[Experimental study on cryopreservation and intramuscular allografting of vertebral body and disc units].

This study investigated optimal conditions for preservation and intramuscular allografting of vertebral body and disc units. First, thirty-one vertebral body and disc units were removed from rabbits and divided into three groups: a slow freezing group, a quick freezing group, and a fresh non-freezing group. In the slow freezing group, disc units were slowly cryopreserved by decreasing temperatures from 4 to -80 degrees C using a program freezer. In the quick freezing group, they were rapidly cryopreserved by freezing to -80 degrees C without a program freezer. Second, to determine favorable duration of immersion in cryoprotectant (10% dimethyl sulfoxide), another 20 vertebral body and disc units were divided into four groups: immersed at 4 degrees C for 30, 90, 240 and 1440 minutes. After immersion, they were cryopreserved slowly using a program freezer. These disc units were thawed and examined histologically and biochemically. In the slow freezing group, both cell number in the anulus fibrosus and the value of 35SO4 incorporation in the disc were higher than those in the quick freezing group, and the disc viability of the 90-minute group was the highest. On the basis of these experiments, vertebral body and disc units were grafted into the back muscles of rabbits. To investigate the viability of the disc after allografting, another 38 specimens were grafted into the back muscles and examined after 4 or 12 weeks. The values for 35SO4 incorporation of each group at 4 weeks were about 80% of the pre-grafting level and those at 12 weeks were about 60%, and the viability of discs maintained. There were no significant differences between the slow freezing group, the quick freezing group, and the fresh non-freezing group after grafting. Further study is needed to determine a method in maintaining viability of the disc after grafting.