Atypically Displaced Meniscal Tears: An Educational Review with Focus on MRI and Arthroscopy

Abstract

This review article on atypically displaced meniscal tears serves as a critical reminder for radiologists and orthopedic surgeons. It highlights and details uncommon lesions that may be overlooked during MRI evaluation and/or arthroscopic exploration. The knowledge of their existence can enable radiologists to critically assess any meniscal abnormality, keeping in mind its possible arthroscopic presentation. This is essential for assisting the surgeon in making an accurate preoperative diagnosis. In fact, these atypical lesions pose great challenges to surgeons in terms of the technical aspects of their treatment. Often, they could require additional arthroscopic portals for their identification or the need for special devices or instrumentations for the repair. Knowing these challenges in advance is thus imperative for properly planning a proficient surgery. The correct diagnosis and description of tear patterns, including extent and location, allow optimal pre-operative planning with the choice of the indicated approach. Radiologists should know how to recognize menisci tears, even with atypical dislocation patterns. Particularly, in the case of 'minus' detection or thickness reduction in a meniscus, the possible displaced fragment should be carefully searched for, even in atypical sites.

Keywords: arthroscopy; diagnostic imaging; knee; magnetic resonance imaging; menisci; tears.

Figure 1

Graphical representation of the most common types of meniscal displacement. (A) Bucket-handle lesion; (B) intercondylar fragments; (C1,C2) horizontal and vertical flaps.

Figure 2

Left knee coronal fat-suppressed PD MR images show a medial meniscus body tear (a) with an open oblique course on the inferior side associated with a meniscal flap (white arrows) displaced inferiorly and trapped between the medial tibial bony surface and medial collateral and capsular–ligamentous complex (red arrows) (b).

Figure 3

Initially, the medial meniscus body (black asterisk) did not present as a visible lesion (a). However, after probing the inferior surface, it was possible to find a displaced flap tear (red asterisk) amenable to partial resection (b). MFC, medial femoral condyle; MTP, medial tibial plateau.

Figure 4

Right knee coronal fat-suppressed PD MR images (a) show a medial meniscus body tear with an open oblique course on the inferior side associated with a meniscal flap (white arrow) displaced inferiorly and trapped between the medial tibial bony surface and medial collateral and capsular–ligamentous complex. Axial image (b) shows the fragment at the level of the posteromedial tibial plateau (red circle). Sagittal images (c) show a normal appearance of the posterior horn (red arrow) with just a minimal defect at its free margin and a slightly hyperintense intrameniscal line.

Figure 5

By lifting the medial meniscus body, it is possible to note a small displaced flap (red asterisk) below the medial tibial plateau (a); with the probe, the flap is mobilized, revealing a full extent large flap of the meniscal body and posterior horn (red asterisk) (b); moving the scope toward the posterior horn it is possible to note a radial tear close to the posteromedial root (black asterisk) (c). MTP, medial tibial plateau; MFC, medial femoral condyle.

Figure 6

Right knee coronal fat-suppressed PD-weighted MR images show a full-thickness radial tear of the medial meniscus posterior root (white arrow) (a) associated with peripheral extrusion of the meniscal body (red arrow) (b). Sagittal T2-weighted image highlights the fibrocartilaginous defect and also shows the complete tear of the posterior cruciate ligament (white arrow) (c). Axial STIR sequence confirms the complete absence of the posterior root of the medial meniscus (white arrow) (d).

Figure 7

By lifting the posterior horn of the medial meniscus (black asterisk) with the probe, a detachment of the posterior root (red asterisk) from the medial tibial plateau (MTP) is found (a). After transosseous repair of the posterior root, the meniscus (black asterisk) becomes reinserted to the anatomical location at the tibial bone (red asterisk) (b). MFC, medial femoral condyle.

Figure 8

Left knee sagittal T2-weighted MR image (a) and coronal fat-suppressed PD MR image (b) show part of the lateral meniscus body (white arrow) dislocated in the popliteal hiatus below the popliteus tendon (yellow arrow) and the rest of the meniscus (red arrow). Coronal fat-suppressed PD MR image (c) shows lateral meniscal body extrusion (red arrow) and the inferior displacement of the meniscal portion (red circle). Bone marrow edema of the lateral tibial plateau and corresponding femoral condyle, together with an articular cortical depression (‘notch sign’—arrowhead in (a)), is also noted.

Figure 9

At the level of the popliteus tendon (P), it is possible to see only a thin remnant of the meniscal body (black asterisk), while most of the meniscal body is missing (white asterisk) (a). By lifting the meniscus remnant (black asterisk), it is possible to note the meniscal body (red asterisk), which is flipped backward and inferiorly in the interior popliteal hiatus (b). After reducing the displaced fragment from the popliteal hiatus (red asterisk), the lesion pattern is clear and can be approached for repair (c). LTP, lateral tibial plateau; LFC, lateral femoral condyle.

Figure 10

Right knee sagittal fat-suppressed T2-weighted MR image (a) shows a complete absence of the posterior horn of the lateral meniscus (white arrow). Coronal fat-suppressed T2-weighted MR image (b) shows the posterior horn meniscal flap (red circle) displaced laterally to the lateral femoral condyle. Two adjacent slices of axial T2-weighted MR images show the meniscal portion (red circle and red arrow) trapped between the popliteus tendon (yellow arrows) and the joint capsule (c,d).

Figure 11

In the lateral compartment, the remnant of the meniscal body is seen (red asterisk) while the posterior horn is missing, allowing visualization of the joint capsule (white asterisk) (a). With the arthroscope in the lateral gutter, the lateral meniscus body and posterior horn (black asterisk) are found between the lateral capsule (LC) and the lateral femoral condyle (LFC) (b). After the reduction in the meniscal portion from the lateral gutter (red asterisk), the meniscal shape is restored and amenable to repair (c). LTP, lateral tibial plateau; LFC, lateral femoral condyle.

Figure 12

Right knee sagittal fat-suppressed PD-weighted MR demonstrates the absence of a part of the meniscal posterior horn (red circle) behind the ACL and below the PCL (a). Coronal fat-suppressed PD-weighted MR shows the extrusion of lateral meniscus body (white arrow) (b).

Figure 13

In the lateral compartment, the lateral meniscus posterior horn (red asterisk) demonstrates an interruption at the level of the posterior root (black asterisk) between the meniscus and the tibia. LTP, lateral tibial plateau; LFC, lateral femoral condyle; ACL, anterior cruciate ligament.

Figure 14

Left knee coronal fat-suppressed PD-weighted MR image (a) and axial T2-weighted MR image (b) show a portion of the lateral meniscus entrapped in the fracture rim of the tibial plateau joint face (white arrows).