Use of a Biphasic Graft Constructed with Chondrocytes Overlying a β-Tricalcium Phosphate Block in the Treatment of Rabbit Osteochondral Defects

To evaluate the ability of a biphasic construct to repair osteochondral defects in articular cartilage, plugs made of chondrocytes in collagen gel overlying a resorbable porous β-tricalcium phosphate (TCP) block were implanted into defects in rabbit knees. The repair tissue was evaluated at 8, 12, and 30 weeks. Eight weeks after implantation of the biphasic construct, histologic examination showed hyaline-like cartilage formation that was positive for safranin O and type II collagen. At 12 weeks, most of the β-TCP was replaced by bone, with a small amount remaining in the underlying cartilage. In the cell-seeded layer, the newly formed middle and deep cartilage adjacent to the subchondral bone stained with safranin O, but no staining was observed in the superficial layer. In addition, cell morphology was distinctly different from the deep levels of the reparative cartilage, with hypertrophic cells at the bottom of the cartilaginous layer. At 30 weeks, β-TCP had completely resorbed and a tidemark was observed in some areas. In contrast, controls (defects filled with a β- TCP block alone) showed no cartilage formation but instead had subchondral bone formation. These findings indicate that β-TCP-supported chondrocytes in collagen gel can partially repair isolated articular cartilage osteochondral defects.