Mr imaging for diagnosis of meniscal tears

1. MR Imaging for
Diagnosis of Meniscal
Tears

2. LEARNING OBJECTIVES
 Identify a meniscal tear on MR images.
 Describe and classify meniscal tears according to
their various subtypes.
 Recognize normal meniscal anatomy and congenital
variants to improve diagnostic accuracy

3. INTRODUCTION
 Accurate and timely diagnosis of a meniscal tear is critical
for reducing morbidity and planning treatment.
 It is well established that meniscal damage predisposes the
adjacent articular cartilage to increased axial and sheer
stress, resulting in early degenerative osteoarthritis

4.  Magnetic resonance (MR) is the preferred
noninvasive imaging modality for evaluating internal
knee derangements.
 MR imaging demonstrates high sensitivity (93% for
the medial meniscus [MM] and 79% for the lateral
meniscus [LM].

5. NORMAL ANATOMY
 The menisci function to absorb shock, distribute
load, assist in joint lubrication, and facilitate nutrient
distribution.
 Wedge-shaped, semilunar, fibro cartilaginous
structures with superior concave surface that
conforms to the femoral condyle and a flat base
that attaches to the tibia via the central root
ligaments.

7.  At MR imaging, the menisci appear as low-signal-
intensity structures. Sagittal images, appear as either
a “bow-tie” structure peripherally or opposing
triangles centrally. Coronal images -- triangular or
wedge-shaped.

9. MEDIAL MENISCUS
 Both horns are triangular in shape and have very
sharp points. The posterior horn is always larger
than the anterior horn.
 The posterior root is immediately anterior to the
posterior cruciate ligament.
 The anterior root has a variable attachment, with
82% of individuals having an attachment on the flat
surface of the tibia anterior to the tibial eminence.

11.  The MM is less mobile because of its peripheral
attachments to the deep fibers of the medial
collateral ligament.
 MM has a more open C-shaped configuration and
increases in width from anterior to posterior.

12. LATERAL MENISCUS
 On sagittal images the posterior horn is higher in
position than the anterior horn. Both horns are
about the same size.
 The lateral meniscus posteriorly comes up high over
the tibial spine to insert near the posterior cruciate
ligament.

14. NORMAL ANATOMIC STRUCTURES
MIMICKING TEARS
 Transverse meniscal ligament
 Meniscofemoral ligaments (MFLS)
 Popliteomeniscal fascicles
 Meniscomeniscal ligament.

15.  Transverse meniscal ligament, also called the
geniculate ligament extends from the anterior horn
of the medial meniscus to the anterior horn of the
lateral meniscus.
 At the attachment of the ligament onto the superior
surface of the anterior horn of the lateral meniscus,
there is commonly a high-signal-intensity line. This
line can be mistaken for an anterior horn tear.

17.  Meniscofemoral ligament originate from the
posterior horn of LM. The commonly recognized MFL
ligaments are the Humphry and Wrisberg ligaments,
which travel anterior and posterior to the PCL,
respectively.
 Occasionally the meniscofemoral Humphry ligament
can appear as a large low-signal-intensity structure
within the notch that may resemble a displaced
meniscal fragment.

19. Prominent Humphry ligament (arrow) as it approaches its femoral attachment.
Ligament can be distinguished from displaced meniscal fragment by its course on
sequential sagittal images

20.  Recently, studies have reported that a far lateral
insertion of the MFL onto the posterior horn of the
LM (seen on four or more 3-mm-thick images with a
0.5-mm inter-section gap) should be considered a
probable peripheral longitudinal tear.

21.  The popliteomeniscal fascicles are fibrous bands
covered by synovium that attach the posterior horn
of the lateral meniscus to the joint capsule.
 Most commonly described popliteomeniscal fascicles
are the anteroinferior, posterosuperior, and
posteroinferior.

22. Sagittal T2-weighted MR image obtained depicts the posteroinferior fascicle
(arrow). Note the adjacent MFL (arrowhead)

24.  The oblique meniscomeniscal ligament connects the
anterior horn of one meniscus with the posterior
horn of the contralateral meniscus and is present in
only 1%–4% of knees. When present, it can simulate a
centrally displaced meniscal fragment.

25. ANATOMICAL VARIANTS
 Those who interpret knee MR examinations should
be aware of the MR appearances of normal
meniscal variants that could be confused with
meniscal abnormalities.

26.  Discoid meniscus
 Ring lateral meniscus
 Meniscal flounce
 Meniscal ossicle
 Chondrocalcinosis
 Variation in attachment of anterior horn of MM

27. DISCOID MENISCUS
 Occasionally a meniscus can extends farther onto
the articular surface of the tibia. This variant is called
a discoid meniscus. More common in the lateral
meniscus than in the medial meniscus.
 Body of the meniscus measures 15 mm or more on
a midline coronal image or when three or more
bow-tie shapes are identified on contiguous sagittal
(4-mm-thick) images.

