Meniscal injuries

MRI of Menisci
By
MOHAMED ABDELGHANY ELSHERIF
Resident of Radiology
Sohag University Hospitals

objectives
 Normal Meniscal Anatomy
 Functions of the menisci
 MR techniques
 Different meniscal injures
 Diagnostic pitfalls mimicking meniscal tears
 Imaging of the postoperative meniscus

hoop strength and resisting axial load and preventing meniscal extrusion.

NOTES
 The anterior and posterior roots typically attach to the
central tibial plateau, serving as anchors and
maintaining the normal meniscal position and
biomechanical function.

Normal Meniscal Anatomy
Medial meniscus:
 Both horns are triangular in shape and have
very sharp points.
 The posterior horn is always larger than the
anterior horn ? importance

Medial meniscus:
 The posterior root is immediately anterior to the posterior
cruciate ligament.
If it is missing on the sagittal images>>>there is a meniscal
root tear.
 The anterior horn has an insertion on the tibia and a second
portion that travels from medial to lateral to connect to the
anterior horn of the lateral meniscus (anterior
intermeniscal or transverse ligament)>> misdiagnosed
as oblique meniscal tear
 PHMM firmly attached to capsule
? Importance
 In 2% of the population, an anomalous insertion of the MM
anterior root parallels the ACL and can be mistaken for a tear
 MM anterior root can occasionally insert along the anterior
margin of the tibia and mimic pathologic subluxation

LEFT: normal medial meniscal posterior root immediately anterior to the
posterior cruciate ligament. RIGHT: missing posterior root due to
meniscal root tear.
Medial meniscus

Lateral meniscus
 On sagittal images the posterior horn is higher in position than the anterior horn.
 Both horns are about the same size but AHLM may be thin or hypo plastic.
 The intimate association between the anterior root of the LM and the ACL
insertion site commonly results in a striated or comb-like appearance at MR
imaging
NormalMeniscalAnatomy

Lateral meniscus
 The lateral meniscus posteriorly comes up high
over the tibial spine to insert near the posterior
cruciate ligament. This upward position of the
posterior horn may be the reason for the higher
signal intensity of the posterior horn in all
planes due to magic angle effect.

 Normal MR imaging
appearance of the menisci.
 (a) Sagittal PD-weighted MR
images show the typical bow-
tie configuration of the
meniscal body (left) and the
opposing triangles of the horns
(center and right). Th posterior
horn of the MM (arrow) is
larger than the anterior horn,
whereas the horns of the LM are
similar in size and shape.
• (b) Coronal PD-weighted MR
images demonstrate the
triangular morphology of the
meniscal body (left) and the
elongated wedge shape of the
posterior horn (right), which
is continuous with the
crescentic posterior
meniscal root.

O The inner 2/3 of the
menisci are avascular
(without blood supply)
O The remaining outer 1/3 is
vascular (with blood
supply)
Importance ???
*Spontaneous healing of peripheral
tears
* Increased intrameniscal signal
intensity seen at imaging of children

Functions of the menisci
O Lubrication and
nutrition of the joint
O Shock absorbers
O Distribute weight
throughout the knee
O Smoother motions
between the femur
and tibia

MR techniques
MRI is modality of choice for mm sensitivity 95% $specificity 81% for LM sensitivity 85% $specificity 93%
 Plane;
 Sagittal plain (mainly) but meniscal tears are also often detectable in coronal plane
 Although most tears are diagnosed on sagittal images, coronal images are important for
confirming and accurately characterizing various tear patterns. Small radial tears,
horizontal tears of the body, and bucket-handle tears may be difficult to reliably detect
on sagittal images because of volume averaging; these tears may be better depicted on
coronal images In addition, axial images may be helpful for detection of small radial
tears, displaced tears, and peripheral tears of the LM posterior horn
 Sequence;
- PD FSE
- PD fat suppressed CSE >designed for menisci , also helpful in cartilage
Note **FSE introduce blur though CSE take longer to acquire they are the most
accurate sequences for menisci (rollover for PD FSE vs PD fat sat CSE )
- T1 fat suppressed post arthrogram is most beneficial for evaluation
of post-operative menisci. Intra-articular gadolinium helps differentiate between
post-operative high signal that can be seen on PD sequences versus a retear of the
meniscus. The gadolinium will enter a retear in the meniscus. The sequence help
in evaluation of cartilage and ACL reconstructions

