The reharvested central third of the patellar tendon. A histologic and biomechanical analysis.

We assessed the histologic, mechanical, and structural properties of the reharvested central-third patellar tendon in greyhounds. Twelve dogs had the central third of the patellar tendon (5 mm) removed with corresponding bone blocks from the patella and tibia; the remaining tendon defect was loosely closed. Six dogs were sacrificed at 6 months and six at 12 months, and the central third of the patellar tendon was harvested from both the operative and the contralateral control knees. Analysis of the structural changes in the tendons revealed a significant increase in thickness for reharvested tendons at both 6 and 12 months when compared with controls. The entire residual tendons were narrower at 6 months and were shorter at 12 months compared with controls. Mechanical testing showed that the average failure load, ultimate tensile strength, strain at failure, and average modulus for the reharvested central third of the patellar tendon were significantly less than that of controls at both 6 and 12 months. Analysis of collagen fiber size by electron microscopy revealed a significant increase in collagen fiber diameter at 6 months (135 +/- 41 nm versus 49 +/- 4 nm) but no difference between the operative limbs and controls at 12 months. The reharvested bone-patellar tendon-bone complex does not have the same properties as the primary patellar tendon graft up to 1 year after harvest in a canine model, and its use for revision cruciate ligament reconstruction must be carefully reexamined.