Double PCL sign is the most common described sign around the intact PCL. It occurs due to the displaced fragment of BHT of medial meniscus lying parallel and antero-inferior to the PCL.
Sensitivity is the ability to correctly identify the disease (true positive rate), whereas specificity is the ability to correctly identify those without the disease (true negative rate).
What may be the clinico- radiological importance of this sign and its variants?
Double PCL sign may be seen on sagittal MRI image of knee when the bucket handle fragment of the medial meniscus tilts towards the centre of the joint and comes to lie anterio-inferior to intact PCL. Integrity of ACL is necessary for this sign to appear as it prevents further flipping of the meniscal fragment away from knee centre.
Interestingly,in some patients BHT of lateral meniscus with ACL tear can also lead to this sign.
Sensitivity: 27%–53%[earlier considered 100%]
Specificity:98%-100%
Other mimics-presence of meniscofemoral ligament(of Humphrey) or oblique menisco-meniscal ligament.One must trace the course.