ABSTRACT
Growth factors are important regulators of the intervertebral disc extracellular matrix and are involved in inducing the neovascularization process that accompanies disc degeneration (DD) and disc herniation (DH). In DH, newly formed blood vessels (1) contribute to resorption of the extruded disc tissue, which is variously composed of nucleus pulposus, annulus fibrosus, or endplate (2). Of clinical interest is the fact that of these tissues that may all or in various combinations form the herniated tissue, nucleus pulposus is the most leukotactic (3). In several studies (4,5), macrophages have been demonstrated in extruded disc tissue (Figs. 1, 2) to be instrumental in mediating tissue resorption and phagocytosis. Macrophages gain access to pathological disc tissue (DD or DH) by way of newly formed blood vessels (Fig. 3). Thus growth factors are also, at least indirectly, involved in the resorption process. At the moment, it is not yet known whether they may also have a more direct role. Of the growth factors we have screened, only one, namely transforming growth factor-beta (TGF-b), is present in normal disc (6,7). When the disc degenerates, and finally herniates, either into the nerve root canal or the spinal canal, an increasing number of growth factors become activated, creating a cascade that regulates tissue remodeling and neovascularization.
