented the process of modelling human spine. Initially, a beam FE spine model for haptic interaction is built based on a solid FE spine model, which is created in offline finite element analysis software. Although there are some limitations on not fully taking into account soft tissues, this beam FE model is able to simulate global dynamic behaviour of the whole spine, Subsequently, an entirely detailed musculo-skeletal mutibody spine model using LifeMOD Biomechanics Modeler is completely developed to solve the limitations aforementioned and reliably validated by comparing simulation results with experimental data and in-vivo measurements. Moreover, to enhance more realistic interaction between users (such as trainers, clinicians, surgeons) and the spine model during real-time simulation, haptic technique is integrated into a graphic interface. Based on this, exploration of the spine model becomes much more realistic since the users can manipulate the haptic cursor to directly touch, grasp and even apply external forces in any arbitrary direction onto any vertebra to observe the deformation of the spine. In such a simulation interface, users can quickly and more conveniently study the locomotion and dynamic

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**8. Conclusion** 

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**9. References** 

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The long-term goal of this study is to develop a haptically integrated simulation platform for investigating post-operative personal spine models constructed from LifeMOD. The first step in this study is to develop a haptic interface for a detailed normal spine model whose dynamic properties are obtained from LifeMOD. Figure 26 illustrates the analysis of some dynamic properties of the spine when applying force on vertebra T1 in x-axis direction.

The next step in the study is to develop a post-operative detailed spine model. The operation conducted on the spine model can be spinal fusion or spinal arthroplasty. By using this haptically integrated graphic interface, assessing biomechanical behavior between natural spines and spinal arthroplasty or spinal fusion becomes more convenient. This will help orthepaedic surgeons understand the change in force distribution following spine fusion procedures, which can also assist in post-operative physiotherapy. In addition, the surgeons can gain useful insight from this system in the planning of surgery to correct severe scoliosis. Different designs of rods and braces can for example be experimented with using this virtual environment. It is also considered that this system may assist physiotherapists and other practitioners when designing cushioning and supports for wheelchair-bound and other clients suffering from asymmetric spinal disorders.

Fig. 26. Analyzing translational properties of the spine model under lateral force on T1
