MR Imaging of the Meniscus: Review, Current Trends, and Clinical Implications

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MR imaging is the preferred imaging modality for evaluating the meniscus. Overall, when strict criteria are followed, it is accurate in diagnosing meniscal tears in patients who have not had prior meniscal surgery. However, an accurate interpretation requires a through knowledge of the normal meniscal anatomy, common meniscal variants, and common diagnostic pitfalls. In this article, the author emphasizes the importance of describing meniscal tears properly and discusses treatment options. Diagnosing a recurrent tear is more complicated in patients who have had prior partial meniscal resection or repair, and the use of MR arthrography in this group of patients is discussed. Recent developments in areas such as 3 T and parallel imaging offer promise for accurate meniscal evaluation with even shorter scan times.

Section snippets

Anatomy

The menisci are wedge-shaped, semilunar (C-shaped), fibrocartilage structures composed of thick collagen fibers primarily arranged circumferentially, with radial fibers extending from the capsule, between the circumferential fibers. The superior surface of the meniscus is concave and the inferior surface is flat, allowing for maximal congruency between the femur and tibia. With weight bearing, the curved femoral condylar surfaces radially displace the menisci, creating circumferential hoop

Meniscal variants

Many meniscal variants have been reported. Some of the variants described more commonly include the discoid meniscus, meniscal ossicles, and the meniscal flounce.

The discoid lateral meniscus has a reported incidence of 0.4% to 16.6% and is more common in the Japanese and Korean populations (Fig. 3) [9]. Joint line tenderness is noted in 73%, “snapping” in 49%, and locking of the knee in 21% of patients [10]. The three types of discoid lateral meniscus are complete, incomplete, and the Wrisberg

Meniscal extrusion

Meniscal extrusion is measured from the outer meniscal edge to the proximal tibial margin. Extrusion of the medial meniscus more than 3 mm is considered abnormal (Fig. 5). This degree of extrusion can be seen in patients who have advanced meniscal degeneration, and various types of meniscal tears [22]. Although extrusion of the anterior horn or body of the lateral meniscus sometimes is considered a normal variant [23], others consider extrusion of the lateral meniscus more than 1 mm to be

Tears: etiology

The cause of meniscal tears can be divided into two categories: increased force on a normal meniscus, usually resulting in longitudinal or radial tears, and normal forces on a degenerative meniscus, usually producing horizontal tears in the posterior half of the meniscus [26]. Tears are more common in the medial meniscus [1], [6], possibly because the medial meniscus is less mobile, and it bears more force during weight-bearing than the lateral meniscus [22], [27], with 56% of tears involving

Tears: diagnosis

The diagnosis of a meniscal tear requires high spatial resolution and an optimized signal-to-noise ratio [31], achieved with the use of a dedicated extremity coil, a slice thickness of 3 to 4 mm, a field of view of 16 cm or less, and a matrix size of at least 256 × 192 (frequency and phase). Many MR sequences have been used to evaluate for meniscal tears, and although they vary in other parameters, they all share a short echo time (TE) [32]. The advantages of a short TE include a reduction in

Horizontal tears

Horizontal or cleavage tears are parallel to the tibial plateau and divide the meniscus into upper and lower segments (Fig. 7, Fig. 8) [28].

Vertical tears

A vertical longitudinal tear occurs between the circumferential collagen fibers, parallel to the long axis of the meniscus, perpendicular to the tibial plateau, with the tear equidistant from the peripheral edge of the meniscus (Fig. 9, Fig. 10) [28].

A vertical radial tear occurs on a plane perpendicular to the long axis of the meniscus and perpendicular to

Meniscal pitfalls

Seventy percent of false-positive MR imaging findings occur in the posterior horns of the menisci, which are the most difficult areas to evaluate at arthroscopy [29], [52], [71], [72]. The standard arthroscopic technique for evaluating the posterior horn of the medial meniscus is to probe the tibial surface while compressing the femoral surface [52]. Because evaluation of the meniscal gutters is also difficult, the accuracy of arthroscopy for diagnosing meniscal tears is 69% to 98%, depending

Meniscocapsular separation

Meniscocapsular separation occurs when the meniscus detaches from the capsular attachments [82], which is more common medially and usually is associated with other injuries [83]. The medial capsuloligamentous structures can be thought of as three layers, from superficial to deep: layer 1: crural fascia; layer 2: superficial portion of the MCL; and layer 3: capsule and deep portion of the MCL [84]. The medial meniscus is attached to the femur by way of the meniscofemoral ligament, and to the

