Fresh frozen intervertebral disc allografting in a bipedal animal model

Study Design. An in vivo experimental study to examine the possibility of using fresh frozen intervertebral disc allograft in disc transplantation. Objectives. To investigate the long-term radiographic, pathologic, biochemical, and biomechanical changes of fresh frozen disc allograft in a bipedal animal model. Summary of Background Data. It has been shown that intervertebral disc autograft is able to survive and maintain some degree of tissue metabolism and segmental mobility after transplantation in a bipedal animal model. However, the long-term results of disc allografting and the associated problems of graft rejection are unknown. Methods. Seventeen rhesus monkeys (15 male, 2 female) between 5 and 8 years of age and weighing between 6.7 and 11.8 kg were used in this study. Of these 17 subjects, two were used as intervertebral disc donors and three were used as controls for the biomechanical testing. The remaining 12 monkeys were randomly divided into a short-term group (n = 4, followed up for 2, 4, 6, and 8 weeks, respectively), a midterm group (n = 6, 6 months), and a long-term group (n = 2, 24 months). Radiologic, histologic, biochemical, and biomechanical changes were investigated. Results. Radiography and macro- and microhistologic examination showed severe disc degeneration at 24 months of follow-up. Disc height decreased mainly in the early postoperative stage. Decreased water, proteoglycan, and hydroxyproline contents of the allograft were observed at 6 and 24 months of follow-up. The biomechanical properties of the transplanted allograft were similar to those of control. Conclusion. Fresh frozen disc allografts can survive and maintain some degree of cell metabolism and segmental mobility at 24 months after transplantation. However, severe disc degeneration is also observed at this stage.