Image Quiz

Knee Pain and Loss of Motion in a Thirteen-Year-Old Boy (continued)

Answer: Displaced bucket-handle medial meniscal tear

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Fig. 1	Fig. 1-A	Fig. 2
Fig. 1 Sagittal T1-weighted magnetic resonance image demonstrating a low-signal band (denoted by arrow) anterior and parallel to the posterior cruciate ligament (denoted by asterisk). Fig. 1-A Line drawing corresponding to sagittal magnetic resonance image (Fig. 1). The line drawing illustrates the two parallel components of the "double PCL sign"—the displaced meniscus and the posterior cruciate ligament. Fig. 2 Coronal T2-weighted magnetic resonance image revealing flipped central meniscal material (denoted by arrow).
Fig. 3	Fig. 4	Fig. 5
Fig. 3 Coronal T2-weighted magnetic resonance image showing coronal truncation of the peripheral body (denoted by arrow). Fig. 4 Axial T2-weighted magnetic resonance image illustrating the bucket-handle morphology (denoted by arrow). The meniscus forms a shape more closely resembling a football than the letter C. The tear involved the posterior three-quarters of the meniscus. Fig. 5 Intraoperative arthroscopic photograph of the medial compartment, depicting the anterior aspect of the displaced bucket-handle tear of the medial meniscus (denoted by arrow).

The patient was admitted to the hospital and underwent arthroscopy of the right knee the next morning.

Initial inspection through standard arthroscopic portals revealed normal patellofemoral and lateral compartments of the knee. In addition, inspection of the intercondylar notch demonstrated normal anterior and posterior cruciate ligaments. The medial compartment contained a displaced bucket handle tear of the medial meniscus (Figs. 1-5), involving the posterior three-quarters of the meniscus. The tear was peripheral and amenable to repair. Consequently, the meniscal edges were abraded with a rasp, reduced, and secured with four anchors. With the knee in full flexion, and then in full extension, the meniscal repair was found to be stable. The patient was discharged that same day with a hinged knee brace locked in extension, and he was instructed to walk with toe-touch weight-bearing with crutches.

Ten days postoperatively, the patient was allowed to unlock the brace when sitting. Four weeks postoperatively, the brace was discontinued and the patient began a progressive range of motion and strengthening program under the direction of a physical therapist. Three months postoperatively, physical examination revealed a full painless range of motion. The patient was permitted to return to all activities without restriction.

Discussion

The "double posterior cruciate ligament (PCL)" sign was first reported in 1991 as a "low-signal band anterior and parallel to the posterior cruciate ligament on sagittal magnetic resonance images" caused by a displaced bucket-handle tear of the medial meniscus¹. In a study that correlated the magnetic resonance imaging and arthroscopic findings of 107 knees, it was reported that the "double PCL sign" had a sensitivity of 32% and a specificity of 98%². Similarly, a retrospective study that compared the findings from seventy-one magnetic resonance images of the knee to the findings at arthroscopy showed a sensitivity of 32.6% and a specificity of 100%³for the "double PCL" sign.

Other magnetic resonance imaging signs of a meniscal bucket-handle tear in arthroscopically proven cases include a central meniscal fragment, the absent bow tie sign, and the coronal truncation sign^2-4. The body of the meniscus averages 9 to 12 mm in width, and standard sagittal (4 to 5 mm-thick) images should reveal the meniscal body segments (bow ties) on two successive cuts³. Therefore, an absent "bow tie" sign is defined as the presence of only one or no meniscal body segments (bow ties) in consecutive peripheral sagittal magnetic resonance images⁵. A coronal truncation sign is considered positive if coronal images demonstrate an amputated, deformed meniscus with a deficient body⁴.

*The authors did not receive grants or outside funding in support of their research for or preparation of this manuscript. They did not receive payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.

References

1. 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;156:117-9.
2. Watt AJ, Halliday T, Raby N. The value of the absent bow tie sign in MRI of bucket-handle tears. Clin Radiol. 2000;55:622-6.
3. Dorsay TA, Helms CA. Bucket-handle meniscal tears of the knee: sensitivity and specificity of MRI signs. Skeletal Radiol. 2003;32:266-72.
4. 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;13:618-25.
5. 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.