Development and Biodynamic Simulation of a Detailed Musculo-Skeletal Spine Model

Abstract

The spine is one of the most important and indispensable structures in the human body. However, it is very vulnerable when suffering from external impact factors, resulting in spinal diseases and injuries such as whiplash injury, low back pain. In literature, spine models are extensively developed using either finite element or multi-body methods to find feasibly suitable solutions for treating these spinal diseases. However, these models are mainly used to investigate local biomechanical properties of a certain spinal region and do not fully take into account of muscles and ligaments. Hence, the aim of this thesis is to develop an entirely detailed musculo-skeletal muti-body spine model using LifeMOD Biomechanics Modeler and then simulate biodynamic behavior of the spine model in a haptically integrated graphic interface. Initially, a default multi-body spine model is first generated by LifeMOD depending on the user's anthropometric input. Then, a completely discretized spine model is obtained by refining spine segments in cervical, thoracic and lumbar regions of the default one into individual vertebra segments, using rotational joints representing the intervertebral discs, building various ligamentous soft tissues between vertebrae, implementing necessary lumbar muscles and intra-abdominal pressure. To validate the model, two comparison studies are made with in-vivo intradiscal pressure measurements of the L4-L5 disc and with extension moments, axial and shear forces at L5-S1 obtained from experimental data and another spine model available in the literature. The simulation results indicated that the present model is in good correlation with both cases and matches well with the experimental data which found that the axial forces are in the range of 3929 to 4688 N and shear forces up to 650 N. To enhance more realistic interaction level between users (such as trainers, clinicians, surgeons) and the spine model during real-time simulation, a haptics technique is successfully integrated into a graphic environment named HOOPS in this research. Based on this new technique, the exploration process of the users for the spine model becomes much more realistic since the users can manipulate the haptic cursor to directly touch, grasp and feel geometric shape as well as rigidity of the spine through the force feedback of the haptic device. Moreover, they can even apply external forces in any arbitrary direction onto any certain vertebra to make the spine move. In such versatile simulation interface, the users can quickly and more conveniently study the locomotion and dynamic behaviour of the spine model. Overall, this thesis has developed a bio-fidelity discretized multi-body spine model for investigating various medical applications. This spine model can be useful for incorporation into design tools for wheelchairs or other seating systems which may require attention to ergonomics as well as assessing biomechanical behavior between natural spines and spinal arthroplasty or spinal arthrodesis. Furthermore, the spine model can be simulated in the haptically integrated graphic interface to help orthepaedic surgeons understand the change in force distribution following spine fusion procedures, which can also assist in post-operative physiotherapy.