Effects of shear force on intervertebral disc: an in vivo rabbit study

Purpose A new in vivo rabbit model was developed to investigate the effects of shear force on intervertebral disc (IVD). Methods Japanese white rabbits ( n = 38) were used for this study. The L4/5 discs in Group A ( n = 10) were subjected to a constant shear force (50 N) using a custom-made external loading device for 1 month; in Group B ( n = 10) for 2 months; whereas in Group C ( n = 10), loading device was attached to the spine but the discs remained unloaded. Group D ( n = 8) was a non-operated intact control group. After loading, the loading devices were taken out and the animals were given X-ray and MRI examination. After X-ray and MRI examination, the animals were euthanized for histological analysis. Results After 1 and 2 months of loading, radiographic findings showed significant disc height narrowing in L4/5 discs of the animals in loading groups, and slight lumbar spondylolisthesis in some animals of Group B. MRI showed a significant decrease in nucleus pulposus (NP) area and signal intensity from T2-weighted images. Histologically, loss of normal NP cells and disorganization of the architecture of the annulus occurred, and proteoglycan stain decreased. Conclusions The results of this study suggest that disc degeneration can be induced by hyper-physiological shear loading in the rabbit IVD. Long-term shear loading may result in structural disc failure inducing lumbar spondylolisthesis and progressive disc degeneration, which, however, has to be proven by further studies.