RESUMO
PURPOSE: In this vivo animal study, the authors evaluated the effect of thermal shrinkage on the rabbit patellar tendon using modified approaches involving intra-tendinous thermal treatment and protective immobilization. METHODS AND MEASURES: Of 30 New Zealand white rabbit patellar tendons, Twenty-five rabbits underwent tendon immobilization by fixation of the patella to the femur after thermal shrinkage of the right-side patellar tendon. Ten rabbits of those were sacrificed at 4 weeks and the other fifteen rabbits at 8 weeks. The left-side patellar tendon of twenty-five rabbits were underwent sham-control except thermal treatment. The rate of shrinkage and maximal peak stress and linear stiffness by unit area were assessed in these twenty-five rabbits. Differences between groups were statistically analyzed. Light and transmission electron microscopy examination were evaluated in all of thirty rabbits. RESULTS: The shrinkage rate immediately after thermal treatment did not change significantly at 4 and 8 weeks. The mean maximal tensile stress and linear stiffness at 8 weeks (372.30+/-164.37 N/m2 and 214.60+/-142.52 N/mm) were significantly higher than those measured at 4 weeks (233.84+/-91.12 N/m2 and 196.70+/-72.10 N/mm, respectively) allthough those were diminished when it compared with those of sham control group. Numerous collagen fibers with medium diameters and myofibroblasts indicative of a healing process were observed on histologic examination at 8 weeks. CONCLUSION: Intra-tendinous thermal shrinkage combined with a period of protective immobilization may be one of positive concern for prevention of re-stretching phenomenon as time goes by.