|Author:||Ching, Tak-shing Congo|
|Title:||Biomechanical and biological consequences of cyclic compression on intervertebral disc : an in-vivo rat-tail model|
|Subject:||Hong Kong Polytechnic University -- Dissertations|
Spine -- Mechanical properties
|Department:||Jockey Club Rehabilitation Engineering Centre|
|Pages:||xv, 163 leaves : ill. (some col.) ; 30 cm|
|Abstract:||Low back pain is a common ailment affecting 60-80% of the population and a condition of high treatment and compensation cost. The majority of low back pain has been shown to be associated with intervertebral disc degeneration, which in turn has also shown to be related to mechanical loading on the intervertebral disc. In this study, we investigated the effects of static and cyclic compression on the biomechanical and compositional properties of the intervertebral disc using an in-vivo rat-tail model. In the current study, seventy-two male Sprague-Dawley rats were used and randomly divided into twelve groups (six rats in each group): one control group, three sham groups, two static compression groups and six cyclic compression groups. All rats, except those of the control group, had 2 pins inserted at the mid-transverse plane of the 4th and 5th caudal vertebral bodies. Rats in the control group were used as the baseline for the compositional analysis of normal disc whereas rats in the sham groups were used for studying the effects of pin insertion on both the biomechanical and compositional properties of the intervertebral disc. Rats in the static and cyclic compression groups were used for investigating the effects of mechanical loading on the biomechanical and compositional properties of the intervertebral disc. For the control and sham groups, no mechanical loading was applied to the intervertebral disc. Rats in the static compression groups were loaded with a constant stress of 690kPa, while rats in the cyclic compression groups were loaded with cyclic compressive stress of rectangular wave pattern (max~=940kPa and min~=440kPa) at 3 different physiological frequencies (0.5, 1.5 or 2.5Hz). Both static and cyclic compressive loading protocols were applied daily to the rats under analgesia for a period of 1 hour, starting from day 3 to day 17 after pin insertion. Other than 1-hour static/cyclic compression, no external compressive stress was applied to the caudal 4-5 disc and rats were allowed to move freely without restriction. Biomechanical measurements of the inter-pin distance, angular compliance and angular laxity of the caudal 4-5 intervertebral disc were performed in-vivo during the course of the experiment. All the rats were sacrificed at the end of the loading protocol and the intervertebral discs (caudal 3-4, 4-5 and 5-6 discs) were harvested for compositional analysis in-vitro. Total proteoglycan and collagen content were semi-quantified and chondrocyte density of the nucleus pulposus portion was counted. The results showed that except the cyclic compression group at 1.5Hz, all other groups had a significant decreased in angular compliance as compared to the sham group. Also, a significant increase in angular laxity was detected on the static compression group and cyclic compression at 0.5Hz. Moreover, the decrease in disc height in the static compression group was significantly greater than that in all other groups, whereas the decrease in disc height in the cyclic compression group at 1.5Hz was significantly smaller than that in other cyclic compression groups. On the other hands, the total proteoglycan content of the nucleus pulposus in the static compression group was found to be significantly less than that in all other groups. It was also found that both static and cyclic compression had no significant effects on the total collagen content and chondrocyte density of the nucleus pulposus. Moreover, there was no significant correlation (r2<0.2) between the biomechanical and compositional properties of the intervertebral disc. The findings suggest that applied mechanical loading could result in changes in both the biomechanical and compositional properties of intervertebral discs. These changes were comparable to those observed in the degenerated spine. The results also demonstrated that static compression was more harmful than cyclic compression, and the biomechanical and compositional response of the intervertebral disc on mechanical loading is frequency dependent.|
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