29.  Watanabe classification recognizes three distinct
variants of discoid meniscus:
1. the complete variant
2. the partial variant
3. the Wrisberg variant has a thickened posterior horn,
lacks the normal posterior meniscal attachments.

30. MENISCAL FLOUNCE
 Rippled appearance of the free non-anchored inner
edge of the MM, which can be seen in 0.2%–0.3% of
asymptomatic knees. Typically, this is secondary to
flexion of the knee.
 On coronal images, it may simulate a truncated
meniscus and mimic a radial tear.

32. MENISCAL OSSICLE
 A meniscal ossicle is a rare entity with a predilection
for the posterior horn of the MM. Its cause may be
developmental, degenerative, or posttraumatic.
 On radiographs, the ossicle can be mistaken for a
loose body, while at MR imaging, its increased signal
intensity can mimic a tear.

34. RING LATERAL MENISCUS
 A ring lateral meniscus is a rare meniscal variant in
which the lateral meniscus is in the shape of a
complete.
 Because of the presence of meniscal tissue adjacent
to the notch, those interpreting an MR examination
might misdiagnose this tissue as a displaced meniscal
fragment.

36. CHONDROCALCINOSIS
 Similar to a meniscal ossicle, chondrocalcinosis can
result in increased meniscal signal intensity,
 Its prevalence increases with age and ranges from
5% to 15%. Once again, correlation with
radiographs will aid in reducing the number of false-
positive diagnoses.

37. NORMAL VARIATION IN ANTERIOR
HORN ATTACHMENT OF MM
 The most distinctive normal variant seen in 15%
attachment on the anterior margin of the tibia near
the midline. The meniscus at the midportion of the
medial tibial plateau lies anterior to the tibial margin
misinterpreted as anterior subluxation.

38.  An infrequent finding at the anterior horn of the
medial meniscus adjacent to the root is a ligament
extending from the meniscus to the anterior cruciate
ligament (ACL). This attachment is visualized on MRI
only occasionally; however, when it is thick, it may
appear to be a displaced meniscal fragment

39. MENISCAL TEARS
 The prevalence of meniscal tears increases with age,
and meniscal tears are often associated with and
contribute to degenerative joint disease.
 Tears are more common in the posterior horn of the
menisci, particularly favoring the more constrained
MM. However, in younger patients with an acute
injury, LM tears are more common.

40. CRITERIA FOR DIAGNOSING
MENISCAL TEAR
 Meniscal distortion in the absence of prior surgery
or increased intrasubstance signal intensity
unequivocally contacting the articular surface, seen
on two or more images, fulfilling the “two-slice-
touch” rule, then the PPV for a tear is 94% in the
MM and 96% in the LM, and the imaging findings
should be reported as a meniscal tear.

41.  If these criteria are present on only one image, then
the PPV for a tear is 43% in the MM and 18% in the
LM, and the finding is best reported as a possible
tear.

42. CLASSIFICATION
 When a tear is identified, accurate description of its
morphology and tear pattern is critical for treatment
planning, as longitudinal tears are often amenable
to repair, whereas horizontal and radial tears may
require partial meniscectomy.

43. A commonly used surgical classification of meniscal tears
includes the following types:
• horizontal
• Horizontal
• Longitudinal
• Radial
• bucket handle
• displaced flap
• root
• complex

45. HORIZONTAL TEAR
 Runs parallel to the tibial plateau, involves either
one of the articular surfaces or the central free
edge, and extends toward the periphery, dividing
the meniscus into superior and inferior halves.
 Common, representing 32% of the medial and
lateral meniscal tears.

47.  Often confined to the posterior horn, they may
extend into the body and anterior horn of the
meniscus.
 Patients with horizontal meniscal tears often recall no
specific episode of trauma but report new or
increased knee pain after increased physical activity.
 Usually occur in patients more than 40 years old
without an initiating trauma, they are sometimes
classified as degenerative tears

48. MR APPEARANCE
 Appear on MRI as a horizontally oriented line of
increased intrameniscal signal that extends to the
superior or inferior surface of the meniscus near the
free edge.
 Para meniscal cyst formation is associated with
complete horizontal tears that extend to the
periphery, presumably secondary to direct
communication with the joint fluid.

52. LONGITUDNAL TEAR
 Longitudinal tears run perpendicular to the tibial
plateau and parallel to the long axis of the meniscus
and divide the meniscus into central and peripheral
halves.
 Pure longitudinal tears do not involve the free edge
of the meniscus.

55.  These tears are almost always associated with a
significant knee injury, especially an ACL tear.
 Propensity to involve the peripheral third of the
meniscus and posterior horns.

