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MRI of the Knee:
Part 2 - menisci
Mark Anderson, M.D. University of Virginia Health System
Learning Objectives • At the end of the presentation, each participant should be able to:
• describe the normal anatomy of the menisci and the MR imaging appearance of each
• discuss the most common types of meniscal tears and list which are most important to the surgeon.
• recognize at least five imaging pitfalls that may mimic a meniscal tear on MR images.
Lecture Outline
• Normal anatomy / variants • Meniscal tears
– radial / longitudinal / parrot beak / horizontal – displaced
• Diagnostic pitfalls
Menisci
• Fibrocartilage • Medial/Lateral • Functions:
Joint congruity Shock absorption Load transmission
MED LAT
Menisci
• Segments
– anterior horn
– body
– posterior horn
MED LAT
A
B
P
B
P
A
White Zone Red Zone
Medial Meniscus
• Larger “C”
• Post horn > ant horn
• Attached more tightly to the capsule
• Covers ½ contact surface of tibial plateau
Lateral Meniscus
• Tighter “C”
• Post horn = ant horn
• Attached more loosely to the capsule
• Popliteus tendon (fascicles)
• Covers ¾ contact surface of tibial plateau
Meniscus: anatomy and function
• Collagen bundles • longitudinal • radial (“tie fibers”)
MED LAT
Bullough, JBJS, 1970
Meniscus: anatomy and function
• Cartilage protection – shock absorption – load distribution
• “Hoop stresses”
• Roots – anterior/posterior – anchors
Menisci: Attachments
• Tibia • Capsule • Ligaments
Meniscal Attachments: medial
• Tibia: “roots”
– Anterior • largest footprint • anterior tibial rim
– Posterior • Medial and slightly ant to distal PCL
PCL
Meniscal Attachments: medial
• Capsule – firmly attached
Meniscal Attachments: medial
• Capsule – firmly attached
• Deep fibers of MCL
– femoral limb • to bone or superficial MCL
– tibial limb • aka “coronary ligament
Meniscal Attachments: lateral
• Roots
– Anterior • adjacent to ACL • fibers intermingle
– Posterior • post to post-lat bundle of ACL
Meniscal Attachments: lateral
• Lateral attachments
– capsule
– popliteus hiatus • fascicles • anterior inferior • posterior superior • (posterior inferior)
LM
Meniscal Attachments
• Meniscofemoral ligs
– PHLM – MFC
– Wrisberg (post)
– Humphrey (ant)
LM PCL
Meniscal Attachments
• Meniscofemoral ligs
– PHLM – MFC
– Wrisberg (post)
– Humphrey (ant)
• Anteromedial M-F lig – Soejima, Arthroscopy 2003 – Coulier, JBR-BTR 2008 – ant horn medial meniscus – anterior notch
Menisci: attachments
• Transverse ligament – ant horn – ant horn
Menisci: variants
• Discoid – enlarged meniscus – embryologic, congenital? – lateral > medial – prone to tear – types
• complete • incomplete • Wrisberg variant
- Sagittal: “too many bow ties”
Prone to tear
Meniscus: meniscal ossicle
• Posterior horn MM – cancellous bone
• Uncertain etiology – vestigial? – post-traumatic?
• root avulsion - PHMM
• May be symptomatic
• Imaging – “loose body”
Gradient Echo
Meniscal Tear: MRI
Morphology Signal intensity
Abnormal
Meniscal Tear: MRI
• Signal Intensity
Contact with articular surface (not capsular surface alone)
Globular Linear
TEAR
Meniscal Tear: MRI
• Morphology – shape
• blunted, truncated – size
Mensical Tears: types
VERTICAL
HORIZONTAL
Radial
Longitudinal
Meniscal Tear: radial
• Vertical
• Perpendicular to long axis
– across longitudinal bundles
• Unrepairable?
