Effects of hepatocyte growth factor and platelet-derived growth factor on the repair of meniscal defects in vitro.

Injuries to the avascular region of the meniscus occur frequently and may be difficult to repair. This study was designed to determine whether growth factors could diffuse from a collagen sponge or a collagen gel into meniscal tissue and stimulate healing of defects using an in vitro model. The diffusion of platelet-derived growth factor (PDGF) from the collagen carriers into the medium was rapid with approximately 50% being released from the collagen sponge within the first hour. After 5 d of incubation, 8% of the PDGF was present in the meniscus, 11% in the collagen sponge, and 62% had been released into the medium. Similar results were obtained when a collagen gel was used as a carrier. Histological evaluation of the meniscal explants after 2 wk in culture revealed extensive proteoglycan staining in the areas surrounding defects treated with either hepatocyte growth factor (HGF) or PDGF compared with controls without growth factor. The HGF-PDGF treatment resulted in alignment and migration of meniscal cells toward the defect, which was not observed in untreated controls. At 3-7 d, increased number of cells were observed in defects treated with collagen gels (but not the sponge) with PDGF-HGF. At 4 wk, combined HGF-PDGF treatment resulted in the formation of tissue with birefringence by polarized microscopy, suggestive of organized collagen. The data suggest that use of specific PDGF-HGF may enhance the repair of meniscal injuries.