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.

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.

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.

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.