CRYOPRESERVATION OF ARTICULAR-CARTILAGE - ULTRASTRUCTURE OBSERVATIONSAND LONG-TERM RESULTS OF EXPERIMENTAL DISTAL FEMORAL TRANSPLANTATION

Ultrastructural changes associated with the freeze-preservation of hum an articular cartilage have been investigated and related to changes i n transplanted distal femoral allografts in nonhuman primates. Human o steoarticular specimens were frozen at 2 degrees/minute in the presenc e of 15% glycerol and kept in liquid nitrogen freezers (vapor phase) f rom one day to two gears. Ultrastructural changes were confined primar ily to chondrocytes and were related to the freezing phenomenon, not t o the time of storage. The cartilage matrix was affected little, expla ining why articular cartilage initially survives clinical transplantat ion, but later undergoes degenerative changes. Osteoarticular allograf ts of baboons were frozen in an identical fashion to the human articul ar cartilage and transplanted into adult baboons. Long-term observatio ns (five years) on these animals showed healing and replacement of the osseous portion of cryopreserved allografts. Fractures that appeared to coincide with maximum revascularization of the graft were the princ ipal complication. Articular surfaces of the cryopreserved allografts underwent degenerative changes over five years. These degenerative cha nges were also manifested radiologically and appeared similar to those observed in humans. By contrast, fresh osteoarticular allografts heal ed poorly through fibrous union. However, in one of two fresh allograf ts, the articular cartilage remained intact five years after transplan tation.