Fragment-in-notch sign | Radiology Signs

Answer:

The fragment-in-notch sign is a low-signal band of tissue lying within the intercondylar notch, isointense to normal meniscus on all sequences, representing a displaced bucket-handle meniscal tear whose inner fragment has flipped centrally out of its normal position. It is best appreciated on coronal images, which show the fragment sitting in the notch medial to the tibial spines, while the sagittal images show loss of the normal bow tie configuration of the meniscal body. It is closely related to the double PCL sign, which describes the particular case in which the fragment comes to lie parallel to and beneath the posterior cruciate ligament; that arrangement requires an intact anterior cruciate ligament and is essentially confined to the medial meniscus, whereas a lateral bucket-handle fragment is usually blocked by the ACL from taking up that position and is more often simply seen in the notch. The principal mimic is an osteochondral loose body, which contains marrow or calcified signal, may show a fatty centre, and is usually visible on radiographs.

Why is it called so?

The displaced meniscal fragment is seen lying within the intercondylar notch, where no meniscal tissue belongs.

Pathophysiology

A longitudinal vertical tear separates an inner meniscal fragment that stays attached anteriorly and posteriorly, forming the handle of a bucket. The knee’s rolling and gliding motion, particularly in flexion, can lever this handle out of the joint line and drive it centrally into the intercondylar notch, where it becomes trapped. Because the fragment is fibrocartilage, it retains uniformly low signal on every sequence and is indistinguishable in signal from ligament, which is why it is recognised by position and shape rather than by signal. The remaining peripheral rim is correspondingly narrowed, which is what produces the absent bow tie on sagittal images.

Alternative names: Displaced bucket-handle fragment, notch fragment sign

Other associated named signs: Double PCL sign, absent bow tie sign, flipped meniscus sign, double anterior horn sign, and the disproportional posterior horn sign

References

1. Dorsay TA, Helms CA. Bucket-handle meniscal tears of the knee: sensitivity and specificity of MRI signs. Skeletal Radiol. 2003;32(5):266-72. PMID: 12719929.