Internal intervertebral disc mechanics as revealed by stress profilometry.

A technique was developed for measuring the distribution of stress within loaded cadaveric intervertebral discs. A strain-gauged membrane mounted on the side of a 1.3-mm diameter needle was pulled through the disc at constant speed. The orientation of the membrane was changed by rotating the needle, so that profiles of vertical and horizontal components of compressive stress could be obtained. The measurements were reproducible and did not perturb the tissue to any significant extent. Stress profiles varied considerably between discs and were highly dependent on the severity of degenerative changes. They also showed that the mechanical behavior of individual disc tissues was dependent not only on their location, but also on the loading and loading history of the disc. The new insight into internal disc mechanics revealed by stress profilometry may lead to a greater understanding of the mechanisms of disc function and failure.