Findings associated with meniscal tears

The use of indirect signs to increase the accuracy for the detection of lateral meniscal tears has been reported [85]. A torn or absent superior popliteomeniscal fascicle was noted in 31% of patients with, and 4% without, lateral meniscal tears [86]. Presumptive subarticular stress reactions of the knee are characterized by an edema-like pattern in the subarticular marrow, which encompasses a focal, linear, or curvilinear low-signal area. Of these patients, 76% have a meniscal tear in the same

Meniscal cysts

Meniscal cysts are identified on 4% to 6% of knee MR examinations, are located twice as often medially, and may be lobulated or septated in appearance [32], [91], [92]. The cysts can be confined within the meniscus (intermeniscal) or can extend into the adjacent soft tissue (perimeniscal), with the latter more common [93]. The most widely accepted cause of a meniscal cyst is extension of fluid through a meniscal tear [91], with 57% noted in horizontal cleavage and 33% in complex tears with a

MR imaging field strength

Several studies suggest similar accuracy for diagnosing meniscal tears with 0.2 T and 1.5 T MR imaging, although some controversy remains [94], [95]. Undoubtedly, scanning time is longer at lower field strengths, 15 minutes longer at 0.2 T than at 1.5 T in one article [95]. A higher confidence for diagnosing meniscal tears at 1.5 T, compared with 0.2 T, has been reported, with the exception of the posterior horn of the lateral meniscus, likely because of the inherent increased signal-to-noise

Treatment

The four main options for treating meniscal tears are complete meniscectomy, partial meniscectomy, meniscal repair, and conservative treatment without meniscal surgery [28]. The treatment of meniscal lesions depends on many factors, including the type, location, and size of the tear. Initially, meniscal lesions were treated with complete meniscectomy because the importance of the meniscus and its function were not understood well [97], [98]. Unfortunately, complete meniscectomy has been shown

Postoperative imaging

Postoperative imaging of the meniscus is complicated. The standard criteria for a tear has limited diagnostic usefulness when diagnosing a tear at the site of meniscal repair or partial resection, with sensitivity up to 100% but specificity as low as 23% [50], [51], [100], because of either intermeniscal granulation tissue, which can have abnormal T1-weighted or proton density signal extending to the meniscal surface in the repaired or healing meniscus, or the possible “conversion” of grade 1

Future imaging: ultrashort echo time imaging, parallel imaging, and 3 Tesla

Ultrashort TE imaging (TEs of 0.08–0.2 ms) is a technique in which the normal meniscus demonstrates increased signal and tears have decreased signal, and is performed best without fat suppression [118]. In contrast to fat-suppressed T1 and Fast Low Angle Shot (FLASH) sequences with intravenous gadolinium, which cannot differentiate between the vascular and avascular zones of the meniscus [4], contrast administration on ultrashort TE images can make this differentiation [118], [119]. The full

Summary

MR imaging is the preferred imaging modality for evaluating meniscal pathology, with high accuracy reported in most studies. Achieving this high accuracy requires a thorough knowledge of the anatomy of the meniscus and perimeniscal structures, an understanding of normal variants and interpretive pitfalls, an awareness of the common findings associated with meniscal tears, and an understanding of the diagnostic criteria for a meniscal tear. In patients who have partial meniscal resection or

Acknowledgments

I would like to thank D. Laurie Persson and K. Fox for their invaluable assistance in the preparation of the figures and manuscript, respectively.

References (124)

  • R. von Eisenhart-Rothe et al.

    Femoro-tibial and menisco-tibial translation patterns in patients with unilateral anterior cruciate ligament deficiency—a potential cause of secondary meniscal tears

    J Orthop Res

    (2004)
  • T. Soejima et al.

    Anteromedial meniscofemoral ligament

    Arthroscopy

    (2003)
  • M. De Maeseneer et al.

    Medial meniscocapsular separation: MR imaging criteria and diagnostic pitfalls

    Eur J Radiol

    (2002)
  • D.L. Muscolo et al.

    Medial meniscal tears and spontaneous osteonecrosis of the knee

    Arthroscopy

    (2006)
  • M. De Maeseneer et al.

    MR imaging of meniscal cysts: evaluation of location and extension using a three-layer approach

    Eur J Radiol

    (2001)
  • T. Rand et al.

    Comparison of low field (0.2T) and high field (1.5T) MR imaging in the differentiation of torned from intact menisci

    Eur J Radiol

    (1999)
  • A.P. Toms et al.

    Imaging the post-operative meniscus

    Eur J Radiol

    (2005)
  • F. Steenbrugge et al.

    Long-term assessment of arthroscopic meniscus repair: a 13-year follow-up study

    Knee

    (2002)
  • E. Pena et al.

    Finite element analysis of the effect of meniscal tears and meniscectomies on human knee biomechanics

    Clin Biomech (Bristol, Avon)

    (2005)
  • E. Rath et al.

