KNEE ASSESSMENT SERIES PART 13: POSTERIOR SAG SIGN FOR PCL ASSESSMENT Like mentioned yesterday, with a ruptured PCL, your tibia might sag posteriorly on the femur. This is also how you assess for the Posterior sag sign, when you let gravity pull the tibia backwards. Watch out for the presence of this sign if you want to do your ACL assessment, because a ruptured PCL might give you a false negative test outcome with ACL assessment! | Physiotutors