On low back pain: Identification of structural changes in system parameters for fatigue loaded intervertebral disc using PCA

This paper presents the background of low back problem caused by repetitive fatigue loading. We emphasize on mechanism of Intervertebral Disc (IVD) and conditions for which the disc does not recover its original status under repetitive work and cause low back pain. The objective of this study is to identify structural changes in system parameters for fatigue loaded intervertebral disc. Principal component analysis (PCA) is used for studying the behavioral change of spine against cyclic loading as a function of time. Percentage difference and similarity factor was calculated for the analysis. Specimens were applied with impulse testing to measure the stiffness and acceleration after fracture, augmentation and fatigue loading. The fatigue loading were 650N, 950N and 1150N at 5Hz for 1, 2, 3, 4 and 5 hours. 12 hours rest was given between different loadings. Based on PCA analysis, it is observed that IVD does not restore to original condition after 50 minutes of fatigue loading. In addition, if people set load at range between 30 to 50 minutes, vertebra discs cannot fully return to the normal position anymore depending on total load. Vertebra can support load as much as 0.5kN limited to 30 to 50 minutes. It implies that fracture may occur. Rest is very important in order to prevent the deformity and abnormalities of backbone discs. We found that in spine vertebral acceleration and displacement are dependent on the applied force.