Cryopreservation of articular cartilage. Ultrastructural observations and long-term results of experimental distal femoral transplantation.

Ultrastructural changes associated with the freeze-preservation of human articular cartilage have been investigated and related to changes in transplanted distal femoral allografts in nonhuman primates. Human osteoarticular specimens were frozen at 2 degrees/minute in the presence of 15% glycerol and kept in liquid nitrogen freezers (vapor phase) from one day to two years. Ultrastructural changes were confined primarily to chondrocytes and were related to the freezing phenomenon, not to the time of storage. The cartilage matrix was affected little, explaining why articular cartilage initially survives clinical transplantation, but later undergoes degenerative changes. Osteoarticular allografts of baboons were frozen in an identical fashion to the human articular cartilage and transplanted into adult baboons. Long-term observations (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 principal complication. Articular surfaces of the cryopreserved allografts underwent degenerative changes over five years. These degenerative changes were also manifested radiologically and appeared similar to those observed in humans. By contrast, fresh osteoarticular allografts healed poorly through fibrous union. However, in one of two fresh allografts, the articular cartilage remained intact five years after transplantation.