Histological and biomechanical observations of the rabbit patellar tendon after removal of its central one-third.

Using 35 Japanese white rabbits, a study was made of tissue regeneration and the mechanical properties of the patellar tendon after removal of its central one-third. After removal of the central one-third of the patellar tendon on one side, in experiment 1 the strength of the entire patellar tendon including the regenerated tissue was compared with that of the patellar tendon on the opposite side with the central one-third removed at the time of killing, and in experiment 2 the strength of only the regenerated tissue was compared with that of the patellar tendon on the opposite side with two-thirds of the medial and lateral sides removed at the time of death. In experiment 1, the maximum load showed no significant difference between the operated side and the control. In one half of the cases, the strength of the operated side including the regenerated tissue was weak, suggesting weakening of the patellar tendon on the residual bilateral sides. In experiment 2, the maximum load of the regenerated tissue was significantly lower than that of the control, the former being 25% of the latter even at 6 months. Histologically, the characteristics of the cells and collagen fibers gradually approached those of normal tissue, but the crimp pattern of the collagen fibers and fibrils was evidently smaller than that of the control. These results indicate that regenerated tissue was still mechanically weak and immature at 6 months.