MRI KNEE.pptx

JSS Medical College, Mysuru
MR Imaging
Anatomy of the Knee with emphasis on internal
derangements
Presenter
Dr.Vishwanath Patil
PG Resident
Moderator
Dr. Anupama C
Senior Resident

IMAGING PROTOCOLS/TECHNICAL
FACTORS
• The use of a dedicated knee coil is mandatory
for a quality study because it improves the
signal to noise ratio.
• Using a small field of view (FOV) :10 to 14 cm
– greatly improves the spatial resolution and
facilitates optimal assessment of the small
anatomical structures of the knee.
• Matrix of 256 × 256 is usually standard

Patient Positioning
• Supine position with leg in full extension. The knee is placed in 10
to 15° of external rotation to realign the anterior cruciate
ligament parallel with the sagittal imaging plane. This is typically
the position of the knee in the relaxed state.
• Only one knee can be imaged at a time.
• Slice Thickness
– 4mm sections are used for axial, coronal and sagittal images of the
knee.
• When needed, submillimeter resolution can be obtained with
three dimensional Fourier transformation (3D FT) volume
protocols.
• In children, 3 mm slices allow optimal medial to lateral joint
coverage in the sagittal plane and anterior to posterior coverage
in the

KNEE ANATOMY
HINGE TYPE OF JOINT
Three articulating
compartments
• Patello-femoral joint.
• Medial femoro-tibial.
• Lateral femoro-tibial.

KNEE ANATOMY

ANATOMY AND IMAGING FINDING
1. MENISCI
2. CENTRAL STRUCTURES OF KNEE
A. ANTERIOR CRUCIATE LIGAMENT
B. POSTERIOR CRUCIATE LIGAMENT
3. MEDIAL STRUCTURES OF KNEE
4. POSTERO-MEDIAL STRUCTURES OF KNEE
5. POSTERO-LATERAL STRUCTURES OF KNEE
6. POSTERIOR STRUCTURES OF KNEE
7. ANTERIOR STRUCTURES OF KNEE
8. ARTICULAR CARTILAGE

MENISCI
• The menisci are C-shaped fibrocartilaginous
structures situated within the knee joint between
the femoral condyles and the tibial plateau.
• Periphery of the menisci are thick and convex
and
• Attach to the inside of the joint capsule, while
tapering towards the intercondylar notch
• The accuracy of MR imaging of meniscal tears is
greater than 90 percent in most series and the
negative predictive value approaches 100
percent

ANATOMY AND MRI APPEARANCE
• C-shaped structures that are conventionally described as having three
segments
– a. Anterior horn
– b. Body
– c. Posterior horn.
• Each meniscus measures approximately 5 mm in height along its
periphery and tapers to a thin inner edge (a triangular shape in cross
section)
• Surfaces – superior and inferior articular surfaces
• During arthroscopy – Superior articular surface and inferior surface to
some extent visualized. However NON VISUALIZATION of outer
nonarticular capsular surface
• MRI appearance
– Low signal in all MR pulse sequence(fibrocartilage nature)
– Best seen in T1WI PD and GRE

MEDIAL MENISCUS
• Semi-circular 🡪 posterior horn is wider
compared to anterior horn
• More open C-shaped (compared to
lateral meniscus = more circular).
• Normally on MRI anterior horn 🡪 1/3 to
1/2 of Posterior horn (sagittal section).
• Bow-tie shape of medial meniscus 🡪two
most peripheral sagittal slices 🡪 when 3-
4mm slice thickness acquired.
• Attachments:
– Medial femoral condyle and tibial plateau
by coronary ligament (deep fibers of MCL –
meniscofemoral and meniscotibial)
– Attached to joint capsule in peripheral
circumference.
Making it less mobile 🡪 more prone for
injury.

LATERAL MENISCUS
• Tight C-shaped (more circular)
• Anterior horn = posterior horn in width
• Loosely attached to joint capsule;
posterolateral=popliteus tendon courses
through intra-articular tunnel; meniscus has no
attachment to LCL🡪more mobile🡪 less likely to
injure compared to medial meniscus.
• Meniscofemoral ligament(part of coronary
ligament)🡪 From posterior horn🡪 2 bundles 🡪
either side of PCL 🡪 attached to inner margin of
medial femoral condyle:
– Anterior – ligament of Humphry
– Posterior – Ligament of Wrisberg.
– (Either one – 70%; Both – 5%)

