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

Abstract

Histologic examination was performed on the autologous intervertebral disc material that was removed from the intervertebral space at L1-L2 and then relocated to the L4 posterior epidural space after the addition of basic fibroblast growth factor (bFGF) in a rabbit. To evaluate whether basic fibroblast growth factor influences the resorption process of the herniated intervertebral disc through the promotion of angiogenesis and chemotaxis. It has been reported that newly formed vessels, inflammatory cells, and their products may play an important role in the spontaneous resorption process of herniated intervertebral discs. In a rabbit model that mimics the sequestration type of intervertebral disc herniation, it has been reported that the autologous intervertebral disc material that relocated into the epidural space was penetrated by newly formed vessels originating from the epidural fat tissue. Therefore, it is possible that promotion of angiogenesis may influence the resorption of herniated intervertebral discs. Basic fibroblast growth factor is well known as an angiogenesis stimulation factor in vivo. Thirty-six adult rabbits were divided into three groups. The L1-L2 intervertebral disc was partially incised through a retroperitoneal approach in each rabbit. The harvested disc material, which contained nucleus pulposus and anulus fibrosus, was immersed in one of three kinds of solution before relocation into the posterior epidural space at L4. In the control group, the harvested intervertebral disc was immersed in physiologic saline for 2 hours before relocation. In the group receiving 5 micrograms bFGF, the disc was immersed in 5 micrograms/mL bFGF for 2 hours before the relocation. In the group receiving 20 micrograms bFGF, the disc was immersed in 20 micrograms/mL bFGF for 2 hours before the relocation. Rabbits of each group were killed for histologic examination 1, 2, 4, and 8 weeks after surgery. 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 surgery. The number of inflammatory cells, including macrophages, lymphocytes, and fibroblasts, also increased in the bFGF-treated groups. The period from the surgery to the degradation of the intervertebral disc in the bFGF-treated groups was shorter than that in the control group, although the resorption process of the relocated discs was also observed in the control group. The size of relocated intervertebral discs in the bFGF-treated groups decreased at a higher rate than in the control group as time progressed. The rate of decrease in the size of discs in the group treated with 20 micrograms bFGF was more than that in the group treated with 5 micrograms. Epidural injection of bFGF facilitated the resorption of the intervertebral disc relocated to the epidural space.