MECHANISM OF REMODELING PHENOMENON INDUCED BY FUNCTIONAL ADAPTATION OF THE IN-SITU FROZEN-THAWED PATELLAR TENDON

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1. Methods:(1) For 55 Wistar rats (14-week-old), the right patellar tendon underwent the in situ freeze-thaw treatment to necrotize intrisic fibrblasts of the tendon and the left knees underwent the sham-operation in order to test the hypothesis that extrinsic cells which infiltrate in the necrotized patellar tendon synthesize type-III.(2) We examined the in situ frozen-thawed patellar tendon at 2 to 12 weeks after the treatment with immunohistochemistry and reverse transcription-polymerase chain reaction (RT-PCR) and mechanical evaluations. We also evaluated the effect of the in situ freeze-thaw treatment on viability of instrinsic fibroblasts using a tissue-culture technique.2. Results:(1) Tissue culture showed that no cell outgrowth was observed from all explants of the tendons after the freeze-thaw treatment, while fibroblast outgrowth was observed from 83.0 % of the explants in the non-treated tendon.(2) Immunohistochemical findings showed that positive type-III collagen staining was observed around the extrinsic cells which infiltrate in the necrotized tendon at 3,6, and 12 weeks.(3) In addition, RT-PCR analysis showed that the expression level of type-III procollagen mRNA in the frozen-thawed tendon was significantly higher than that in the sham-operated tendon at 6 and 12 weeks.(4) Mechanical evaluations confirmed that the cross-sectional area of the in situ frozen-ghawed tendon at 6 weeks was significantly greater than that of the sham-operated tendon, while its elastic modulus was significantly lower that that of the sham-operated tendon.3. Conclusion: This study suggested that extrinsic cells which infiltrated in the necrotized patellar tendon synthesize type-III collagen in the physiological mechanical environment. The present study indicated that the increase of type-III collagen in the tendon graft is unavoidable, even if we can avoid depriving the graft of stress.