Imaging diagnosis
Case 158
【Progress】
She was transported to the hospital where endoscopic surgery is served to manage the meniscus tear.
【Discussion】
Bucket handle tear is the most advanced type of the longitudinal tear. It can happen at either the medial meniscus or the lateral meniscus. The configuration formed by both of the flipped meniscus and the remained meniscus looks like a bucket handle (1, 2). The total bucket handle tear implies the whole longitudinal tear from anterior horn to posterior horn through the body part. The partial bucket handle tear remains intact anterior horn or posterior horn. Irrespective of the whole longitudinal tear or the partial, the flipped meniscus moves to the center. Then, it is the key for diagnosis of the bucket handle tear to interpret the presence of the flipped (separated) fragment from the meniscus body on MRI (3-5). In our case, the MRI axial images of the right knee showed the partial bucket handle tear of the lateral meniscus (Fig. 8).
In medial meniscus, posterior horn is larger than anterior horn, while in lateral meniscus, posterior horn is the same size as anterior horn. The MRI coronal and sagittal images show the appearance of bow tie irrespective of lateral meniscus and medial meniscus (6). The presence of many bow ties implies a discoid meniscus (7). Whereas, the absent bow tie sign implies the volume loss of posterior horn or anterior horn, indicating meniscus tear (2, 3). It includes a bucket handle tear. In our case, MRI showed the absent bow tie sign (Figs. 2C and 3B) due to less volume of the posterior horn in the lateral meniscus indicative of meniscus tear. At the same time, two bow ties are demonstrated on the coronal MRI (Fig. 2): one bow tie implies the intact anterior horn and another bow tie implies the separated fragment from the meniscus body. Actually, at first two bow ties confused us and nearly mis-interpreted the tear of discoid meniscus.
Double posterior crus ligament (PCL) sign implies the flipped fragment lies inferior and anterior to the PCL. It is usually reported to occur in the case of bucket handle tear of meniscus (1, 2). But in our case with a bucket handle tear of lateral meniscus, MRI showed no double PCL sign but the flipped fragment lied lateral and inferior to the anterior crus ligament (ACL). The attachment of ACL to the tibia is a little lateral compared the attachment of PCL (Figs 6, 7, 8). Namely, although no report was documented, it should be that double PCL sign appears in case of bucket handle tear of medial meniscus because the flipped fragment moves medial and anterior to the PCL. Meanwhile, it should be no double PCL sign in the case of bucket handle tear of the lateral meniscus. In our case the separated fragment from the meniscus body was shown on MRI (Figs 2C, 4C, 5C, 9B, 9C, 9D, 9E). The separated fragment of lateral meniscus lies lateral and posterior to the ACL (Figs 9B, 9C, 9D, 9E).
【Summary】
We present a twenty year-old female suffering from difficulty of the extension of the right knee called ‘locking’. The right knee MRI showed the absent tie bow sign of the lateral meniscus indicating meniscus tear and at the same time two bow ties on coronal images. One bow tie indicated the intact anterior horn and another one indicated the flipped fragment separated from meniscus body, implying diagnosis of bucket handle tear. It is borne in mind that bucket handle tear is categorized into whole bucket handle tear and partial bucket handle tear. The key of findings of making diagnosis on MRI is to find the displaced fragment teared from meniscus. The double PCL sign implies the bucket handle tear of the medial meniscus but not of the lateral meniscus tear (actually not found in our case due to the lateral meniscus bucket handle tear). In the lateral meniscus bucket handle tear, the fragment appears more lateral and posterior to ACL. Further, although the tibial bone origin of ACL and PCL situate at the center of the knee, PCL situate a little more medially than ACL. That is why double PCL sign appears in the case of medial meniscus bucket handle tear but not lateral meniscus bucket handle tear.
【References】
1.Camacho, MA . The double posterior cruciate ligament sign. Radiology 2004；233: 503–504.
2.Helms, CA, et al. The absent bow tie sign in bucket-handle tears of the menisci in the knee. AJR Am J Roentgenol 1998;170(1): 57–61.
3.Ruff, C, et al. MR imaging patterns of displaced meniscus injuries of the knee. AJR Am J Roentgenol 1998;170(1): 63–67
4.Vande Berg, BC, et al. Meniscal tears with fragments displaced in notch and recesses of knee: MR imaging with arthroscopic comparison. Radiology 2005; 234: 842–850.
5.McKnight, A, et al. Meniscal tears with displaced fragments: common patterns on magnetic resonance imaging. Skeletal Radiol 2010; 39: 279–283.
6.Lieberman, KA . The absent bow tie sign. Radiology 2000; 215: 263–265.
7.Samoto N, et al. Diagnosis of discoid lateral meniscus of the knee on MR imaging. (2002) Magnetic resonance imaging. 2002; 20: 59-64
2019.8.21