Causes
-knee twisting or turning quickly
-lifting something heavy or play sport
-AS you get older ,your meniscus gets worn >> make tear more easily
 What are the symptoms?
There are three types of meniscus tears. Each has its own set of symptoms.
 A minor tear, you may have slight pain and swelling. This usually goes away in 2 or 3 weeks.
 A moderate tear can cause pain at the side or center of your knee. Swelling slowly gets worse
over 2 or 3 days. This may make your knee feel stiff and limit how you can bend your knee, but
walking is usually possible. You might feel a sharp pain when you twist your knee or squat.
These symptoms may go away in 1 or 2 weeks but can come back if you twist or overuse your
knee. The pain may come and go for years if the tear isn't treated.
 In severe tears, pieces of the torn meniscus can move into the joint space. This can make your
knee catch, pop, or lock. You may not be able to straighten it. Your knee may feel "wobbly" or
give way without warning. It may swell and become stiff right after the injury or within 2 or 3
days.
 How is it treated?
How your doctor treats your meniscus tear depends on several things, such as the type of tear, where it is, and how
serious it is. Your age and how active you are may also affect your treatment choices.
-Treatment may include:
 Rest, ice, wrapping the knee with an elastic bandage, and propping up the leg on pillows.
 Physical therapy.
 Surgery to repair the meniscus.
 Surgery to remove part of the meniscus

Meniscal degenerations &Tears
Criteria for tears
 The two most important criteria for meniscal tears are:
*Abnormal shape of the meniscus without prior operation
*High signal intensity unequivocally contacting the articular
surface on PD images
 If these criteria are seen on two or more images, fulfilling the
“two-slice-touch” rule a meniscal tear should be reported
 If these criteria are present on only one image ,the finding is
best reported as a possible tear
Criteria for degenerations
*Abnormal signal intensity (intermediate) not reach articular
surface
*Normal meniscal morphology

Cleavage type
Blunt end ( sagittal) coronal
Ghost M sign
DD
Operative ,
degeneration
, tear

Fraying is defined as surface irregularity along the meniscal free edge without
a discrete tear

Signs of
meniscal degeneration &tear
Abnormal signal
Morphological
Changes (tear)
Grade I
Grade II
Grade III (tear)
Abnormal size
Blunting of
free edge
Displacement of
meniscal fragment
Interrupted
appearance

Normal meniscus
Small meniscus
Truncated free edge
Displaced meniscal
fragment

Types of meniscal tears according to
plane of cleavage
Meniscal
tears
Vertical
(traumatic)
Horizontal
(degenerative) if
traumatic +/- cyst
Longitudinal
Radial (root)
at free edge

Displaced
meniscal tears
Vertical
Horizontal displaced
tear (Flap tear)
Displaced
Longitudinal tear
(Bucket handle tear)
Displaced
Radial tear
(Parrot beak tear)
Types of displaced meniscal tears according
to the original plane of cleavage

Basic shapes: Longitudinal, Horizontal and Radial
Displaced tears Bucket handle, Horizontal Flap tear and Parrot beak.

Horizontal Tear
 Is parallel to the tibial plateau involves
either one of the articular surfaces or the
central free edge, and divide the meniscus
into upper and lower segments.

Horizontal tear with parameniscal cyst

Longitudinal vertical tear
 Is perpendicular to the tibial plateau & parallel to the long axis
of the meniscus.
 Unlike horizontal or radial tears, pure longitudinal tears do not
involve the free edge of the meniscus.

