Histomorphological investigation of microfracture localization in rabbit osteochondral defect model

Introduction: Joint cartilage, is a tissue with poor blood supply and healing potential. Microfracture is the most commonly applied method of treatment in cartilage defects of the knee. In microfracture surgery, the holes are randomly drilled into the subchondral bone. The location of the holes relative to the defect site and its effect on cartilage healing is still unknown. In this study, we aimed to investigate the effect of different fracture localizations on cartilage healing, in the rabbit knee osteochondral defect model from a histomorphological perspective Methods: In this study, 29 adult New Zealand rabbits were divided into 5 groups. Cartilage defects with a diameter of 5 mm and a depth of 3 mm were created in the patellar groove of 24 rabbits. In Group 1 (defect control) only the defect was created (n = 6). In Group 2 (peripheral single), 1 microfracture was performed at 12 o'clock of the defect (n = 6). In Group 3 (central), a micro-fracture procedure was performed at the central of the defect (n = 6). In group 4 (peripheral double), one fracture was performed at 12 and 6 o'clock of the defect (n = 6). Five rabbits with no defects and no surgery were divided into Group 5 (healthy control) group (n = 5). The animals were sacrificed after 8 weeks; cartilage healing was evaluated by macroscopic, histological, immunohistochemical and SEM analysis. Results: In the peripheral couple (Group 4) group, better cartilage healing was observed in all parameters (macroscopic, histological and immunohistochemical parameters) compared to the other groups (P <0.05). While %79 of the defect area was filled with repair tissue in the peripheral double (group 4) group; 73% of the defect area in the peripheral single (Group 2) group, 56% of the defect area in the central (Group 3) group and 45% of the defect area of control (Group 1) group was filled with repair tissue, respectively. The ICRS score (macroscopic cartilage healing assessment) was significantly higher in the peripheral single (Group 2) group compared to the central (Group 3) and the control (Group 1) group. Type Ⅱ Collagen and Aggregate immunoreactivity were significantly stronger in the central group (Group 3) than the peripheral single (group 2) and control (Group 1) group (P <0.05). Conclusion: In this study, we found that the microfracture performed at the peripheral margin of the defect was better at filling the defect site. This study proved, that the interaction of the pluripotent cells, released from the microfracture site, with the intact cartilage significantly enhanced the quality of the repair tissue.