Effects of basic fibroblast growth factor on spontaneous resorption of herniated intervertebral discs - An experimental study in the rabbit

Study Design. Histologic examination was performed on the autologous interv ertebral disc material that was removed from the intervertebral space at L1 -L2 and then relocated to the L4 posterior epidural space after the additio n of basic fibroblast growth factor (bFGF) in a rabbit. Objectives. To evaluate whether basic fibroblast growth factor influences t he resorption process of the herniated intervertebral disc through the prom otion of angiogenesis and chemotaxis. Summary of Background Data. It has been reported that newly formed vessels, inflammatory cells, and their products may play an important role in the s pontaneous resorption process of herniated intervertebral discs. In a rabbi t model that mimics the sequestration type of intervertebral disc herniatio n, it has been reported that the autologous intervertebral disc material th at relocated into the epidural space was penetrated by newly formed vessels originating from the epidural fat tissue. Therefore, it is possible that p romotion of angiogenesis may influence the resorption of herniated interver tebral discs. Basic fibroblast growth factor is well known as an angiogenes is stimulation factor in vivo. Methods. Thirty-six adult rabbits were divided into three groups. The L1-L2 intervertebral disc was partially incised through a retroperitoneal approa ch in each rabbit. The harvested disc material, which contained nucleus pul posus and anulus fibrosus, was immersed in one of three kinds of solution b efore relocation into the posterior epidural space at L4. In the control gr oup, the harvested intervertebral disc was immersed in physiologic saline f or 2 hours before relocation. In the group receiving 5 mu g bFGF, the disc was immersed in 5 mu g/mL bFGF for 2 hours before the relocation. In the gr oup receiving 20 mu g bFGF, the disc was immersed in 20 mu g/mL bFGF for 2 hours before the relocation. Rabbits of each group were killed for histolog ic examination 1, 2, 4, and 8 weeks after surgery. Results. In the bFGF-treated groups, newly formed vessels were observed to be in more numerous than those in the control group, 1 and 2 weeks after su rgery. The number of inflammatory cells, including macrophages, lymphocytes , and fibroblasts, also increased in the bFGF-treated groups. the period fr om the surgery to the degradation of the intervertebral disc in the bFGF-tr eated groups was shorter than that in the control group, although the resor ption process of the relocated discs was also observed in the control group . The size of relocated intervertebral discs in the bFGF-treated groups dec reased at a higher rate than in the control group as time progressed. The r ate of decrease in the size of discs in the group treated with 20 mu g bFGF was more than that in the group treated with 5 mu g. Conclusions. Epidural injection of bFGF facilitated the resorption of the i ntervertebral disc relocated to the epidural space.