MENISCI - VARIANTS
• DISCOID MENISCUS
• Dysplastic meniscus🡪 more of disc than C shaped.
• MC in lateral meniscus (3%)
• Enlarged meniscus
• Asymmetry of anterior and posterior horns
• Sagittal image🡪 4-5mm thickness 🡪 continuous meniscus or bow tie appearance in 3 or more
consecutive slices(normally seen only in 2 sections)
• Coronal 🡪 distance between the free margin and the periphery of the body >1.5cm/ extension of
apex towards or into the intercondylar notch.
• Incidental; But more prone to cystic degeneration 🡪 subsequent tears very likely
• MENISCUS FLOUNCE( BUCKLED MENISCUS)
– MC in medial meniscus
– Sagittal image🡪 The free edge of middle segment of the medial meniscus becomes slacked and folded,
undulating or buckled appearance
– Meniscal tear can mimic similar appearance
• MENISCAL OSSICLE
– Embryonic variant / sequelae to trauma
– Small focus of ossification
– MC in Posterior horn of medial meniscus.
– Asymptomatic; Mechanical pain
– PITFALL: Confused with loose body.

MENISCAL TEAR
• Rotation of femur against fixed tibia during flexion and extension.
• MR imaging criteria for diagnosing a tear
1. Meniscal distortion in the absence of prior surgery or
2. Increased intrasubstance signal intensity unequivocally contacting the articular surface.
(Seen on two or more images, fulfilling the “two-slice-touch” rule)
• MR grading of meniscal tear based on their configuration and relation to articular surface:
• GRADE 1: Non-articular focal or globular intrasubstance increased signal (early mucinous
degeneration) 🡪 also in asymptomatic athletes.
• GRADE 2: Intrasubstance linear increased signal extending to capsular periphery of meniscus;
NON-INVOLVEMENT of articular meniscal surface.
• GRACE 3: Extension into at least one articular surface.
• General Morphology
– Medial meniscus: Anterior horn – 6mm Posterior horn- 12mm
– Lateral meniscus: Anterior and posterior horn : 10mm
• Focal step like configuration and wedge defect (NOTCH sign) 🡪 only sign of some tear.
• If a smaller than normal meniscus is encountered 🡪look for displaced fragment

MR grading of meniscal tear

Horizontal tear
• Runs parallel to tibial
plateau
• Involves either articular
surfaces /central free edge
• Dividing the meniscus into
superior and inferior halves

Horizontal tear

Longitudinal Tear
• Run perpendicular to
the tibial plateau and
parallel to the long axis
of the meniscus
• Divide the meniscus into
central and peripheral
halves
• Doesn't involve free
edge

Longitudinal Tear

Radial Tear
• Runs perpendicular to
both the tibial plateau
and the long axis of the
meniscus
• Transects the
longitudinal collagen
bundles as it extends
from the free edge
toward the periphery
• Involves free edge

Radial Tear

Bucket-Handle Tear
• Longitudinal tear with central migration of the inner “handle” fragment
• MM >> LM
• Signs:
– Absent bow tie,
– Fragment within the intercondylar notch,
– Double PCL,
– Double anterior horn or flipped meniscus, and
– Disproportionally small posterior horn

Bucket-Handle Tear

MR imaging signs of a bucket-
handle tear
• A- absent bow –tie
• B- Fragment within the
interchondylar notch
• C- double PCL
• D- double anterior horn
+ diminutive posterior
horn

MENISCAL IMAGING: CHALLENGES
• Numerous imaging pitfalls and artifacts that may simulate a tear and lead to an erroneous
diagnosis. These are especially common in the posterior horn of the lateral meniscus.
• TRANSVERSE INTERMENISCAL LIGAMENT
– Attachment of the transverse ligament to anterior horn of medial or lateral menisci🡪 misdiagnosis for a
tear( sagittal images)
– Overcome: Follow the ligament in successive images🡪 continuous with the normal ligament and seen
coursing through the infrapatellar fat.(FIG)
• MENISCOFEMORAL LIGAMENT
– Ligament of Humphrey and Wrisberg🡪 attached to the posterior horn of the lateral meniscus🡪 mistaken
for a tear.
• POPLITEUS TENDON
– Junction of posterior horn and body of lateral meniscus, the popliteus tendon usually has small amount
of fluid around the sheath🡪 mistaken for a tear.
• MAGIC ANGLE EFFECT
– Posterior horn of lateral meniscus attached to the posterior intercondylar notch🡪 slightly angled ( 55
degree or the magic angle) between the meniscus and the static magnetic field on short TE🡪 appear as
high SI artefact.
– Solution: use a long TE sequence -> disappearance of the magic angle effect.
• PULSATION ARTEFACT FROM POPLITEAL ARTERY
– Phase artefacts from popliteal artery🡪 misdiagnose as tear in the posterior horn of lateral meniscus.
– avoided by recognizing the alternating lines of increased and decreased signal propagating across the
entire image at that level.

