Abstract
Clinically, a large number of patients have persistent low back pain attributable to intervertebral disc (IVD) degeneration. After the concept of biologically regenerating the degenerated IVD using growth factor injection was first proposed in early 1990, the advancement of molecular technology to produce recombinant proteins, including growth factors, on an industrial scale accelerated research in this field. The purpose of this review is to summarize the most recent findings of the in vitro and in vivo effects of growth factors on the IVD and, further, to discuss the limitations of growth factor therapy and its clinical implications. In vitro data showed that stimulation of matrix synthesis by growth factors alters the balance of homeostasis by shifting cellular metabolism to the anabolic state. In vivo data using small animals has shown the possibility of using growth factors as a "structural modifying therapy". Based on in vitro and in vivo data previously reported, the clinical application of growth factors by direct injection of protein into the nucleus pulposus or anulus fibrosus was shown to be feasible as a new therapeutic intervention for treatment of disc degeneration. Stimulation of the biological repair process will create a new category of therapy to treat disc degeneration, where no active treatment currently exists, between conservative therapies and more aggressive therapies such as fusion or disc replacement. However, it should be noted that there are several important factors to be taken into consideration. In a relatively advanced degenerative condition, the supply of nutrients is disturbed and stimulation of cellular activity by growth factors may result in an increased demand for nutrients, eventually inducing an adverse event. Further investigations of the optimal environment for growth factor stimulation should be pursued. Growth factor therapy, which has experimental evidence supporting it to be a "structural modifying therapy", may not be a "symptom modifying therapy" that is able to resolve the symptoms associated with pathologic changes. Therefore, further studies on the effect of growth factor therapy on pain are essential to shed light on its therapeutic usefulness for degenerative disc disease.