Longitudinal vertical tear
occur in younger patients after significant knee trauma and involve the peripheral
third of the meniscus (red zone )and posterior horns

B )Axial fluid-sensitive
reformatted MR image
shows a peripheral
longitudinal tear involving
the posterior body and
posterior horn that extends
into the posterior
root (arrows)

Radial tear
 is perpendicular to the tibial plateau & perpendicular to the long axis of the meniscus.
 You have to combine the findings on sagittal and coronal images to make the diagnosis. (In one
plane: triangle missing the tip and in the other plane: a disrupted bow tie & Sometimes the only sign
is a disrupted bow tie in small radial tears).
 disrupt the meniscal hoop strength resulting in a dramatic loss of function and possible meniscal
extrusion
 Various imaging signs can be seen with a radial tear, including the “truncated triangle,” “cleft,”
“marching cleft,” and “ghost or empty or absent meniscus” signs. These variable appearances
depend on the tear location (body or horn ) relative to the imaging plane and either partial
thickness or full thickness tear
 Radial tears commonly involve the posterior horn of the MM or the junction of the anterior horn and
body of the LM

 Expected MR imaging appearance of a radial tear. Three-dimensional
model (center) shows two radial tears: a partial-thickness tear of the
body (black arrow) and a full-thickness tear of the anterior horn (white
arrow). Dashed lines = orientation of imaging planes. Diagrams on the
left and right show
 The expected MR imaging appearance of a radial tear, which varies
depending on whether the imaging sequence is performed orthogonal (1
and 3) or in plane (2 and 4) to the orientation of the tear. If the image is
obtained perpendicular to the tear (1 and 3), a cleft will be identified;
however, if the image is obtained parallel to the tear (2 and 4), the
meniscus will appear truncated or absent. Radial tears involve the free
edge of the meniscus, which distinguishes them from longitudinal tears.

MR imaging signs of a radial tear. Sagittal PD-weighted MR images demonstrate the
cleft sign (arrowhead in a), the truncated triangle sign of a partial-thickness tear
(arrowhead in b), and the ghost meniscus sign associated with a full-thickness tear
(arrow in c). Each tear involves the free edge of the meniscus.

Marching cleft sign of a radial tear.
(a) Sagittal PD-weighted contiguous
MR images show a vertically
oriented cleft (arrows) “marching”
from the free edge into
the substance of the meniscus
at the junction of the body and
anterior horn.
(b) Axial fluid sensitive
reconstructed MR image shows the
oblique course of a radial tear
(arrow) with respect to the sagittal
plane, which accounts for the MR
imaging appearance of a tear
propagating out of plane

Radial tear
For example, a tear through the meniscal body would appear as a cleft on sagittal MR
images and as a truncated or ghost meniscus on coronal MR images. Conversely, a tear
through the horn would appear as a truncated or ghost meniscus on sagittal MR
images (and as a cleft on coronal MR images

Teaching point
 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.

Full thickness body radial tear

If you image a complete radial tear directly along the length of
the tear you will see an absent or empty meniscus.
These complete radial tears open up and give the impression
that there is a part missing. However you will not find a
displaced meniscal fragment. It is simply separation of the
meniscal parts

Root tear
Complete root tears have a high
association with meniscal extrusion
particularly when the tear occurs in the MM.
A radial-type tear
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 anterior
to the PCL, a root tear should be suspected.
In addition, when an ACL tear is present,
there is an increased incidence of lateral
root tears . Acute root tears without
significant underlying degenerative
changes are often promptly repaired because
the surrounding rich synovial blood supply
facilitates postoperative healing

Meniscal root tear
Normally when you image the posterior cruciate ligament on sagittal
images you should see a considerable portion of the posterior horn of the
meniscus on that image or the image adjacent to it.
If this is not the case it is an absent or empty meniscus-sign, indicating a
radial tear

 Coronal PD
weighted
(a) and axial fluid
sensitive
reconstructed
(b)MR images show
a complete posterior
root tear (arrow).
(c) Arthroscopic
image shows a torn
posterior root.

Indirect secondary signs
 Meniscal extrusion
 Meniscal cyst
 Linear subchondral bone marrow edema

Meniscal extrusion
 Extrusion is present when the peripheral margin of the meniscus
extends 3 mm or more beyond the edge of the tibial plateau
 There is a close association between meniscal extrusion and root
tears
 However, meniscal extrusion can also be seen with complex tears,
large radial tears, and severe meniscal degeneration