CENTRAL STRUCTURES OF THE
KNEE
• ANTERIOR CRUCIATE LIGAMENT

ANTERIOR CRUCIATE LIGAMENT
• The ACL courses from
the posteromedial
aspect of the lateral
femoral condyle to
insert anterolateral to
the anterior tibial spine.

ANTERIOR CRUCIATE LIGAMENT
• The normal ACL has a fan-shaped
striated appearance on both T1-
weighted and T2-weighted
sequences whereas, in contrast,
the PCL appears homogeneously
hypointense on all sequences.
• Fascicles of ACL divided into 2
longitudinal fibres bundles
• Anteromedial bundle(ABM):
longer and stronger
• Posterolateral bundle:
shorter

ACL INJURY
• Mechanism: External rotation
of femur on a fixed tibia with
valgus force.
• MRI appearance
• An increased signal intensity
within the ACL on proton
density and T2W images
indicates an acute or subacute
injury.
• A cloud like or amorphous
mass of increased signal
intensity may be evident
within the ligament reflecting
edema or hemorrhage.

ACL INJURY
• When the ligament is either
absent (“empty notch sign” in
coronal or discontinuous. An
irregular or wavy contour with
disruption of fibers🡪 suggest a
complete ACL tear.
• An abnormal course of the
ACL can be identified by
Blumensaat’s angle, which is
the angle between the roof of
the intercondylar notch and
the line of the ACL, the apex of
which normally points
posteriorly; in ACL rupture, the
apex points anteriorly.

ACL Injury
• Indirect signs of ACL injury
• i. Buckling (abnormal high arc) of the posterior cruciate
ligament giving rise to a “question mark” configuration.
• ii. Uncovered lateral meniscus sign: A vertical line
drawn tangentially to the most posterior margin of the
lateral tibial plateau intersects any part of the posterior
horn of the lateral meniscus 🡪indicates anterior
displacement of tibia
• III. Anterior tibial subluxation : If the distance between
two parallel lines drawn tangential to the posterior
lateral femoral condyle and posterior lateral tibial
plateau is more than 5 mm it is a sensitive ancillary
sign of complete ACL tear
• iv. Lateral notch sign in which the deep lateral femoral
notch exceeds 2 mm in depth
• v. Bone bruises/contusions in the midportion of the
lateral femoral condyle and posterior portion of the
lateral tibial plateau. 🡪”kissing contusions” 🡪
microfractures that occur when the ACL ruptures.

ACL Injury
• vii. Avulsion fracture of the lateral
tibial rim (Segond fracture) is also
suggestive of ACL tear.
• viii. Joint effusion/hemarthrosis is a
common finding associated with ACL
• ix. A tibial spine avulsion is an
uncommon but specific finding for
ACL injury.

Posterior Cruciate Ligament
• The PCL has a broad origin along
the mid aspect of the medial
femoral condyle and tapers as it
inserts along the posterior mid
tibia approximately 1 cm below
the joint line.

Posterior Cruciate Ligament
• PCL injury: MR findings of
PCL injury are
– anatomic disruption
– Increased signal intensity in
the ligament
– Thickening of the PCL
ligament (7mm or more)
• Grading:
– Grade I : Intraligamentous
edema and hemorrhage and
appears as foci of increased
signal in a ligament with
otherwise intact borders.
– Grade II : Partial tears.
– Grade III : Complete tears.

MEDIAL FEMORO-TIBIAL JOINT
STABILIZERS
• Deep & superficial portions of
medial collateral ligament.
• Medial tendons (sar, gra,
semiten, semimem)
• Deep crural fascia of vastus
medialis.
• Further posteriorly deep
portions of medial collateral
ligament with contributing
fibers of semimembranosus
tendon & synovial sheath form
posterior oblique ligament –
major stabilizer of postero-
medial knee.

MEDIAL FEMORO-TIBIAL JOINT
STABILIZERS
• semimembranosus muscle is
the largest of the
posteromedial muscles .
• semitendinosus tendon can be
seen immediately posterior to
it.
• Smaller sartorius muscle is
seen more medially with the
gracilis tendon interposed.
• The vastus medialis muscle is
draped over the medial
femoral condyle.

