Finite Element Modeling and Simulation of Degeneration and Hydrotraction Therapy of Human Lumbar Spine Segments

A large percent of population is affected by low back pain problems all over the world, starting from the degeneration of the lumbar spinal structure, caused generally by ageing and mechanical overloading. If the degeneration is not too advanced, surgical treatments can be avoid, by applying conservative treatments, like traction therapies. Dry traction is a well-known method, however, often happens that instead of the traction effect and stress relaxation, the compression increases in the discs due to muscle activities. This verifies the importance of the suspension hydro-traction therapy, where the muscles are completely relaxed. The aim of this study was doubled: to model and simulate numerically the age-related and accidental degenerations of lumbar functional spinal units (FSU) and to simulate the mechanical answer of the more or less degenerated lumbar segments for the hydro-traction treatment, by using FE method. The basic question was: how to unload the disc to regain or improve its functional and metabolic ability. FE simulations of the mechanical behaviour of human lumbar FSUs with life-long agerelated and sudden accidental degenerations are presented for tension and compression. Compressive material constants were obtained from the literature, tensional material moduli were determined by parameter identification, using in vivo measured global elongations of segments as control parameters. 3D FE models of a typical FSU of lumbar part L3-S1 were developed extended to several nonlinear and nonsmooth unilateral features of intervertebral discs, ligaments, articular facet joints and attachments. The FE model was validated both for compression and tension, by comparing the numerical calculations with experimental results. The weightbath hydrotraction therapy decreases pain, increases joint flexibility, and improves the quality of life of patients with cervical or lumbar discopathy. Numerical simulations were investigated to clear the biomechanical effects of hydrotraction treatment of more or less degenerated segments to improve the efficiency of the non-invasive conservative treatment. László Oroszváry, Márta Kurutz 2