IntroductionChemonucleolysis with chymopapain, which was first clinically used by Smith [12], is an effective treatment for intervertebral disc herniation. However, anaphylactic reactions, in particular, have limited the use of this treatment. To prevent anaphylactic reactions, skin testing and the use of H1 and H2 blocking agents have been recommended. Anaphylactic reactions to chymopapain have decreased in frequency over the years [5]. However, the risk of anaphylaxis still remains. Accordingly, an alternative substance for chemonucleolysis has been sought.Proteoglycans are major structural components of the intervertebral disc, and their concentration and organization in the extracellular matrix have a considerable influence on its mechanical properties. Bayliss et al. [2] described a reduction in proteoglycan synthesis rates when disc hydration was decreased.Shioda [11] suggested a mechanism for a decrease in the intradiscal pressure after hypertonic saline injection, by which partial cell necrosis leads to a decrease in matrix production. Released lysosomal enzymes from the cells could then cause partial proteolysis. As a result, the amount of proteoglycan decreases, which means the water-binding capacity decreases. He suggested that the direct effect of hypertonic saline on the matrix was minimal.We have previously reported intradiscal pressure after intradiscal injection of hypertonic saline in rabbits, but the results of the study found that hypertonic saline injected Abstract Chemonucleolysis with chymopapain is an effective alternative to an operation for the treatment of some patients who have a lumbar intervertebral disc herniation. However, chymopapain is associated with rare but serious complications. Accordingly, alternative substances for chemonucleolysis have been sought. The main beneficial effect of chemonucleolysis derives from the decrease in the intradiscal pressure. We have previously reported that hypertonic saline injected into the intervertebral discs decreased the intradiscal pressure, but only temporarily. The present experimental study investigated changes in the intradiscal pressure after a repeat intradiscal injection of hypertonic saline. The lumbar intervertebral discs of 18 living rabbits were examined: 10% hypertonic saline was injected intradiscally just once in 12 rabbits, and the same dosage was injected again, 4 weeks later, in the same animals. The intradiscal pressure was measured at 1, 4, 8, and 12 weeks after the second injection. The remaining six rabbits were used as controls, without puncture and without injection. The intradiscal pressure of the group with repeat hypertonic saline injection at 4 weeks was significantly lower than that of the control group. The decreased pressure showed a tendency to increase at 8 weeks, and it had recovered at 12 weeks. The results of this study suggest that repeat hypertonic saline injections may be clinically useful.
Although chemonucleolysis with chymopapain is a long-established treatment for lumbar intervertebral disc herniation, serious complications have been reported. Accordingly, alternative substances for chemonucleolysis have been sought. The main beneficial effect of chemonucleolysis derives from the decrease in intradiscal pressure. Several previous studies have investigated the relationship between physiological saline injection and disc mechanics in cadaveric specimens [2, 5, 16]. However, no previous study has assessed the intradiscal pressure after intradiscal injection of "hypertonic saline" in living animals. The present study compared the changes in intradiscal pressure after intradiscal injection of hypertonic saline with those after chymopapain injection. The lumbar intervertebral discs of 26 living rabbits were examined: 10% hypertonic saline was injected in ten rabbits, and chymopapain (10 pikokatal units) was injected intradiscally in another ten, with the remaining six being used as controls. The intradiscal pressure was measured at 1, 4, and 12 weeks after injection. The intradiscal pressure of the hypertonic saline-injected group at 4 weeks was significantly lower than that of the control group, but by 12 weeks it had recovered. On the other hand, that of the chymopapain-injected group remained significantly lower than that of the control group at 12 weeks. The results of this study found that hypertonic saline injected into the intervertebral discs temporarily decreased the intradiscal pressure.
Summary: To study the effect of laser irradiation on normal lumbar discs, a 2100 nm Holmium (HO)-YAG laser irradiation was applied to the 83 lumbar discs of 23 adult rabbits. The extent of disc vaporization, the temperature changes in the surrounding tissues, and changes in the radiograph and MRI findings were assessed after laser irradiation. When laser irradiation was delivered to the discs, the disc weight decreased linearly with the increase in total laser energy, indicating steady vaporization of disc material. The temperature was highest at the site of the guide needle. Laser irradiation was delivered at 0.5 J/pulse or 1.4 Jlpulse X5 pulses/sec to the intervertebral discs, and radiographs and T2-weighted MRI of the irradiated discs were investigated at 1, 4, and at 12 weeks after irradiation. At 1 week after irradiation at 0.5 and 1.4 J/pulse, the radiographs showed a decrease in the disc height. At 12 weeks after irradiation at 0.5 J/pulse, the disc height had restored to normal, while the decrease was persistent after irradiation at 1.4 Jlpulse. At 1 week after irradiation, MRI showed a decrease in the signal intensity of discs treated at 0.5 Jlpulse, but the decrease was recovered at 12 weeks. After irradiation at 1.4 Jlpulse, the decrease in signal intensity was also recovered by 12 weeks, but the recovery was less than the recovery after treatment at 0.5 J/pulse. Laser irradiation is applicable for the treatment of intervertebral discs, but it is necessary to select the optimal operating conditions. It may also be necessary to change the power of irradiation according to the pathological condition of the disc being treated.
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