The Effects of Immobilization on Biomechanical and Morphological Properties of Patellar Tendon in Rabbits

ABSTRACT

PURPOSE: For the study for patellar tendon which can be a cause of joint stiffness and weakness, we analysed the biomechanical and the histological changes of patellar tendon according to each immobiliza-tion period after cast immobilization of knee joint of rabbits. MATERIALS AND METHODS: The knee joints of 36 rabbits were immobilized with long leg cast and K-wire fixation for 4, 8, 12, and 16 weeks. The tensile tests were carried out on 6 pairs of the patellar ten-dons obtained from the rabbits which were immobilized for each periods, and the histological study was done for 3 pairs of patellar tendons. RESULTS: The immobilization changed the mechanical properties of the patellar tendon significantly; it decreased the tangent modulus and tensile strength to 26 percent of control values after 16 weeks immo-bilization. The cross-sectional area and tendinous length were not changed significantly. Remarkable changes were also observed in the histologic properties; histological studies showed that the immobiliza-tion has increased the number of fibroblasts and decreased the longitudinally aligned collagen bundles. CONCLUSIONS: These results imply that mechanical weakness and histological changes of patellar tendon due to cast immobilization are one of the causes of stiffness and weakness of knee joint after cast immo-bilization.