Transplantation of cryopreserved osteochondral dowel allografts for repairof focal articular defects in an ovine model

The purpose of this study was to test whether successful cryopreservation o f osteochondral tissue is possible and whether, with the appropriate surgic al procedure, it can be used for the successful repair of focal articular d efects within joints. Fresh (nonfrozen) and snap-frozen (plunged in liquid nitrogen and thawed in a water bath at 37 degrees C, repeated three times) autografts were used as positive and negative controls, respectively. Snap- frozen, frozen (fresh tissue placed in a freezer at -80 degrees C), and cry opreserved (immersed in 10% dimethyl sulfoxide for 30 minutes and then froz en at 1 degrees C/min to -80 degrees C) allografts were transplanted into t he knees of adult sheep. Outcomes were evaluated 3, 6, and 12 months after transplantation. The morphological, histological, biochemical, and biomecha nical behaviors and characteristics of the graft cartilage, the host cartil age adjacent to the grafts, and the opposing tibial cartilage were assessed . Freezing protocols that yielded poor chondrocyte recovery after thawing ( frozen and snap-frozen) resulted in poor overall graft outcome. The cryopre servation protocol, however, resulted in intermediate recovery (50%) of cho ndrocytes and in intermediate overall graft outcome compared with fresh aut ografts. The membrane integrity of the allograft chondrocytes immediately f ollowing cryopreservation was identified as the most reliable predictor of long-term outcome of the graft. Further improvements in cryopreservation te chnique may lead to an effective method of banking osteochondral tissue for successful transplantation for the repair of focal defects and larger join t reconstructions.