Collagen Fibril Organization in the Patellar Tendon Autograft After Posterior Cruciate Ligament Reconstruction: A Quantitative Evaluation in a Sheep Model

We replaced the posterior cruciate ligament in 30 skel etally mature sheep with a patellar tendon autograft using the central third of the ipsilateral patellar tendon. The healing autograft was compared with the contralat eral posterior cruciate ligament and the patellar tendons and posterior cruciate ligaments of nonoperated ani mals. The collagen fibril diameters were analyzed using transmission electron photomicrographs of fibril cross sections taken at six periods during the 2 years after surgery. The patellar tendon and posterior cruciate liga ment were characterized by a broad, nongaussian dis tribution of collagen fibril diameters. The autografts shifted to a unimodal distribution by an increase of small-diameter collagen fibrils. The frequency of small- diameter fibrils measuring up to 100 nm was 99% after 2 years. At that time, these small-diameter fibrils rep resented 91.6% of the area covered by collagen fibrils. The mean diameter of the collagen fibrils in the au tografts significantly decreas...