FREEZING INFLUENCES THE HEALING OF RABBIT MEDIAL COLLATERAL LIGAMENT AUTOGRAFTS

Connective tissue allografts are treated commonly with deep freezing t o facilitate their storage in tissue banks and to reduce their immunog enicity, The influence of freezing on the healing of these grafts is u nknown, The effect of an aggressive freezing protocol on ligament graf t healing in a nonimmunogenic autograft model was investigated, The fe moral-medial collateral ligament-tibial complex of the rabbit knee was transplanted orthotopically into the site from which it had just been harvested, The fresh group had their grafts rinsed in normal saline, and the frozen-thawed group had their grafts repetitively frozen-thawe d in liquid nitrogen immediately before reimplantation, The healing of the ligament complexes were evaluated mechanically at intervals as lo ng as 1 year after transplantation. Repeated freezing had little effec t on the initial mechanical behavior of the graft complexes but was fo und to be detrimental to subsequent graft incorporation. The frozen-th awed grafts were weaker than the fresh grafts overall, and this effect persisted over time, The failure load and stress of the frozen-thawed grafts reached only 87% and 75% of that of the fresh grafts after 48 weeks. Because the initial mechanical effects of freezing were minimal , subsequent effects on graft healing must be attributed to factors ot her than gross structural injury, Despite showing almost no signs of d amage to hone-ligament-hone grafts initially, freezing procedures may have important subsequent biologic consequences that may influence the clinical success of stored connective tissue grafts used in ligament reconstruction.