Meniscal cyst
**There are 3 criteria for the diagnosis of a meniscal cyst:
 Horizontal tear.
 Fluid accumulation with bright signal on T2.
 Flat lining against the periphery of the meniscus
**Pathology
The synovial fluid runs peripherally through the horizontal tear and
accumulates within the meniscus and finally result in a cyst.
The connection with the joint space is often lost, so they will not fill with
contrast on MR-arthrography.The synovial fluid is absorbed and is
replaced by a gelatinous substance.
**The diagnosis of a meniscal cyst is important to the surgeon
because it takes one operation on the outside of the knee to remove
the cyst and another operation on the inside for the meniscus

Horizontal tear with a meniscal cyst

Subchondral Marrow Edema
 Linear subchondral bone marrow edema, in
contrast to the more nonspecific edema often seen
with degenerative changes, is defined as superficial
edema that is adjacent to the meniscal attachment
site, parallels the articular surface, and is less than 5
mm deep (Indirect sign of meniscal tear)
extrusion edema

Complex tears
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

Types of displaced meniscal fragment according the
direction of displaced fragment
Displaced
mensical fragment
Intercondylar
notch
Mensico-capsular
recesses

Flap tear
occur six to seven times 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

 (a) Coronal T2-weighted MR
image shows a flipped
fragment within the
intercondylar notch (arrow)
from a complex tear of the
MM.
 (b) Sagittal PD-weighted MR
image shows a large flipped
fragment (arrow) in the
popliteal recess from a torn
LM.
 (c) Coronal PD-weighted MR
image (left) and
corresponding
anteroposterior radiograph
(right) show a laterally
displaced meniscal fragment
(arrowheads) extending into
the superior recess, with
central areas of
Chondrocalcinosis.
 (d) Arthroscopic image shows
a meniscal flap.

Bucket handle tear
MR imaging signs:
 Absent bow tie
 A fragment within
the intercondylar
notch
 Double PCL
 Double anterior horn
or flipped meniscus
 Small posterior horn

Bucket handle tear
MR imaging signs of a bucket-handle tear.
(a) Sagittal PD weighted MR image shows the
absent bow-tie sign, with non visualization of
the meniscal body (arrows).
(b) Sagittal PD-weighted MR image shows
the fragment within the intercondylar notch
sign, with a centrally displaced meniscal
fragment (arrow) eccentric to the PCL. This
finding is commonly seen with lateral tears
because an intact ACL impedes the fragment
from reaching the level of the PCL.
(c) Sagittal PD-weighted MR image shows the
double PCL sign, with a displaced fragment from
the MM anterior and parallel to the PCL (arrow).
(d) Sagittal PD-weighted MR image shows the
double anterior horn sign, with a meniscal
fragment (white arrow) posterior to and
displacing the native anterior horn (black arrow)
and a markedly diminutive posterior horn
(arrowhead).

Normal bow tie appearnace of the
meniscal body

Flipped variant of bucket handle tear
More common in lateral meniscus tears

Double anterior horn sign
Flipped bucket handle tears

Parrot beak tear (radial oblique tear)

Diagnostic pitfalls mimicking
meniscal tears
Normal anatomic structures or anatomic variants
that show similar MR SI to the meniscus are
common mimickers of meniscal pathology

Normal anatomic structures that can mimic a tear
 Anterior meniscal(transverse OR geniculate )
ligament.
 Menisco femoral ligaments (ligament of Humphry anterior and the
ligament of Wrisberg posterior )
 Oblique meniscal ligament (The medial and lateral oblique
menisco-meniscal ligaments)
 Popliteus tendon (popliteomeniscal fascicles)
 ACL insertion(A speckled appearance ).
 Semimembranosus tendon
 The lateral inferior genicular artery

Anterior intermeniscal (transverse) ligament
 Attach anterior horns of both menisci to each other

 The anterior
transverse ligament
is clearly
demonstrated on
coronal PD-W fat sat
(a) and T1-W images
(b) and on axial PD-
W fat sat (c) and T1-W
images (d) as it
courses from the
anterior margin of
lateral meniscus to
the anterior horn of
medial meniscus

ON sagittal views a linear band of increased signal intensity (arrowhead) is noticed on
a sagittal PD-W fat sat image (j), between the anterior horn of lateral meniscus and
the anterior transverse ligament (arrow), simulating an oblique meniscal tear. The
course of the ligament is clearly demonstrated on adjacent sagittal PD-W fat sat
images (ej). Osgood-Schlatter disease is also present with patellar tendon thickening,
deep infrapatellar bursitis and tibial tubercle fragmentation.

