Instability of the lumbar spine due to disc degeneration. A finite element simulation

Low back pain, which most common cause is degenerative disc disease, currently represents a serious problem due to its socio-economic repercussions. Different factors are involved in the degenerative process, being the most common: the loads on the spine, repeated flexion movements and individual genetic characteristics. Nowadays, there is no agreement on whether instability is the main cause of low back pain, or only one reason among many, and on whether increased spinal mobility, associated with instability, occurs either locally or at the lumbar spine as a whole. In this work, the simulation of disc degeneration is based on a finite element model of lumbar spine. A parametric study based on mechanical properties was established, for each lumbar spine movement, by evaluating the disc degeneration in 10% steps, from healthy disc to maximum degeneration. The results show as general trend a progressive mobility increase as the disc degeneration level raises. As main conclusion, disc degeneration causes increased mobility at all vertebral levels, with moderate values for incipient degeneration and much higher values for advanced degeneration, affecting more severely to the levels closest to degenerated disk. The great mobility increase detected at L5 could explain the instability detected as a clinical symptom.