Tissue-engineered composites for the repair of large osteochondral defects

Objective. To test the hypothesis that engineered cartilage can provide a mechanically functional template capable of undergoing orderly remodeling during the repair of large osteochondral defects in adult rabbits, as assessed by quantitative structural and functional methods. Methods. Engineered cartilage generated in vitro from chondrocytes cultured on a biodegradable scaffold was sutured to a subchondral support and the resulting composite press-fitted into a 7-mm long, 5-mm wide, 5-mm deep osteochondral defect in a rabbit knee joint. Defects left empty (group 1) or treated with cell-free composites (group 2) served as controls for defects treated with composites of engineered cartilage and the support, without or with adsorbed bone marrow (groups 3 and 4, respectively). Results. Engineered cartilage withstood physiologic loading and remodeled over 6 months into osteochondral tissue with characteristic architectural features and physiologic Young's moduli. Composites integrated well with host bone in 90% of cases but did not integrate well with host cartilage. Structurally, 6-month repairs in groups 3 and 4 were superior to those in group 2 with respect to histologic score, cartilage thickness, and thickness uniformity, but were inferior to those in unoperated control tissue. At 6 months, Young's moduli in groups 2, 3, and 4 (0.68, 0.80, and 0.79 MPa, respectively) approached that in unoperated control tissue (0.84 MPa), whereas the corresponding modulus in group 1 (0.37 MPa) was significantly lower. Conclusion. Composites of tissue-engineered cartilage and a subchondral support promote the orderly remodeling of large osteochondral defects in adult rabbits.