Quantified kinematics of the injury to the posterior cruciate ligament: a computer-aided design simulation study

Objective. To quantify the kinematics of the injury to the posterior crucia te and the other major knee ligaments as a function of the knee flexion ang le at the moment of impact. Design. Computer-aided design modelling was used to investigate the strain response of all major knee ligaments during anteroposterior abnormal tibio- femoral translation at 0-90 degrees knee flexion. Background. It is generally believed that the likelihood of injury to the p osterior cruciate ligament following anterior impact is higher in the flexe d knee. However, there are no kinematical studies to quantify this clinical observation or investigate the role of the other knee ligaments in the abo ve situation. Methods. Computer calculations of the individual ligament strain were plott ed against the magnitude of posterior tibial translation. Additionally, the strain rate for each ligament (defined as the ligament strain produced per mm of posterior tibial linear translation) was calculated as the slope of the strain-displacement curve for all tested degrees of knee flexion. Results. The posterior cruciate ligament has been shown to be the primary r estraint to posterior tibial translation in all degrees of knee flexion. Ho wever, at 90 degrees of knee flexion the strain rate of the posterior cruci ate ligament is approximately half that in the fully extended knee and the posterior cruciate ligament is the only ligament to resist posterior tibial translation. Conclusions. The strain behaviour of the posterior cruciate ligament during injury is highly dependent on the knee flexion during the moment of impact . Forced posterior tibial translation in the 90 degrees flexed knee may res ult in isolated posterior cruciate ligament deficit rather than a complex l igament disruption. The strain rate of a ligament as introduced in the pres ent study is a quantified parameter related to the resistance that the liga ment imposes to an abnormal joint movement. Relevance This study provides insight into the differential strain of the k nee ligaments during impacts that result in posterior cruciate ligament inj ury. Studies that quantify the strain behaviour of individual knee ligament s are important to the understanding, diagnosis and prevention of injuries sustained during contact sports and high-energy road traffic accidents. (C) 2001 Elsevier Science Ltd. All rights reserved.