Clinical History: 35 year old male with medial knee pain and locking. Gradient-echo sagittal (1a,1b) and STIR coronal (1c) images are provided. What are the findings? What is your diagnosis?
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Figure 1:
Gradient-echo sagittal (1a,1b) and STIR coronal (1c) images
Findings
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Figure 2:
The gradient echo sagittal images (2a,2b) reveal non-visualization of the meniscal body, despite the fact that the slices lie at the periphery of the medial tibia. On image b, the anterior horn of the medial meniscus (arrow) appears larger than the posterior horn, which should never be the case in normal individuals.
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Figure 3:
(3a) The inversion-recovery coronal exam demonstrates a large displaced meniscal fragment (arrow) along the medial aspect of the intercondylar notch.
Diagnosis
Bucket-handle tear of the medial meniscus.
Discussion
Bucket-handle tears are so named because the inner rim of the meniscus pulls away from the residual meniscal body, resulting in a longitudinal tear pattern that resembles the shape of a bucket.
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Figure 4:
(4a) Schematic representation of a bucket-handle tear of the medial meniscus demonstrates the typical displacement of the inner rim of the meniscus (arrows), creating the handle of the bucket.
Bucket-handle tears are quite important clinically, as locking of the joint often occurs, necessitating arthroscopic treatment of the tear. Unfortunately, bucket-handle tears of the meniscus are one of the more frequently missed tear patterns with MR imaging.
The “Bow-tie Rule”1,2 is a useful MR interpretation sign that should increase a reader’s sensitivity for the detection of bucket-handle tears. The bow-tie rule, simply stated, is that the normal meniscal body should be seen as at least two consecutive “bow-ties” on consecutive sagittal images. The rule is effective because the normal meniscal body is 10-12mm in width, and thus routine 4mm sagittal slices will typically result in two slices through the meniscal body. These images through the normal meniscal body have a bow-tie appearance in the sagittal plane.
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Figure 5:
(5a) Consecutive sagittal images through a normal medial meniscus demonstrate the expected appearance of the 2 normal "bow-ties" that depict the meniscal body.
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Figure 6:
(6a) With bucket-handle tears, meniscal tissue is pulled away from the meniscal body, effectively reducing the width of the body. As a result, consecutive sagittal slices through the region of the body will no longer result in two bow-tie like images.
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Figure 7:
(7a) Sagittal proton density weighted image from another patient reveals a lack of bow-ties (arrow) at the periphery of the medial tibia, suggesting the presence of a bucket-handle tear.
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Figure 8:
(8a) The displaced bucket-handle fragment (arrow) is confirmed on a midline sagittal image.
Conclusion
Whenever absent bow-ties are noted on the sagittal images of the knee, you should carefully review the coronal and axial views for the displaced meniscal tissue that is frequently present. Although the displaced “handle” of the bucket is often visible, it can at times be difficult to see because of edema within the fragment. In such cases, the lack of two consecutive bow-ties on sagittal images may be your best clue for the detection of a bucket-handle tear.
1 The absent bow-tie sign in bucket-handle tears of the menisci in the knee. CA Helms, A Laorr, and WD Cannon, Jr. AJR 1998; 170:57-61.
2 The absent bow-tie sign. KA Lieberman. Radiology 2000; 215:263-265.