Effect of freeze‐drying or γ‐irradiation on remodeling of tendon allograft in a rat model

Freezing or freeze‐drying and γ‐irradiation are techniques currently 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 loss of collagen labeled with a radioactive isotope. The grafts were divided into the following four groups according to the processing method: fresh‐frozen, freeze‐dried, fresh‐frozen and γ‐irradiated, or freeze‐dried and γ‐irradiated. The percentage of donor collagen, calculated from hydroxyproline content and radioactivity level, was used as an indicator of graft remodeling. At 2 weeks, the level of donor collagen 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‐dried and irradiated group, 44%. At 4 weeks, the percentage of donor collagen 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 12 weeks, the levels were 19% in the fresh‐frozen group, 20% in the freeze‐dried group, 15% in the fresh‐frozen and irradiated group, and 6% in the freeze‐dried and irradiated group. The percentages of donor collagen in the freeze‐dried and the fresh‐frozen and irradiated groups were significantly lower than that in the fresh‐frozen group at 4 weeks. The values for the freeze‐dried and irradiated group were significantly lower than those for the fresh‐frozen and irradiated group at 4 and 12 weeks. These data suggest that freeze‐drying, freeze‐drying followed by γ‐irradiation, and fresh‐freezing followed by γ‐irradiation temporarily accelerate graft remodeling.