Noninvasive cumulative axial load may induce intervertebral disc degeneration-A potential rabbit model

Intervertebral disc degeneration (IDD) is considered to be the main cause of many spinal disorders; however, its underlying pathophysiology is not clearly understood. Recent studies indicate that excessive mechanical loading may serve a major role in the initiation of IDD. The aim of the present study was to explore the effect of noninvasive cumulative axial loading on the intervertebral discs of the lumbar spine using a novel rabbit model. Rabbits in the experimental group were placed into individual tubes specifically designed to force maintenance of an upright posture and were loaded with a heavy collar to increase the intradiscal pressure of their lumbar spine. Radiograph imaging and magnetic resonance imaging (MRI) was performed every 4 weeks to provide evidence of disc degeneration. At the end of the experiment, the animals were sacrificed and disc specimens were harvested for quantitative polymerase chain reaction and histological analysis. MRI results revealed significant and progressive reductions in the signal intensities of lumbar discs in the experimental group compared with the control group throughout the 14-week study period. The expression level of type I collagen was significantly increased and the expression levels of type II collagen and aggrecan were significantly decreased in the experimental group compared with the control group (P<0.05). Histological examination revealed marked structural changes in the experimental group, including fibrocartilage-like tissue ingrowth and accelerated fibrotic changes of the nucleus pulposus. The results of the present study indicate that noninvasive cumulative axial load is able to induce accelerated degenerative changes in rabbit lumbar discs, which may provide useful information for the establishment of a novel animal model of IDD for the research of IDD in humans.