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