Biomechanical Effects of Spinal Flexibility and Rigidity on Lumbar Spine Loading: A Finite Element Analysis Study

Objective: The effects of spinal rigidity correlate positively with low back pain. Although spine flexibility has also been considered important for preventing stress-related lumbar disorders, the effects of spinal rigidity on mechanical stress during lumbar motion have rarely been reported. Methods: A biomechanical investigation and finite element analysis were conducted to elucidate the effects of flexibility of the lumbar spine. We created two kinds of rigid and flexible spine models by changing the material properties of the ligaments and discs. A hybrid loading condition was applied and the maximum stresses on the discs and pars inter articularis were computed. Results: The FE analysis, in the rigid spine models, the range of motion decreased to about 80%, while in the flexible spine models it increased to about 110% that of the intact model. The pars and disc stress increased in both rigid models. Conclusions: Biomechanically, both pars stress and disc stress increased in the rigid spine; a flexible spine is important for preventing stress-related disorders such as lumbar pars stress fracture and degenerative disc disease. Thus, flexibility of the spine is beneficial for preventing low back pain by reducing the lumbar loading.