MCL Injury
• Twisting injuries cause a large number of MCL
injuries.
• Grade 1 injury : A slight contour irregularity or
thickening of the ligament may be seen but
there is no discontinuity of its fibers.
• Grade 2: Discontinuity of some fibers may be
evident.
• Grade 3: Frank discontinuity of all its fibers.
• Conventional radiograph can predict MCL injury
– Pellegrini–Stieda disease or calcification around the
medial femoral condyle represents chronic partial
or complete tears of the MCL
– The reverse Segond fracture : an avulsion fracture of
medial tibial plateau at the attachment of the deep
fibers of the MCL 🡪 associated with PCL disruption
and peripheral medial meniscal tear.

LATERAL FEMORO-TIBIAL JOINT
STABILIZERS
• ANTEROLATERAL JOINT IS
STABILIZED BY – joint capsule &
ilio-tibial tract.
• POSTERO-LATERAL JOINT IS
STABILIZED BY – arcuate ligament
complex.
• Fibular (lateral) collateral ligament
(FCL),
• Biceps femoris tendon,
• Popliteus muscle and tendon,
• Popliteal fibular and popliteal
meniscal ligaments, oblique
Popliteal, arcuate, and
fabellofibular ligaments, and
• Lateral gastrocnemius muscle.

LATERAL FEMORO-TIBIAL JOINT
STABILIZERS

POSTEROLATERAL CORNER OF THE
KNEE
• MRI: LCL is best visualized in entirety in
the coronal planes
• Low signal intensity structures on all
sequences and nearly uniform in
thickness.
• Contour changes, such as thickening
and irregularity, are more typical of
subacute or old injuries.
• Complete tears with discontinuity and
retraction of the fibers may produce a
ribbon-like deformity of the LCL
• Most complete ruptures involve the
conjoined tendon and may produce a
small avulsion of the styloid process of
the fibular head(marrow edema in the
proximal fibula)

POSTEROLATERAL CORNER OF THE
KNEE
• A direct varus force to the knee
produces injuries to the
posterolateral corner.
• Acute injuries of the popliteus
muscle most commonly involve
the myotendinous junction,
whereas avulsion injuries of
fibular insertion are less
common.
• Complete tears of the
poplitealtendon🡪enlargement of
the muscle belly and the
retracted tendon terminates
abruptly.

POSTERIOR STRUCTURES OF THE
KNEE
• Gastrocnemius, soleus, and
plantaris muscles
• The gastrocnemius: Two
heads from the posterior
surface of the medial and
lateral femoral condyles. The
tendons of the gastrocnemius
along with the soleus tendon
form the Achilles tendon.

POSTERIOR STRUCTURES OF THE
KNEE
• Acute injuries of the proximal
gastrocnemius include interstitial
edema of the myotendinous
junction and surrounding soft
tissues. Occasionally, an
intramuscular hematoma forms a
space occupying mass in the
muscle.
• A complete rupture of the
gastrocnemius head is associated
with retraction of the muscle
belly.

ANTERIOR STRUCTURES OF THE
KNEE
• Includes Quadriceps tendon
,patellar tendon, the medial and
lateral patellar retinacula.
• The medial and lateral patellar
retinacula are extensions of the
vastus medialis and lateralis
respectively and contribute to
passive stabilization of the
patella.

KNEE
• The layers of the quadriceps tendon
can be visualized best in sagittal
plane on MRI as uniform low signal
intensity bands with intervening
higher signal intensity fat separating
each layer.
• Discontinuity of any of the tendinous
layers is consistent with partial tears
often involving the rectus femoris
component.

KNEE
• The patellar tendon also has
homogeneous low signal intensity
appearance except for small
occasional triangular areas of
intermediate signal intensity
directly below the patella and
adjacent to the tibial tuberosity.
• The normal thickness of the tendon
does not exceed 7 mm in its
proximal part. A large collection of
adipose tissue, the infrapatellar fat
pad of Hoffa, rests just posterior to
the patellar tendon. The patellar
tendon ruptures less frequently
than the quadriceps tendon.

KNEE
Acute Patellar Tendon Disruption
• This most commonly occurs near
the patellar attachment and is
best seen on sagittal MR images
as discontinuity of the patellar
ligament with buckling of the
tendon, retraction of the patella,
and fluid signal in the
intervening gap.

MRI KNEE.pptx

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