THE EFFECT OF RECOMBINANT HUMAN BONE MORPHOGENETIC PROTEIN-2 (RHBMP-2) ON THE HEALING OF FULL-THICKNESS DEFECTS OF ARTICULAR-CARTILAGE

Articular cartilage has a limited capacity for repair, We investigated the effect of rhBMP-2 (recombinant human bone morphogenetic protein-2 ) on the healing of full-thickness osteochondral defects in adult New Zealand White rabbits, A single defect, three millimeters wide by thre e millimeters deep,was created in the trochlear groove of the right fe mur in eighty-nine rabbits, The defect was either left empty filled wi th a plain collagen sponge, or filled with a collagen sponge impregnat ed with five micrograms of rhBMP-2. The animals were killed at four, e ight, or twenty-four weeks, and the repair tissue was examined histolo gically and evaluated with use of a grading scale, The defects also we re examined immunohistochemically for the presence of type-II collagen at four and eight weeks, The rate of bone repair was evaluated with f luorescent labeling of bone at two and four weeks and with use of fluo rescence microscopy at eight weeks, Treatment with rhBMP-2 greatly acc elerated the formation of new subchondral bone and improved the histol ogical appearance of the overlying articular surface, At twenty-four w eeks, the thickness of the repair cartilage was 70 per cent that of th e normal adjacent cartilage and a new tidemark usually had formed betw een the repair cartilage and the underlying subchondral bone. The aver age total scores on the histological grading scale were significantly better (p < 0.01) for the defects treated with rhBMP-2 than for the un treated defects (those left empty or filled with a plain collagen spon ge) at all time-points, Immunostaining with an antibody against type-I I collagen showed the diffuse presence of this cartilage-specific coll agen throughout the repair cartilage in the treated defects, The untre ated defects demonstrated minimum staining with this antibody, CLINICA L RELEVANCE: The operative removal of cartilage damaged as a result of trauma or focal osteoarthrosis is of little value because of the limi ted capability of articular cartilage to repair, If the damaged cartil age were to be removed and the tissue were induced to heal, the self-p erpetuating process of osteoarthrosis might be prevented, We describe the capacity of rhBMP-2 to accelerate the healing of full-thickness de fects of articular cartilage and to improve the histological appearanc e and biochemical characteristics of the repair cartilage, These impro vements were evident as long as twenty-four weeks postoperatively in a dult rabbits, Because of the technical simplicity of delivering a reco mbinant protein growth factor compared with transplanting cells, and b ecause of the improvement in healing afforded by rhBMP-2, the use of t his growth factor and related proteins to influence the healing of def ects of articular cartilage should be investigated further.