736 The Human Posterior Cruciate Ligament Complex: An Interdisciplinary Study Ligament Morphology and Biomechanical Evaluation* Christopher D. Harner,† MD, John W. Xerogeanes, MD, Glen A. Livesay, MS, Gregory J. Carlin, MS, Brian A. Smith, MD, Takeshi Kusayama, MD, Shinji Kashiwaguchi, MD, and Savio L-Y. Woo, PhD From the Musculoskeletal Research Center, Department of Orthopaedic Surgery, University of Pittsburgh, Pittsburgh, Pennsylvania ABSTRACT To study the structural and functional properties of the human posterior cruciate ligament complex, we meas- ured the cross-sectional shape and area of the anterior cruciate, posterior cruciate, and meniscofemoral liga- ments in eight cadaveric knees. The posterior cruciate ligament increased in cross-sectional area from tibia to femur, and the anterior cruciate ligament area de- creased from tibia to femur. The meniscofemoral liga- ments did not change shape in their course from the lateral meniscus to their femoral insertions. The pos- terior cruciate ligament cross-sectional area was ap- proximately 50% and 20% greater than that of the an- terior cruciate ligament at the femur and tibia, respectively. The meniscofemoral ligaments averaged approximately 22% of the entire cross-sectional area of the posterior cruciate ligament. The insertion sites of the anterior and posterior cruciate ligaments were evalu- ated. The insertion sites of the anterior and posterior cruciate ligaments were 300% to 500% larger than the cross-section of their respective midsubstances. We determined, through transmission electron microscopy, fibril size within the anterior and posterior cruciate liga- ment complex from the femur to the tibia. The posterior cruciate ligament becomes increasingly larger from the tibial to the femoral insertions, and the anterior cruciate ligament becomes smaller toward the femoral insertion. We evaluated the biomechanical properties of the femur-posterior cruciate ligament-tibia complex using 14 additional human cadaveric knees. The posterior cruciate ligament was divided into two functional com- ponents : the anterolateral, which is taut in knee flexion, and the posteromedial, which is taut in knee extension. The anterolateral component had a significantly greater linear stiffness and ultimate load than both the postero- medial component and meniscofemoral ligaments. The anterolateral component and the meniscofemoral liga- ments displayed similar elastic moduli, which were both significantly greater than that of the posteromedial com- ponent. During the last 20 years, the major emphasis in the study of knee ligament injuries has focused on the ACL. This is primarily because of the predominance of ACL injuries in both the athletic and general populations. In the United States alone, approximately half a million significant ACL injuries occur annually.’ Because of the ACL’s poor ability to heal, 40,41 most articles have concentrated on techniques for ligament reconstruction. With time, it has become evi- dent that information regarding the anatomic, biomechani- cal, and kinematic properties of the native ACL is neces- sary to select the most suitable replacement graft and to design proper reconstruction techniques. As we learn more about the ACL, the functional importance of the posterior cruciate ligament (PCL) becomes increasingly apparent. Just as the ACL is considered to be the primary restraint to anterior translation of the tibia, the PCL is the primary restraint to posterior translation of the tibia throughout the full range of knee flexion.5, 16,31 The PCL is also recognized by many authors as the primary stabilizer of the knee joint.6,27,31 It is well documented that PCL insufficiency can lead to progressive laxity of secondary stabilizers of the knee, resulting in localized pain, swelling, and insta- lJlhty.3’25-27,49 Posterior cruciate ligament insufficiency has also been shown to lead to changes in both medial and patel- lofemoral compartment pressureS4’ and subsequent degen- erative osteoarthrosis of these compartments.25,42 *Presented at the 20th annual meeting of the AOSSM, Palm Desert, California, June 1994 tAddress correspondence and reprnt requests to Chnstopher D Harner, MD, University of Pittsburgh, Department of Orthopaedics, E1641 Bioscience Tower, Pittsburgh, PA 15213 3 No author or related mstitufion has received any fmancial benefit from re- search m this study. See &dquo;Acknowledgments&dquo; for funding information.