Biomechanical and histological properties of the canine patellar tendon after removal of its medial third.

Three groups of dogs were used for this study. All dogs had the medial third of the patellar tendon removed from one knee, while the contralateral knee was used as a control. The time zero group was immediately sacrificed; the other two groups were sacrificed at 3 and 6 months. Once the tissues were harvested, the patellar tendon was isolated and biomechanical and histologic analyses were conducted. Three and 6 months after surgery, there was a large amount of visible scar tissue in the tendon. The cross-sectional area of the tendons was 275% and 288% of controls at 3 and 6 months, respectively. The tensile modulus of the tendon was statistically less than controls at both 3 and 6 months. The energy to failure and stiffness of the operated tendons were not statistically different than controls at 3 or 6 months after surgery. The results of this study directly contrast with those of an earlier study of the removal of the central third of the patellar tendon. While a number of factors could explain differences observed between removal of a central or medical third, this study confirms the short-term damaging effects of surgical removal of a portion of the patellar tendon to reconstruct a torn anterior cruciate ligament.