Histological examination of frozen autograft treated by liquid nitrogen removed after implantation

Background. Several oncological sterilization methods involving autoclaving, irradiation, or pasteurization have been developed for limb reconstruction of large bone defects fol- lowing tumor excision. Studies involving histological examina- tions of these autografts have all found that osteogenesis occurs slowly. We have used frozen autografts treated by liquid nitrogen for limb reconstruction and have achieved excellent results for bone union. To determine if frozen auto- grafts exhibit early bone remodeling, we investigated the repair processes of the frozen bones. Methods. We analyzed frozen autografts treated by liquid nitrogen, retrieved at a mean of 19.1 months (2-75 months) after implantation because of complications or local tumor recurrence. The specimens were obtained from six patients with a mean age of 36.2 years (8-68 years). The six grafts comprised three osteoarticular grafts, two intercalary grafts, and one joint graft. We histologically reviewed the autograft- containing sections for tumor cell necrosis, evidence of corti- cal repair, the cortical junction, and joint cartilage. Results. Tumor cells were completely eradicated from the frozen bone in all cases. In a specimen retrieved 5 months after implantation, a small area of the bone showed active osteocytes and osteoblasts. In three cases retrieved more than 1 year after implantation, osteocytes and osteoblasts were observed in broad portions of the frozen bones, indicating the onset of osteogenesis in the frozen bone at an early stage. The cortical host-graft junction showed incorporation along with continuity of bone trabeculae. In addition, we were able to fi nd normal chondrocytes on the articular surface. Conclusions. The frozen bone specimens in this study thus showed evidence of newly formed bone and earlier osteogen- esis than has been previously reported. Our results suggest that frozen autografts may be considered one of the most useful recycled materials for biological reconstruction.