The effect of compressive force applied to the intervertebral disc in vivo. A study of proteoglycans and collagen.

STUDY DESIGN

Coil springs were stretched and attached to produce a compressive force across the lumbar intervertebral discs of dogs for up to 27 weeks.

OBJECTIVE

To test the hypothesis that a high compressive force applied over a period of time affects the production of proteoglycans and collagen by the intervertebral disc cells.

SUMMARY OF BACKGROUND DATA

It is a commonly held belief that high forces applied to the intervertebral disc, and to joints in general, play a role in causing degeneration.

METHODS

Pairs of stainless steel coil springs were stretched and attached to produce a compressive force across the lumbar intervertebral discs (L1-L2 and L3-L4) of 16 dogs. Dogs were killed between 13 and 27 weeks after the springs were attached. The discs (L1-L2 and L3-L4) were excised and assessed using immunohistochemical analyses and enzyme-linked immunosorbent assay; T13-L1 and L4-L5 were used as controls.

RESULTS

The main result relates to a group effect in the six dogs, assessed using enzyme-linked immunosorbent assay, that were generally at the highest values of force for the greatest number of weeks. For the nucleus, but not the anulus, Spearman rank correlations revealed a strong correlation between increases in force and force-weeks (force multiplied by number of weeks) and increases in collagen type I accompanied by decreases in proteoglycans, chondroitin sulfate, and collagen type II for both experimental discs (L1-L2 and L3-L4), as compared with corresponding values in the controls (T13-L1 and L4-L5). In other words, as either the force or the force-weeks increased, the effect on the nucleus became greater.

CONCLUSION

A high compressive force applied to the disc over a period of time initiates changes in proteoglycans and collagen.