Biomechanical and histological changes in the patellar tendon after in situ freezing An experimental study in rabbits

OBJECTIVE: The effects of freezing on the remodelling process of the patellar tendon were examined. DESIGN: An experimental study in rabbits. BACKGROUND: Patellar tendon weakens when grafted as a subsstitute for the anterior cruciate ligament. Fibroblast necrosis is considered to be one of the many factors contributing to this change. Therefore, the effect of freeze-induced necrosis on the patellar tendon has been studied. METHODS: Using a technique for freezing the patellar tendon in situ with liquid nitrogen to kill fibroblasts, we studied the biomechanical and histological changes in the patellar tendon up to 24 weeks after freezing. RESULTS: The cross-sectional area started to increase by week 3, reaching a plateau by week 12. The elastic modulus and tensile strength began decreasing by week 3. Although the maximum load decreased at weeks 12 and 24, the stiffness did not change. Histologically, cells were absent until week 2. Athough cells were apparently normal at week 24, there were none of the dense collagen bundles that are normally seen. CONCLUSIONS: The once-frozen patellar tendon weakens as tissue remodelling occurs. RELEVANCE: The study was designed to ascertain whether the remodelling process of the once-frozen patellar tendon coincides with its mechanical properties in different phases. The weakening of the patellar tendon occurred as new cells proliferated into the tendon and remodelled the tissue.