Disproportionate posterior horn sign (meniscal tear)
The disproportionate posterior horn sign is a feature described with a meniscal tear having a posteriorly flipped fragment.
Bucket handle tears of meniscus of the knee joint constitute 10% of meniscal tears. They consist of a vertical or longitudinal tear (which includes vertical-oblique tears also) extending from the posterior horn through the body segment and into the anterior horn. This occurs due to sudden impact injuries splitting the meniscus.
The inner smaller fragment displaces into the central compartment towards the intercondylar notch of the knee and can be seen to lie in the parasagittal plane producing the double PCL sign.
However, when bucket handle fragments are predominantly involving the anterior-body segment or posterior-body segment of the meniscus, these displace and lie over the posterior or anterior meniscus either giving a doubled-up appearance or a disproportionately large horn. This defines the 'flipped meniscus sign' or the 'flipped fragment sign'.
The flipped meniscus, when displaced anteriorly, demonstrates the 'double anterior horn sign', and when displaced posteriorly it conforms to the 'disproportionate posterior horn sign'.