Role of Mesenchymal Stem Cells Densities When Injected as Suspension in Joints with Osteochondral Defects.

OBJECTIVE: The aim of this study was to evaluate an intraarticular injection of different doses of autologous mesenchymal stem cells (MSCs) for improving repair of midterm osteochondral defect. DESIGN: At 4 weeks postoperative marrow stimulation model bilaterally (3 mm diameter; 4 mm depth) in the medial femoral condyle, autologous MSCs were injected into knee joint. Twenty-four Japanese rabbits aged 6 months were divided randomly into 4 groups ( n = 6 per group): the control group and and MSC groups including 0.125, 1.25, and 6.25 million MSCs. Repaired tissue was assessed macroscopically and histologically at 4 and 12 weeks after intraarticular injection of MSCs. RESULTS: At 12 weeks, there was no repair tissue in the control group. The gross appearance of the 1.25 and 6.25 million MSC groups revealed complete repair of the defect with white to pink tissue at 12 weeks. An osteochondral repair was histologically significantly better in the 1.25 and 6.25 million MSC groups than in the control and 0.125 million MSC groups at 4 and 12 weeks, due to presence of hyaline-like tissue in the deep layer at 4 weeks, and at 12 weeks hyaline cartilage formation at the periphery and fibrous tissue containing some chondrocytes in the deep layer of the center of the defect. Subchondral bone was restructured in the 1.25 and 6.25 million MSC groups, although it did not resemble the normal bone. CONCLUSION: An intraarticular injection of 1.25 or 6.25 million MSCs could promote the repair of subchondral bone, even in the case of midterm osteochondral defect.

Cell Magnetic Targeting System for Repair of Severe Chronic Osteochondral Defect in a Rabbit Model.

The aim of this study was to investigate a cell delivery system for repair of severe chronic osteochondral defects using magnetically labeled mesenchymal stem cells (m-MSCs), with the aid of an external magnetic device, through the accumulation of a small number of m-MSCs into a desired area and to detect the suitable number of autologous m-MSCs needed for repair of the defect. Twenty-six male Japanese white rabbits aged 6 months were used. An osteochondral defect was created bilaterally at the weight-bearing surface of the medial femoral condyle of the rabbits' knees (3 mm diameter; 4 mm depth). At 4 weeks after creation of the defect, autogenic transplantation of the m-MSCs into the defect area was performed, followed by 10-min exposure to an external magnetic device, where animals were divided into four groups: high (1 × 10(6) m-MSCs), medium (2 × 10(5) m-MSCs), low (4 × 10(4) m-MSCs), and control (PBS injection). At 4 and 12 weeks posttransplantation of m-MSCs, repaired tissue was assessed histologically using the Fortier score with toluidine blue staining. Transplantation of a low number of m-MSCs was not enough to improve osteogenesis and chondrogenesis, but the medium and high groups improved repair of the chronic defect with chondrogenic tissues and showed histologically significantly better results than the control and low groups. The use of a magnetic targeting system for delivering m-MSCs has the potential to overcome the clinical hurdles for repair of the severe chronic osteochondral defect. Furthermore, this system is predicted to produce good clinical outcomes for humans, not only to repair osteochondral defects but also to repair a variety of damaged tissues.