– always involve the white zone
Meniscal Tear: radial
Meniscal Tear: radial
Medial Meniscus: posterior root
• Attaches next to PCL – tear releases posterior anchor
• Avulsion / tear – “quartet” of findings
– root tear – meniscal extrusion (> 3mm)
– cartilage loss – insufficiency fracture (aka SONK)
Medial Meniscus: posterior root
• Repair? – Depends on:
• patient’s age • acute vs. chronic • articular cartilage
• “Pull out” repair
PCL
College football player with hyperextension injury
Allaire R, JBJS(Am) 2008;90:1922-1931
Meniscal Tear: longitudinal
• Longitudinal – Vertical – Along axis of meniscus
– Bucket handle • displaced fragment • medial meniscus • locking
Longitudinal Tear: peripheral
• Vertical longitudinal
• Confined to outer 1/3
– “peripheral” – vascularized
– potential for healing / repair
• < 1 cm in length = conservative Rx • > 1 cm = repair
• Often seen with ACL tears
• In outer 1/3 in all planes
• Axial images may help
• May heal prior to surgery
Longitudinal Tear: peripheral
32 yr old male tore ACL while playing soccer
Stable, “no tear” at time of arthroscopy
32 yr old male tore ACL while playing soccer
Peripheral Tear
vs.
Meniscocapsular Separation
Periph Tear vs. MC Separation
Meniscal Tear: parrot beak
radial + longitudinal oblique to long axis
• Combination
• Meniscal Flap
*
Meniscal Tear: horizontal
• Often degenerative
• Older patients
• May be asymptomatic
• Often degenerative
• Older patients
• May be asymptomatic
• Parameniscal cysts
- often w/ horizontal tears - fluid extrudes through tear – trapped at M-C junction – cyst may recur if tear is not addressed
Meniscal Tear: horizontal
33M marathon runner
Small meniscus? Find the fragment
Bucket Handle Tear
• Bucket handle
• Longitudinal tear – displaced flap – notch – medial >>> lateral
• Coronal – central fragment
Displaced Tears
Sagittal: “Double PCL”
P
• Double bucket-handle tear – second tear may be missed
Bucket Handle Tear: variant
• Hemi-bucket-handle tear
– fragment displaced into notch
– not vertical peripheral
– horizontal undersurface
– less amenable to repair
Engstom, Skeletal Radiol, 2012
Bucket Handle Tear: variant
Horizontal tear: displaced fragment
1 2
1
2 1
2
Flipped posterior horn fragment
“double anterior horn” sign
Displaced Meniscal Tears
Displaced Meniscal Tears: importance
• Bucket handle tear
• Flipped ant/post horn
– detected early - repair
– detected late – plastic deformity
• Horizontal flap tear – fragment may be missed at arthroscopy
T
Meniscal Tear: Pitfalls
• Artifacts – Patient motion – Phase artifact (artery) – Magic Angle – Gas/hemosiderin – Chondrocalcinosis
PD
Meniscal Tear: Pitfalls
• Anatomy – Transverse ligament – Meniscofemoral liagments – Oblique meniscomeniscal lig – Lateral inf geniculate artery – Popliteus tendon – Edge artifact
Meniscal Tear: mimic
Transverse ligament
Meniscal Tear: mimic
Meniscofemoral ligament
?
If signal extends > 4 slices lateral to the PCL – think tear Park LS, Skeletal Radiol 2007
Meniscal Tear: mimic
• Oblique meniscomeniscal ligament – ant horn one meniscus – post horn of the other – courses between cruciates – may simulate BHT
Sanders TG, Radiology 1999
Displaced fragment?
Meniscal Tear: mimic
?
Posterior root pseudotear
PCL
Meniscal Tear: mimic
• Lat inf geniculate vessels – parallel lateral meniscus – along its outer margin – volume avg artifact – may mimic obl meniscal tear
• Semimembranosus tendon – 5 arms
• anterior • direct • capsular • inferior • obl popliteal ligament
• Anterior arm – may mimic displaced meniscal fragment
Meniscal Tear: mimic
Summary: menisci
• Know the normal anatomy
• Signal intensity and morphology
• Small meniscus? Find the displaced fragment
• Become familiar with common pitfalls
What the Surgeon Wants to Know
Peripheral Longitudinal Tear Good prognosis vs. M-C separation Radial tear Poor prognosis Avulsion post root med meniscus Articular cartilage Parameniscal cyst Look for horiz. tear Flap tear / Bucket handle tear Displaced tissue gutters / notch
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