Tissue engineering of cartilage: the road a group of researchers have traveled

Articular cartilage is composed of chondrocytes and matrix, and it is diffi cult for cartilage to heal after injury. In 1743, Hunter had stated that, “cartilage once destroyed is never recovered.” This was true until 2003, when Koshino and colleagues reported regeneration of degenerated articular cartilage after high tibial valgus osteotomy for medial compartmental osteoarthritis of the knee. In their report, 47 (32.2%) of 146 knees were totally covered by new regenerated fi brocartilage or hyaline cartilage. Histology also demonstrated hyaline cartilage regeneration on previously degenerated medial femoral condyle. However, the regeneration occurred in only one-third of the knees. Many other treatments have also been used directly on focal lesions of the articular cartilage of the knee, including abrasion arthroplasty, microfracture, autogenous chondrocyte implantation, allogenous osteochondral transplantation, and autogenous osteochondral transplantation (“mosaicplasty”). Johson reported a 77% success rate at a 2-year follow-up for abrasion arthroplasty, although the 5-year follow-up success rate decreased to 51%–53%. The disadvantage of this technique is that abrasion may produce thermal necrosis. In contrast, Steadman et al. used a microfracture technique that increased the stiffness of the bone and produced no heat necrosis, thus preserving the subchondral bone plate. After penetration of the bone plate, continuous passive motion was used for 6–8 weeks with limited weight bearing. This yielded a 75% success rate after 7 years of follow-up. Autogenous chondrocyte implantation (ACI) was reported in 1994. At a 2-year follow-up, 87% good to excellent results were reported in femoral lesions, but patellar lesions tended to have a worse outcome. Peterson et al. reported that at 2–9 years of follow-up good results were obtained in 92% of isolated femoral condyle lesions, 65% of patellar lesions, and 67% of multifocal chondral damage using ACI. The disadvantages of ACI include loss of phenotype in monolayer culture and leakage of cell suspension when injecting it into focal lesions that had been covered by periosteum during the repair procedures. Uneven distribution of cells is another shortcoming. Allogenous osteochondral transplantation has been used, especially for sports injury, and 60%–88% good/ excellent results have been reported at 4.5–7.8 years of follow-up. Transmission of diseases and immune rejection are pitfalls of the technique. Autogenous osteochondral transplantation was used by Hangody et al. to treat focal osteochondral defects. Among 57 patients, 91% good to excellent results were noted after 3 years of follow-up. The disadvantage of this technique is poor integration of cartilage between the recipient site and chondral graft and hypertrophy of the chondral graft, which resulted in an irregular joint surface. Based on these previous disadvantages, tissue engineering of cartilage emerged, and biotechnology of stem cells and scaffolds has progressed rapidly in recent years.