The biomechanical and biological effects of conservative treatments on simulated intervertebral disc degeneration using an in-vivo rat-tail model

Abstract

Low back pain (LBP) is a common musculoskeletal problem that affecting more than 50% of population in the world. Degeneration of intervertebral disc has been found to be associated with LBP. Thus, regeneration of degenerated disc may be a potential treatment for LBP. Electro-acupuncture (EA) and traction have long been used for LBP treatment. They have been found to improve pain level, physical activity and functional status and induce biochemical changes in the disc. However, their effects on degenerated disc are still unclear. Thus, the purpose of this study was to study the biomechanical and biological effects of EA and traction on degenerated disc in an attempt to explore whether they could reverse disc degeneration. An in-vivo rat-tail model was adopted and there were two stages in this study: 1) to establish a disc degeneration model, and 2) to investigate the effects of EA and traction on the degenerated disc. In the first stage, static compressions of different magnitudes (11N or 17N) and durations (Ihr or 24hrs per day) were applied to rat 8-9 caudal disc for two weeks. The loads were then removed for following three weeks. In-vivo disc height and angular compliance, laxity and passive range of motion (ROM) as well as in-vitro morphological changes were examined. Significant decreases in disc height, angular laxity and ROM were found after continuous compressions (24hrs per day) of either 11N or 17N. Further decreases in the biomechanical properties were observed after the three weeks resting period. Significant decrease in disc height during resting period was seen after UN continuous compression only. Degenerative morphological changes, including irregular nucleus pulposus, spindle-like nuclear cells, disorganized annulus fibrosus and inward bulging of inner annulus, were observed after the continuous compression. For the 1 hour daily compression, transient increase in disc height and decrease in angular laxity and ROM as well as normal disc structures were found. Continuous compression of 11N was finally adopted as the disc degeneration model for the second stage of the study. In the second stage, simulated EA of different frequencies (2Hz or 100Hz) or traction of different modes (static or intermittent) and magnitudes (1.4N or 4.2N) was applied to rat caudal 8-9 disc with simulated degeneration for three weeks. In-vivo biomechanical properties and in-vitro morphological changes of the disc were examined. Both EA and traction could not demonstrate any effects in restoring the adverse changes induced by the continuous compression. Nevertheless, the effects of EA were found to be frequency dependent while the effects of traction were observed to be traction magnitude dependent. The disc height further decreased after high frequency EA and traction of high magnitude, but maintained after traction of low magnitude. Morphological analysis showed that EA of high frequencies induced further adverse changes. In this study, a rat-tail disc degeneration model was established which could be used for studying the effect of therapeutic interventions. The transient increase in disc height following daily compression indicated daily short duration compression might have beneficial effect on the disc which deserves for further investigation for its clinical value. Both EA and traction were ineffective to restore the degenerative changes induced by continuous compression. Moreover, further degenerative changes were seen following EA of particular frequency and traction of certain loading magnitude might be able to slow the degeneration process. Attention should therefore, be paid in selecting suitable parameters of these treatments for LBP patients with disc degeneration.