Autogenous Osteochondral Transplantation Mosaicplasty (An Animal Study on Sheep)

Background: Autogenous osteochondral grafting of articular defect in weight-bearing surface of large joints has proven to be a proper biomechanical and physiological solution for localized full-thickness defects.Objective: To study the gross and histopathological results of mosaicplasty in an animal model (sheep’s medial femoral condyle), evaluating the factors of defect and graft size, assessing the effect of fixation with only cancellous bone impaction between graft columns, and early free post-operative motion.Methods: Fourteen medium sized sheep were the subject of the study. Cylindrical osteochondral grafts of 4 mm and 6 mm diameter and 1 cm length from the periphery of the medial femoral condyles at the patellofemoral joint were used to fill corresponding 8 mm and 15 mm diameter cylindrical defects of 1 cm depth at the weight-bearing surface of medial femoral condyles.  The spaces between the grafts were packed with cancellous bone with double gloved thumb. The sheep were free for activities and weight bearing after the operation. Two of the 14 sheep died.  The first due to sepsis and the other of cardiorespiratory arrest during anesthesia induction.  All sheep were sacrificed after 4 months and their knees collected as specimens for further gross and histopathological studies.Results: All grafted defects except one healed with smooth cartilage. The quality of cartilage was evaluated by   histopathological criteria, rating the cellular morphology, surface regularity as well as structural integrity and thickness of cartilage, binding to adjacent normal cartilage and clustering.  Twenty-three out of 24 specimen showed excellent or good result, that is a success rate of 95.8%.Conclusion: Mosaicplasty, autogenous osteochondral grafting in this animal study was effective and successful even in larger defects of 15 mm diameter. Cancellous bone cementing between the cylindrical grafts, respecting the normal convexity of the femoral condyle insertion of obliquely harvested grafts at the periphery of the defects and freedom of motion and activity were all helpful in obtaining good results 4 months after graft implantation.