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 skeletally mature sh eep with a patellar tendon autograft using the central third of the ip silateral patellar tendon. The healing autograft was compared with the contralateral posterior cruciate ligament and the patellar tendons an d posterior cruciate ligaments of nonoperated animals. The collagen fi bril diameters were analyzed using transmission electron photomicrogra phs of fibril cross sections taken at six periods during the 2 years a fter surgery. The patellar tendon and posterior cruciate ligament were characterized by a broad, nongaussian distribution of collagen fibril diameters. The autografts shifted to a unimodal distribution by an in crease of small-diameter collagen fibrils. The frequency of small-diam eter fibrils measuring up to 100 nm was 99% after 2 years. At that tim e, these small-diameter fibrils represented 91.6% of the area covered by collagen fibrils. The mean diameter of the collagen fibrils in the autografts significantly decreased to 45% of the controls at Week 26 a nd remained at this level until the end of this study. The percentage of area covered by collagen fibrils per 1 mu m(2) was 78% of the contr ols 2 years postoperatively. This study suggests that the patellar ten don autograft could not reproduce the collagen fibril organization of the posterior cruciate ligament. This may be a biologic factor respons ible for inconsistent results in posterior cruciate ligament replaceme nt.