[A biochemical analysis of experimental chemonucleolysis].

We have studied the mechanical properties of enzyme-injected canine intervertebral discs by quasi-static compression tests, dynamic vibration tests and histology at 2 weeks (short-period group) and within 6 months (long-period group) after enzyme injection. The findings of each group were compared with those of normal discs as a control. The results were as follows; The quasi-static tests: In the short-period group, normalized stiffness of the discs was reduced significantly and the normalized creep rate was increased. The intradiscal pressures produced by external loading in short-period discs were almost half those of the control. In the long-period group such values tended to recover partially. The dynamic tests: In the short-period group, both elasticity and viscosity were reduced, while in the long-period group elasticity recovered but viscosity did not. These findings suggest that the shock-absorbing ability of enzyme-injected discs does not recover.