Biomechanical and histological observations of the dog patellar tendon after removal of its central one-third

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Abstract
The use of a central one-third patellar tendon as an autograft for surgical reconstruction of a damaged cruciate ligament is common. Few complications of its use have been reported. However, recent clinical studies indicate that decreased quadriceps strength, decreased range of motion, decreased thigh circumference, and patellofemoral problems can be associated this this procedure. Some of these complications may result from alterations in the biomechanical properties of the remaining patellar tendon. The objective of this study was to examine biomechanically and histologically the fate of the remaining patellar tendon after removal of its central one-third. Three groups of dogs were used for this study. On one knee the central third of the patellar tendon was removed, while the contralateral side was used as a control. One group was immediately euthanized, while the other two groups were euthanized at 3 and 6 months. Control and operated patella-patellar tendon-tibia preparations were harvested and stretched to failure at 100% strain per second. The 3 and 6 months groups had a 10% decrease in length of the operated patellar tendon versus the contralateral control. There was a very significant increase in cross-sectional area of the patellar tendon at 3 months, and a further increase at 6 months. The failure load was 70% of the controls at 3 months and 60% of the controls at 6 months. The stiffness and modulus of the operated tendon within the physiologic range were dramatically reduced to 70% and 33% of controls at 6 months, respectively. These overall results were observed with the central one-third defect closed or left open in surgery. This study indicated that the canine patellar tendon had not fully recovered 6 months after removal of its central third. The biomechanical changes observed in the remaining tendon may help explain the loss of quadriceps strength that has been documented in recent clinical studies after using patellar tendon grafts.

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