Meniscofemoral ligament
 Attach PHLM to medial femoral condyle
 The ligament is composed of 2 separate branches, the ligament of
Humphry and the ligament of Wrisberg
 assist the PCL and help control the mobility of the posterior horn of the
LM during knee flexion and extension

The anterior meniscofemoral ligament (Humphry )
A linear band of increased signal intensity (arrowheads) is noticed on
sagittal PDW fat sat images (e, f), between the posterior horn of lateral
meniscus and the ligament of Humphry, simulating a vertical meniscal tear.
The anterior meniscofemoral ligament (arrows) is clearly demonstrated on
adjacent sagittal PD-W fat sat images (a-f).

The anterior meniscofemoral ligament (arrows) is depicted on adjacent
coronal PD-W fat sat images (g, h) as it courses from the medial aspect of
medial femoral condyle to the medial aspect of the posterior horn of
lateral meniscus. A horizontal tear of the posterior horn of medial
meniscus (arrowheads) is also noticed.

The ligament of Humphry (arrows) is demonstrated on adjacent axial
PD-W fat sat images (i-l) as it courses from the medial aspect of medial
femoral condyle to the medial aspect of the posterior horn of lateral
meniscus.

The ligament of Wrisberg (arrows) is depicted on adjacent coronal PD-W
fat sat images (f, g) as it courses from the medial aspect of medial
femoral condyle to the medial aspect of the posterior horn of lateral
meniscus. A horizontal tear of the posterior horn of medial meniscus
(arrowheads) is also noticed.

A linear band of increased signal intensity (arrowhead) is noticed on a sagittal PD-W fat
sat image (e), between the posterior horn of lateral meniscus and the ligament of
Wrisberg, simulating a vertical meniscal tear. The posterior meniscofemoral ligament
(arrows) is clearly demonstrated on adjacent sagittal PD-W fat sat images (ae).

Popliteal tendon
O Runs behind PHLM
O may also be mistaken for a vertical or slightly diagonal meniscal
tear of PHLM

.
Fluid within the bursa (arrowhead) appears as high-signal intensity on a sagittal
PD-W fat sat image (e) and gives the appearance of a vertical or slightly diagonal
tear in the posterior horn of lateral meniscus. The popliteus tendon and bursa
(arrows) are clearly demonstrated on adjacent sagittal PD-W fat sat images (a-e).

Fluid within the bursa (arrowhead) appears as high-signal intensity on a coronal
PD-W fat sat image (f) and resembles a vertical or slightly diagonal tear in the
posterior horn of lateral meniscus. The popliteus tendon and bursa (arrows) are
demonstrated on adjacent coronal PD-W fat sat images (f, g).

Oblique intermeniscal ligament
 Extend obliquely from the anterior horn of one meniscus to
the posterior horn of the> e.g Attach from AHMM to PHLM
 The medial and lateral oblique menisco-meniscal ligaments
have a reported incidence of 1% to 4% and are an uncommon
source of diagnostic difficulty

The medial oblique menisco-meniscal ligaments.
Sagittal T1-W (a) and PD-W fat sat images (b) through the intercondylar notch at
the level of PCL demonstrate the medial oblique menisco-meniscal ligament as a
thin linear structure of low signal intensity (arrows) mimicking a displaced
meniscal fragment. A Baker's cyst is also noticed (arrowheads). Coronal PD-W fat
sat image (c) shows the ligament as it passes through the intercondylar notch.

Bucket-handle meniscal tear of medial meniscus. The thin linear structure of low
signal intensity (arrow) which courses under the PCL (arrowheads) on a sagittal T2-
W image (a) represents a displaced meniscal fragment ("double PCL sign"). The
meniscal fragment (arrow) is also demonstrated as it passes through the
intercondylar notch under the PCL (arrowheads) on a coronal PD-W fat sat image
(b).