    The menisci: basic science and advances in treatment

    Br J Sports Med

    (2000)
  • D.C. Fithian et al.

    Material properties and structure-function relationships in themenisci

    Clin Orthop Relat Res

    (Mar 1990)
  • K.W. Harper et al.

    Radial meniscal tears: significance, incidence, and MR appearance

    AJR Am J Roentgenol

    (2005)
  • O. Hauger et al.

    Characterization of the “red zone” of knee meniscus: MR imaging and histologic correlation

    Radiology

    (2000)
  • U. Aydingoz et al.

    MR imaging of the anterior intermeniscal ligament: classification according to insertion sites

    Eur Radiol

    (2002)
  • B.Y. Lee et al.

    Incidence and significance of demonstrating the meniscofemoral ligament on MRI

    Br J Radiol

    (2000)
  • R.L. Johnson et al.

    MR visualization of the popliteomeniscal fascicles

    Skeletal Radiol

    (1999)
  • M. Asik et al.

    Discoid lateral meniscus: diagnosis and results of arthroscopic treatment

    Knee Surg Sports Traumatol Arthrosc

    (2003)
  • K. Singh et al.

    MRI appearance of Wrisberg variant of discoid lateral meniscus

    AJR Am J Roentgenol

    (2006)
  • Y. Tachibana et al.

    Discoid medial meniscus

    Arthroscopy

    (2003)
  • E.M. Rohren et al.

    Discoid lateral meniscus and the frequency of meniscal tears

    Skeletal Radiol

    (2001)
  • K.N. Ryu et al.

    MR imaging of tears of discoid lateral menisci

    AJR Am J Roentgenol

    (1998)
  • P. Schnarkowski et al.

    Meniscal ossicle: radiographic and MR imaging findings

    Radiology

    (1995)
  • J.S. Yu et al.

    Meniscal flounce MR imaging

    Radiology

    (1997)
  • B.H. Kim et al.

    Meniscal flounce on MR: correlation with arthroscopic or surgical findings

    Yonsei Med J

    (2000)
  • J.S. Park et al.

    Meniscal flounce on knee MRI: correlation with meniscal locations after positional changes

    AJR Am J Roentgenol

    (2006)
  • C.R. Costa et al.

    Medial meniscus extrusion on knee MRI: is extent associated with severity of degeneration or type of tear?

    AJR Am J Roentgenol

    (2004)
  • T.T. Miller et al.

    Meniscal position on routine MR imaging of the knee

    Skeletal Radiol

    (1997)
  • J.M. Brody et al.

    Lateral meniscus root tear and meniscus extrusion with anterior cruciate ligament tear

    Radiology

    (2006)
  • D.J. Hunter et al.

    The association of meniscal pathologic changes with cartilage loss in symptomatic knee osteoarthritis

    Arthritis Rheum

    (2006)
  • A.J. Hough et al.

    Pathology of the meniscus

    Clin Orthop Relat Res

    (Mar 1990)
  • V. Vedi et al.

    Meniscal movement. An in-vivo study using dynamic MRI

    J Bone Joint Surg Br

    (1999)
  • W.H. Jee et al.

    Meniscal tear configurations: categorization with MR imaging

    AJR Am J Roentgenol

    (2003)
  • A.A. De Smet et al.

    MR diagnosis of meniscal tears of the knee: importance of high signal in the meniscus that extends to the surface

    AJR Am J Roentgenol

    (1993)
  • E.M. Escobedo et al.

    Usefulness of turbo spin-echo MR imaging in the evaluation of meniscal tears: comparison with a conventional spin-echo sequence

    AJR Am J Roentgenol

    (1996)
  • C.A. Helms

    The meniscus: recent advances in MR imaging of the knee

    AJR Am J Roentgenol

    (2002)
  • E.H. Oei et al.

    MR imaging of the menisci and cruciate ligaments: a systematic review

    Radiology

    (2003)
  • A.A. De Smet et al.

    Diagnosis of meniscal tears of the knee with MR imaging: effect of observer variation and sample size on sensitivity and specificity

    AJR Am J Roentgenol

    (1993)
  • A.A. De Smet et al.

    Use of the “two-slice-touch” rule for the MRI diagnosis of meniscal tears

    AJR Am J Roentgenol

    (2006)
  • D.A. Rubin et al.

    MR diagnosis of meniscal tears of the knee: value of fast spin-echo vs conventional spin-echo pulse sequences

    AJR Am J Roentgenol

    (1994)
  • R.M. Kowalchuk et al.

    MRI of the knee: value of short echo time fast spin-echo using high performance gradients versus conventional spin-echo imaging for the detection of meniscal tears

    Skeletal Radiol

    (2000)
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    This article was originally published in Magnetic Resonance Imaging Clinics of North America 15:1, February 2007.

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