Study design: A retrospective, longitudinal study of 51 patients, covering a mean follow-up period of 81 months.
Objective: To observe the long-term temporal course of the height of human lumbar discs after chemonucleolysis. To document whether human lumbar discs reconstitute, thus characterizing the healing potential of central disc tissue.
Summary of background data: Although reconstitution of disc height within some months of chemonucleolysis has been observed in animal experiments, human lumbar discs have shown no tendency to regain their initial height within 1 year of treatment. To date, there has been no report on longer follow-up periods. The different reactions of animal and human discs may be dose-related or related to differences in tissue properties, physiologic environment or in vivo loading conditions.
Methods: Using a new protocol, the heights of lumbar discs were measured from sets of lateral radiographic views of 51 patients subject to chemonucleolysis by treatment with chymopapain (doses of 4000 or 3000 picokatals [pkat]). The sets comprised a view taken before treatment, a view taken (on average) 4 months after treatment, and a view taken (on average) 81 months after treatment. In the majority of patients, untreated discs adjacent to discs treated with chemonucleolysis served as control discs.
Results: Shortly after injection of chymopapain, all treated discs decreased in height. The height decrease of treated discs amounted to 15.8% on average. In the subcohort treated with 4000 pkat, the loss did not reverse during the entire follow-up period; in the subcohort treated with 3000 pkat a small fraction of the lost height was regained. Untreated neighboring control discs showed a minor (3.4%) decrease in height.
Conclusions: Human lumbar discs do not reconstitute after chemonucleolysis. Because the long-term temporal course of disc height in patients is in disagreement with observations from animal experiments, caution is suggested when generalizing results from animal studies to humans.