Oblique intermeniscal ligament
Versus
Bucket handle tear

The medial oblique menisco-meniscal ligament

Semimembranosis tendon
Runs behind PHMM

The lateral inferior genicular artery
 Arises from the popliteal artery at the level of the
tibiofemoral joint and courses laterally to the
anterior aspect of the knee where it and other
arteries compose the genicular anastomosis.
 Unlike the superior genicular arteries and the
inferior medial genicular artery, the lateral
inferior genicular artery is closely applied to the
meniscus as it wraps around the knee, lying in a
periarticular fat pad between the meniscus and
lateral collateral ligament (LCL).

Adjacent sagittal T1-W images through the lateral meniscus (a-d) demonstrate
the course of the lateral inferior genicular artery (arrows). A narrow separation
(arrowhead) between the anterior horn of lateral meniscus and the lateral
inferior genicular artery (c) can sometimes be mistaken for a meniscal tear.

Anatomic variants that can mimic a tear
 Meniscal root ligaments
Medial meniscus:
• The posterior root is immediately anterior to the posterior cruciate ligament.
If it is missing on the sagittal images>>>there is a meniscal root tear.
• In 2% of the population, an anomalous insertion of the MM anterior root
parallels the ACL and can be mistaken for a tear
• MM anterior root can occasionally insert along the anterior margin of the tibia
and mimic pathologic subluxation
Lateral meniscus
The intimate association between the anterior root of the LM and the ACL insertion
site commonly results in a striated or comb-like appearance at MR imaging
 Discoid Meniscus
 Meniscal Flounce
 Meniscal Ossicle (Meniscal ossification )
 Chondrocalcinosis

Adjacent crossing fibers of the ACL
 May give the anterior horn of lateral meniscus speckled appearance.
 A speckled appearance of the anterior horn of lateral meniscus is a frequent finding
that has been explained by fibers of the anterior cruciate ligament inserting into the
meniscus.
 Seen on one or two of the most medial sagittal images.
 The appearance can be mistaken for a torn lateral meniscus.

A speckled appearance (white arrows) of the anterior horn of lateral
meniscus on adjacent sagittal PD-W fat sat images (a, b), which is caused
by the insertion of the fibers of anterior cruciate ligament (black arrow)
into the meniscus (c). The finding can easily be mistaken for a torn
lateral meniscus.

 Represents an enlarged meniscus with further central extension onto the
tibial articular surface.
 It is seen in 1%–5% of knees and is 10–20 times more common in the LM
than in the MM.
 The Watanabe classification recognizes three distinct variants of discoid
meniscus: (a) The complete variant has a block shaped meniscus that covers the
entire tibial plateau
(b) The partial variant has a meniscus that covers 80% or less of the tibial plateau
(c) The Wrisberg variant has a thickened posterior horn , lacks the normal
posterior meniscal attachments , and can cause snapping knee syndrome
 The modified Watanabe classification includes a ring-shaped meniscus with
connection between the roots. This variant can mimic a medially displaced
meniscal fragment
 Discoid meniscus is diagnosed when the body of the meniscus measures 15
mm or more on a midline coronal image or when three or more bowtie shapes
are identified on contiguous sagittal (4-mm-thick) images.
 No symptoms = no TTT
 If symptomatic must be treated (common cause of knee pain in children thus
diagnosis of tear is very difficult Why ? )

Diagnosis of tear in discoid meniscus
 Tears are more common with the complete discoid meniscus variant and
often display horizontal or longitudinal tear patterns
 MR imaging has widely variable sensitivity and specificity for detection of
tears within a discoid meniscus because of the increased meniscal vascularity
and diffuse intrameniscal signal intensity (child).
 Therefore, diagnosis of a tear relies more heavily on morphologic distortion
than on abnormal signal intensity. However, an area of linear increased signal
intensity that is seen to unequivocally contact the articular surface on two or
more images is almost always associated with a meniscal tear.
 In contrast, diffuse intrameniscal signal intensity extending to the articular
surface has been shown to have a poor PPV (57%–78%) .Currently we report
the latter finding as a possible tear.

Coronal fat-suppressed PD weighted MR image through the
body of the menisci shows a discoid LM (arrow) that
measures 19 mm (normally <15 mm).

