Ingrowth of osteochondral grafts under the influence of growth factors: 6-month results of an animal study

Introduction: In the age of growth factors and gene therapy, the induction of cartilage healing remains an unsolved problem. Even in autologous grafting, one of the preferred methods of treatment for focal osteochondral lesions, chondral integration remains difficult. This study aims to define a possible positive influence of growth factor augmentation on the ingrowth of these transplants. Materials and methods: In an ovine model, questions regarding the healing of osteochondral transplants under the influence of two different growth factors were to be addressed. Two osteochondral autologous transplantations (OAT), one in the weight-bearing surface of each femoral condyle, were performed on the ovine knee using the standard operative protocol. One of the grafts was bathed in augmented PBS containing 50 μg bFGF or bone morphogenetic protein (BMP)-2 directly prior to implantation, while the other condyle served as the control. Two groups, consisting of eight sheep each, were evaluated for each growth factor after 6 months. Results: During the evaluation of all the specimens, neither osteophytes nor synovial changes were observed. The mechanical consistency of the cartilaginous tissue began to reach a level equivalent to the surrounding tissue at 6 months, independent of the use of growth factor. Macroscopically, the superficial border of the transplanted osteochondral plug could easily be outlined in all groups, while the cartilage interface of the bFGF specimens was determined to be less demarcated than the BMP augmented plugs or the controls. Radiographically, a solid osteointegration of the graft could be documented at 6 months in the native and augmented groups. In contrast, integration of the chondral surface of the OAT was not seen macro- or microscopically in any specimen, even though cartilage surfaces remained viable. A firm physical interdigitation of the reconstructed joint surface could not be demonstrated in either of the two augmented groups or the control population. The augmentation with bFGF and BMP-2 stimulated the osseous ingrowth and seems to expedite the remodelling process, but was not able to improve chondral healing. Conclusion: The lack of integration of the cartilaginous portion of the transplanted plugs into the reconstructed joint surface, even following the augmentation with bFGF and BMP-2, does not bode well for the long-term survival of the joint itself.