EFFECT OF FREEZE-DRYING OR GAMMA-IRRADIATION ON REMODELING OF TENDON ALLOGRAFT IN A RAT MODEL

Freezing or freeze-drying and gamma-irradiation are techniques current ly used for processing tendon allografts. However, it is still unknown how these processing methods affect graft remodeling. In this study, we used a rat patellar tendon transplantation model to investigate the effect of various processing methods on remodeling by quantifying los s of collagen labeled with a radioactive isotope. The grafts were divi ded into the following four groups according to the processing method: fresh-frozen, freeze-dried, fresh-frozen and gamma-irradiated, or fre eze-dried and gamma-irradiated. The percentage of donor collagen, calc ulated from hydroxyproline content and radioactivity level, was used a s an indicator of graft remodeling. At 2 weeks, the level of donor col lagen in the fresh-frozen group was 62%; in the freeze-dried group, 59 %; in the fresh-frozen and irradiated group, 57%; and in the freeze-dr ied and irradiated group, 44%. At 4 weeks, the percentage of donor col lagen remaining in grafts decreased to 38% in the fresh-frozen group, 19% in the freeze-dried group, 27% in the fresh-frozen and irradiated group, and 12% in the freeze-dried and irradiated group. Finally, at 1 2 weeks, the levels were 19% in the fresh-frozen group, 20% in the fre eze-dried group, 15% in the fresh-frozen and irradiated group, and 6% in the freeze-dried and irradiated group. The percentages of donor col lagen in the freeze-dried and the fresh-frozen and irradiated groups w ere significantly lower than that in the fresh-frozen group at 4 weeks . The values for the freeze-dried and irradiated group were significan tly lower than those for the fresh-frozen and irradiated group at 4 an d 12 weeks. These data suggest that freeze-drying, freeze-drying follo wed by gamma-irradiation, and fresh-freezing followed by gamma-irradia tion temporarily accelerate graft remodeling.