ABSTRACT
BACKGROUND: Posterior cruciate ligament injuries are often associated with injuries to other structures. The role of the posteromedial structures of the knee in these injuries has received little attention. HYPOTHESIS: The posterior oblique ligament is an important restraint to posterior tibial translation in the posterior cruciate ligament-deficient knee. STUDY DESIGN: Controlled laboratory study. METHODS: Kinematic studies were performed on 10 cadaveric knees to test 3 external loading conditions at 0 degrees , 30 degrees , 60 degrees , and 90 degrees of flexion (134 N posterior tibial load, 10 N x m valgus rotation, and 5 N x m internal rotation). Resulting posterior tibial translation was determined by using a robotic/universal force-moment sensor testing system for (1) intact, (2) posterior cruciate ligament-deficient, (3) posterior cruciate ligament/superficial medial collateral ligament-deficient, (4) posterior cruciate ligament/superficial medial collateral ligament/deep medial collateral ligament/posterior oblique ligament-deficient, and (5) posterior cruciate ligament/superficial medial collateral ligament/deep medial collateral ligament/posterior oblique ligament/posteromedial capsule-deficient knee. RESULTS: When both the superficial medial collateral ligament and deep medial collateral ligament were cut in the posterior cruciate ligament-deficient knee, posterior tibial translation did not increase significantly at any flexion grade under all external loading conditions (P > .05). Additional cutting of the posterior oblique ligament increased posterior tibial translation significantly at 0 degrees , 30 degrees , 60 degrees , and 90 degrees of flexion under posterior tibial load and at all flexion angles tested under valgus or internal tibial load (P < .05). Additional cutting of the posteromedial capsule increased posterior tibial translation only at 0 degrees and 30 degrees in response to a valgus and internal tibial load (P < .05). CONCLUSION: The posterior oblique ligament and posteromedial capsule have a significant role in the prevention of additional posterior tibial translation in the knee with posterior cruciate ligament injury. CLINICAL RELEVANCE: The posterior oblique ligament should be addressed in the patient with combined injuries to the posterior cruciate ligament and the posteromedial structures.