56. MR APPEARANCE
 They are diagnosed on MRI by the presence of a
vertical line of increased signal intensity contacting
the superior, inferior, or both surfaces of the
meniscus.
 It is sometimes difficult to identify peripheral
longitudinal tears in the posterior horn of the lateral
meniscus because of the complex posterior
attachments of the meniscus. In these cases, the tear
is often more conspicuous on sagittal T2-weighted
images.

58. ADDITIONAL SIGNS FOR
LONGITUDNAL TEAR
 Disruption of the posterosuperior popliteomeniscal
fascicle has a high PPV for tears of the LM posterior
horn and a far lateral attachment of the MFL (>14
mm beyond the lateral border of the PCL) also likely
represents a tear.

59. RADIAL TEAR
 Radial tears are perpendicular to the long axis of the
meniscus. These are high energy tears.
 Radial tears disrupt the meniscal hoop strength,
resulting in a dramatic loss of function and possible
meniscal extrusion

61.  Commonly involve the posterior horn of the MM or
the junction of the anterior horn and body of the LM.

62. MR APPEARANCE
 Various imaging signs can be seen with a radial tear,
including the “truncated triangle,” “cleft,” “marching
cleft,” and “ghost meniscus” signs.
 The following combination of findings is diagnostic:
In one plane: triangle missing the tip and in the
other plane: a disrupted bow tie.

65.  The cleft sign is not specific and can be seen with
both longitudinal and radial tears, depending on the
location of the tear relative to the imaging plane.
 On coronal MR images, if the cleft is within the body,
it is the result of a longitudinal tear. If the cleft is
within the horn, it is the result of a radial tear. The
opposite combination holds true on sagittal MR
images.

66. ROOT TEAR
 A meniscal root tear is a radial tear located at the
meniscal root.
 On coronal MR images, the root should course over
its respective tibial plateau on at least one image.
 On sagittal MR images, if the posterior root of the
MM is not detected just medial to the PCL, a root
tear should be suspected.

68.  Meniscal root tears are often associated with
extrusion of the meniscus beyond the margin of the
tibial plateau. More than 3 mm meniscus extrusion is
often associated with tears involving the meniscal
root.

70.  When there is a complete radial tear, the two
meniscal fragments can be completely
separated. This can result in an empty meniscal space
or empty meniscus sign (arrow).

72. COMPLEX TEAR
 A complex tear includes a combination of radial,
horizontal, and longitudinal components (any two
or all three). Often the meniscus appears
fragmented, with the tear extending in more than
one plane.

74. DISPLACED TEAR
 Displaced tears include free fragments, displaced flap
tears, and bucket-handle tears.
 These tears often manifest with mechanical obstruction
and require surgery.
 It can sometimes be difficult to find the displaced
fragment at arthroscopy; if it is not removed, there is often
persistent knee pain and locking.

75.  Flap tears more frequently in the MM, where in two-
thirds of cases, fragments are displaced posteriorly
(near or posterior to the PCL) in the remaining cases,
fragments course into either the intercondylar notch
or superior recess.
 In the LM, fragments are equally distributed along
the posterior joint line and lateral recess.

78. BUCKET HANDLE TEAR
 A bucket-handle tear is a longitudinal tear with central
migration of the inner “handle” fragment.
 This tear pattern occurs seven times more frequently in the
MM.
 It has at least five different MR imaging signs: an absent bow
tie, a fragment within the intercondylar notch, a double PCL,
a double anterior horn or flipped meniscus, and a
disproportionally small posterior horn.
 A bucket-handle tear of the LM -- a double ACL sign.

81.  Although these signs are sensitive, they are not
specific.
 Absent bow-tie sign, where the innermost bow tie is
not present, can also be seen in a small or pediatric
patient and with a radial tear of the body, macerated
meniscus, or prior partial meniscectomy.
 Mimics of the double PCL sign include a prominent
ligament of Humphry, a meniscomeniscal ligament,
and intercondylar osseous bodies

82. INDIRECT SIGNS
 Secondary or indirect signs of a meniscal tear are
MR imaging findings that can accompany meniscal
tears. These signs can increase the reader’s
diagnostic confidence.
 Have low sensitivity, they have high specificity and
high PPVs for an underlying tear.

83.  Para meniscal cyst
 Meniscal extrusion
 Subchondral marrow edema.

84. CONCLUSION
 MRI is a highly accurate imaging method for diagnosing
meniscal tears.
 MR imaging allows accurate characterization of various
tear patterns, which can be instrumental for patient
counseling and surgical planning.
 To avoid errors in diagnosing meniscal tears, those
interpreting MR examinations of the knee need to be
aware of the attachments of the menisci and the normal
variations in meniscal anatomy that may resemble a
meniscal tear.