Effects of static compression with different loading magnitudes and durations on the intervertebral disc: An in vivo rat-tail study

Study Design. An in vivo rat-tail model was used to study the effects of static compression with different loading magnitudes and durations on the intervertebral disc. 

Objective. To investigate the effects of static compression with different loading magnitudes and durations on the intervertebral disc over a period of time. 

Summary of Background Data. A disc degeneration model is essential for studying therapeutic effects on degenerated disc. Static compression can induce degenerative-like changes in the intervertebral disc. However, the consequences of the simulation model over a period of resting have not been clearly documented, which may have confounding effects on the experimental outcome. 

Methods. Thirty-five rats were used. Static compressions with different loads (11 or 17 N) and durations (1 hour daily or continuous) were applied to the rat-tail caudal 8-9 disc for 2 weeks, and followed with 3 weeks of rest. The disc height was quantified in vivo on days 4, 18, and 39. The rats were killed and the discs were harvested for morphologic examination on day 39 after the disc height measurement. 

Results. Significant decrease in disc height was observed after continuous static compression for both 11 and 17 N, and continued during the resting period. The morphologic evaluation of the continuous compressed disc showed a decreased nuclear size, reduced number of nuclear cells, and irregular nuclear shape with inward bulging of disorganized annular collagen lamellas. Daily compression of 1 hour was found to induce a transient increase in disc height, but restored after the 3-week resting period. Favorable morphologic changes, including vacuolated nuclear cells and oval nuclear shape with well-organized annular collagen lamellas, were seen in the rat disc specimens with daily compression of 1 hour. 

Conclusion. Disc degenerative-like changes without recovery were demonstrated in the rat caudal disc after continuous compression. The changes in disc height and disc morphology were found to be dependent on the duration of load application and may have clinical implication. Copyright © 2008 Lippincott Williams & Wilkins, Inc.