Prolonged upright posture induces degenerative changes in intervertebral discs in rat lumbar spine

Study Design. Both forelimbs of rats were amputated, and these rats were kept in the custom-made cages that kept the rats in prolonged upright posture. Pathologic changes were observed in the lumbar spine at different time points after the surgery. Objective. To investigate the effect of upright posture on intervertebral discs of rat lumbar spine. Summary of Background Data. Previous studies have shown that increased axial forces on the spine can decrease the height of the intervertebral disc, but there are no data to indicate whether or not long-term and repeated assumption of the upright posture could result in degenerative changes. Methods. The forelimbs of 30 rats were amputated when they were 1-month old. These rats were kept in the custom-made cages and were forced to stand upright on their hind-limbs and tails to obtain water and food. Normal rats of the same ages kept in regular cages were used as control. The rats were killed at 5, 7, and 9 months after the surgery, and the intervertebral discs samples of lumbar spine were harvested for histologic and immunohistochemical studies. Total RNA isolated from these samples was used for real-time PCR of type II collagen (Col2 alpha 1), type X collagen (Col10 alpha 1), matrix metalloproteinase-13 (MMP-13), aggrecan, and disintegrin and metalloproteinase with thrombospondin motifs 5 (ADAMTS-5). Results. Histologic analysis showed degenerative changes of the intervertebral discs after surgery such as disordered collagen structure of endplate cartilage, fragmentation of annulus fibrosus, and decreased height of disc. Immunostaining revealed decreased protein level of type II collagen and increased protein expression of type X collagen. Real-time PCR showed upregulated expression of MMP 13, ADAMTS-5, and Col10 alpha 1 mRNA and downregulated mRNA expression of Col2 alpha 1 and aggrecan. Conclusion. Long-term and repeated assumption of the upright stance accelerates disc degeneration in rats.