Multisegmental fusion of the lumbar spine a curse or a blessing?

Abstract

Excessive mechanical load of the spinal structures during unfavorable movements in daily life can lead to degenerative damages especially of the lumbar spine. If the affected structures are damaged in such a way that conventional therapy does not improve the situation, often a surgery is unavoidable. One surgical method is the fusion of the affected spinal segments. In particularly difficult cases, the fusion may even extend over more than one functional spinal unit. An appropriate method for the estimation of the biomechanical effects of such interventions to adjacent vertebral segments is the computer simulation. This paper presents a 3D-MultiBodySimulation(MBS-) model of the lumbar spine with realistic surfaces and included intersegmental discs as well as ligamental structures. For these elements the physical behavior like force-deformation relations and characteristic curves for the torque-angle relations are formulated. The facet joints are modeled as cartilage, in order to simulate the contact between the corresponding articular surfaces. With this simulation, the effects of mono- and multisegmental fusions to the lumbar structures can be analyzed. The comparison of the simulations shows a redistribution of loads within the intervertebral discs. In the simulation case of monosegmental spinal fusion, the intervertebral disc below the fused segment are more loaded than in the simulated healthy state. The validation of the model was carried out by comparing the results with FE-simulations, various of vitro experiments and experimental data from biomedical literature.

Keywords

• mbs model
• monosegmental fusion
• multi-segmental fusion
• adjacent vertebral segment loading
• load redistribution