Bucket-handle tear (BHT) of the medial meniscus accompanying an ACL rupture
By Russell W. Chapin, MS4, Brian E. Reeves, MD, and Thomas Lee Pope, Jr., MD, FACR
Findings
A sagittal T2-weighted MR image of the left knee showed a ruptured
anterior cruciate ligament (ACL) and a large suprapatellar effusion
(Figure 1). A more medial sagittal T1-weighted image of the left
knee showed a curvilinear low-signal-intensity band paralleling the
posterior cruciate ligament (PCL), called the "double PCL" sign
(Figure 2). More medially located sagittal images showed a
high-signal area between the anterior and posterior portions of the
low-signal medial meniscus, called the "absent bow-tie" sign
(Figure 3). A coronal T1weighted image showed the bucket-handle
tear with the main portion of the medial meniscus seen as a
truncated wedge (Figure 4).
Discussion
A BHT is a longitudinal tear of the medial or lateral knee meniscus
that extends from the posterior horn toward the anterior horn.
Bucket-handle tears are usually precipitated by trauma, and up to
40% are associated with an ACL injury, as seen in Figure
1.
1,2 Medial meniscus tears account for 60% to 90% of
BHTs,
1,3 and there are reports of medial and lateral
BHTs in the same knee.
2,4 The radiographic diagnosis of
a BHT is important because BHTs comprise 10% of all meniscal tears
and usually require arthroscopic or surgical repair to prevent
degenerative change.
1-3 Since the plane of a BHT is
parallel to standard sagittal MRI views, the diagnosis relies more
on altered meniscal morphology rather than on changes in signal
intensity.
3 Two classic secondary MRI signs of a BHT are
the double PCL sign and the absent bow-tie sign.
The double PCL sign represents the posterior portion of the
bucket handle, which is still attached to the main meniscal body
but slides over the medial tibial eminence to lie in front of the
PCL in the intercondylar notch (Figure 2).5 When the ACL
is intact, this sign is specific for a medial meniscal tear,
because the course of the ACL prevents lateral meniscus fragments
from lying in the intercondylar notch.1 However, in a
patient with a prior or simultaneous interruption of the ACL, a
lateral bucket-handle tear can also produce the double PCL
sign.4 In the series that first described this sign,
Weiss et al6 reported 100% sensitivity and specificity,
with 7 cases and 47 controls. Subsequent studies have shown that
the double PCL sign is very specific (>98%), but that it is only
approximately 33% sensitive (27% to 44%).1-4,7 Other
low-signal structures that can be present in the intercondylar
notch and must be differentiated from the double PCL sign include
the ligament of Humphrey, a torn ACL, fracture fragments,
osteophytes, or loose bodies.5
In sagittal MRI of the knee, a bow-tie appearance is created by
the anterior and posterior horns of the meniscus, which are seen as
touching low-signal-intensity triangles. With 4- to 5-mm sagittal
slices, a normal meniscus, which is 9- to 12-mm wide, should look
like a bow tie on at least 2 consecutive images.4 When a
BHT forces the central portion of the meniscus into the
intercondylar notch, the knot of the bow tie disappears. Thus, the
absent bow-tie sign, as defined by Helms et al,4 is the
continuity of the anterior and posterior meniscal portions in none
or only one sagittal image. In the images presented in this case,
the anterior and posterior horns of the medial meniscus are
discontinuous and the bow-tie sign is absent (Figure 3). The absent
bow-tie sign has been shown to have a sensitivity of approximately
90% (71% to 98%) and a specificity of approximately
63%.2-4,7 The presence of this sign can also be due to
congenitally hypoplastic or ring-shaped menisci, small menisci (in
children and petite adults), partial meniscectomy, or arthritic
degeneration.2,4 A discoid meniscus, which has a
thickened body portion, can have the normal bow-tie appearance even
when a BHT is present.3
Other MRI signs of a BHT include a truncated meniscus (Figure 4)
and a fragment in the intercondylar notch in coronal
views.3 A flipped posterior meniscus and double (or
tall) anterior horn are other signs of a BHT on sagittal
images.2,3 When the various radiographic signs are
combined, the overall sensitivity and specificity of MRI for a BHT
exceeds 90%.2,3
- Wright DH, De Smet AA, Norris M. Bucket-handle tears of the
medial and lateral menisci of the knee: Value of MR imaging in
detecting displaced fragments. AJR Am J
Roentgenol.1995;165:621-625.
- Aydingoz U, Firat AK, Atay OA, Doral MN. MR imaging of meniscal
bucket-handle tears: A review of signs and their relation to
arthroscopic classification. Eur Radiol. 2003;13:618-625.
- Dorsay TA, Helms CA. Bucket-handle meniscal tears of the knee:
Sensitivity and specificity of MRI signs. Skeletal Radiol.2003;
32:266-272.
- Helms CA, Laorr A, Cannon WD Jr. The absent bow tie sign in
bucket-handle tears of the menisci in the knee. AJR Am J
Roentgenol.1998;170:57-61.
- Singson RD, Feldman F, Staron R, Kiernan H. MR imaging of
displaced bucket-handle tear of the medial meniscus. AJR AM J
Roentgenol.1991;156:121-124.
- Weiss KL, Morehouse HT, Levy IM. Sagittal MR images of the
knee: A low-signal band parallel to the posterior cruciate ligament
caused by a displaced bucket-handle tear. AJR Am J
Roentgenol.1991;156:117-120.
- Watt AJ, Halliday T, Raby N. The value of the absent bow tie
sign in MRI of bucket-handle tears. Clin
Radiol.2000;55:622-626.
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Bucket-handle tear (BHT) of the medial meniscus accompanying an ACL rupture.
Appl Radiol.
August 04, 2005