Meniscal Flounce
 Meniscal flounce is a rippled appearance of the free non anchored inner
edge of the MM, whichcan be seen in 0.2%–0.3% of asymptomatic knees .
 Typically, this is secondary to flexion of the knee and redundancy of the free
edge of the MM. This distortion does not indicate a tear; however, on coronal
images, it may simulate a truncated meniscus and mimic a radial tear.
 At arthroscopy, the “flounce” sign is more common because of knee
positioning and anesthetic relaxation and usually signifies the absence of a
tear

 Meniscal Ossicle
 A meniscal ossicle is a rare entity , more common at PHMM.
 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 and a review of the
patient’s radiographs can prevent false-positive diagnosis of a tear.
 Frequently asymptomatic and discovered incidentally but if give Symptoms
result from mass effect or from an associated tear, which can be treated with
arthroscopic resection.

 Chondrocalcinosis
 is defined as a radiographically visible calcification in the cartilage of a
joint. It can occur in the hyaline articular cartilage lining the articular
surface or in the fibrocartilage of a meniscus.
 Although it can occur from many types of calcium crystals, the most
commonly seen is from calcium pyrophosphate dihydrate crystal
deposition in pseudogout, which is also known as calcium
pyrophosphate dihydrate deposition disease.
 When MR imaging is performed on a meniscus with chondrocalcinosis,
the T1-weighted or PD-weighted sequence shows high signal, which can
be mistaken for a meniscal tear. Differentiating a meniscal tear from
the high signal of chondrocalcinosis can be difficult, if not impossible.
 Most meniscal tears have a more linear appearance than the globular
high signal seen in chondrocalcinosis. Comparison with a conventional
radiograph of the knee will help avoid this pitfall. However,
chondrocalcinosis can also obscure a tear and result in a false-negative
report.

Chondrocalcinosis in medial
meniscus. Radiograph of the knee
(a) reveals meniscal calcifications
in the posterior horn of the
meniscus (arrow). Coronal PD-W
(b) and sagittal PD-W images (c,
d) show marked high signal
throughout the posterior horn of
medial meniscus (arrows) that
resemble a tear. No meniscal tear
at the arthrography.
Chondrocalcinosis in lateral
meniscus. Anteroposterior knee
radiograph (a) shows meniscal
calcifications in lateral meniscus
(arrow). Sagittal PD-W image (b)
shows high signal intensity both in
the anterior and posterior horn of
lateral meniscus with extension to
inferior articular surface
(arrowheads), interpreted as
meniscal tears. No meniscal tear
was found on arthroscopy

Imaging of the postoperative meniscus.

Imaging of the postoperative meniscus.
(A) Total meniscectomy displayed as
complete absence of the meniscus.
(B) Partial meniscectomy shown as a
diminutive size of the meniscus with a well-
circumscribed contour.
(C) MR arthrogram image in a partial
meniscectomy is characterized by a linear
line in the substance of the meniscus
indicating contrast intrusion into the tear.
(D) Surgical repair of a meniscus tear
demonstrates a small cleft at the site of
the tear but is less than 10% of the meniscus
thickness. There is lack of contrast intrusion
into the sutured portion indicating complete
healing.
(E) Incomplete healing in a surgically
repaired meniscus characterized by a
contrast-filled cleft that involves greater than
10% but less than 50% of the meniscus
thickness.
(F) Failed surgical repair of the meniscus
demonstrated by a large contrast-filled cleft
involving greater than 50% of the meniscus
thickness.

Take home massage
 Magnetic resonance (MR) imaging is the modality of choice for
detecting meniscal injuries and planning subsequent treatment.
 Familiarity with the normal anatomy, common anatomic variants ,
anatomic structures , and indirect secondary signs of meniscal tears
can help reduce interpretation errors
 When a meniscal tear is identified, accurate description and
classification of the tear pattern can guide the referring clinician in
patient education and surgical planning. For example, longitudinal
tears are often amenable to repair, whereas horizontal and radial
tears may require partial meniscectomy.
 Tear patterns include horizontal, longitudinal, radial, root, complex,
displaced, and bucket-handle tears.
 Occasionally, meniscal tears can be difficult to detect at imaging;
however, secondary indirect signs, such as a parameniscal cyst,
meniscal extrusion, or linear subchondral bone marrow edema,
should increase the radiologist’s suspicion for an underlying tear
 Meniscal tears can be treated with conservative therapy, surgical
repair, or partial or complete meniscectomy.

Meniscal injuries

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