Meniscal Tears

Mensical Tear Posterior Horn 1Mensical Tear Posterior Horn 2

 

Mechanism of Injuries

 

Rotational force incurred while joint partially flexed & extending

- caught between femoral & tibial condyles

- usually valgus & ER / varus & IR

 

Incidence

 

MM: LM 2:1

 

Medial Meniscus more common

- less mobile

- usually posterior horn tear

 

Acute ACL

- lateral Meniscus

 

Chronic ACL

- medial meniscus

 

Tibial plateau fracture

- 50% incidence

 

Relatively common in asymptomatic knees

- 13% < 45 years

- 36% > 45 years

 

Medial meniscus anatomy

 

C shaped fibrocartilage

- posterior horn larger than anterior horn

- capsular attachment on the tibial side is the coronary ligament

- thickening of the capsule from tibia to femur is deep MCL

 

Medial Meniscus NormalPosterior Horn Medial Meniscus Normal

 

Lateral meniscus

 

Semicircular

- covers a larger surface of the tibia than MM

- anterior and posterior horns attach closer to each other

- anterior horn adjacent to ACL

- posterior horn behind tibial eminence

- ligaments of Humphrey and Wrisberg are attached to posterior horn

- popliteal hiatus posteriorly

 

Lateral Mensicus NormalKnee Arthroscopy Popliteus

 

Microstructure

 

Circumferential type I collagen fibres

- radial fibres to anchor them

- more random mesh structure at surface

- fibrochondrocytes

 

Blood Supply

 

Development

- entirely vascular at birth

- inner 1/3 avascular by 1 year

- adult blood supply by 10

 

Outer 10 - 25% vascular

- genicular arteries

- perimeniscal capillary plexus

 

Inner 2/3

- nutrition via diffusion

 

Synovial fringe

- femoral and tibial surface

- does not contribute to the meniscal blood supply

 

Nerve supply

 

Similar distribution

- peripheral tears more painful than central tears

- proprioception

 

Function

 

1.  Transmit and distribute forces over plateau

- load sharing flexion > extension

- shock absorbing

 

Total medial meniscectomy

- 100% increase in contact stresses

 

Total lateral meniscectomy

- 200-300% increase in contact stresses

 

2.  Secondary stabilisers

- posterior horn resists anterior translation in flexion

- important in ACL deficient knee

 

Classification

 

1.  Longitudinal Tears

 

Mensical Tear Posterior HornMeniscal Tear Posterior Horn

 

Most common

- vertically oriented tear parallel to edge of meniscus

- usually of posterior part of meniscus

- may occur in either meniscus

- extent varies

 

A.  Incomplete 

- usually inferior surface

- may have been complete then healed

- very common posterior horn lateral meniscus after ACL rupture

 

Knee Arthroscopy Healed Meniscal Tear Undersurface Lateral MeniscusKnee Arthroscopy Healed Meniscal Tear Lateral Meniscus Top Surface

 

B. Complete

 

Mensical tear complete longitudinal

 

C.  Bucket handle 

- displaces into intercondylar notch

- may be central or peripheral

- cause of locked knee

- can damage chondral surface over time

 

Bucket Handle Tear MM displaced anteriorly arthroscopyMeniscus Bucket Handle Flipped Anteriorly

 

Mensicus Locked Lateral Bucket Handle

 

2.  Horizontal Cleavage

 

More common in older patient

- horizontal cleavage plane between superior & inferior surfaces of meniscus

- posterior 1/2 of MM

- mid-segment of LM

 

Meniscus Horizontal Tear

 

3.  Oblique

 

Vertically oriented full-thickness tear 

- runs obliquely from inner edge of meniscus out to body of meniscus

- if base posterior, referred to as posterior oblique tear & vice versa

 

4.  Radial 

 

Vertically oriented full thickness tear 

- extends from inner edge radially to periphery

 

Meniscal Radial Tear

 

Incomplete 

- doesn't extend to periphery

 

Complete 

- extends to periphery

 

Parrot beak tear 

- incomplete radial tear with anterior or posterior extension 

 

5.  Complex

 

Elements of all above

- usually in longstanding meniscal lesions

 

6.  Degenerative

 

Complex tear of degenerative meniscus / usually OA

 

Degenerative Meniscal Tear

 

Blood Supply Classification

 

Red - Red Tears

- peripheral 3 mm

- capsulomeniscal junction

- good blood supply

- both sides vascularised

 

Red - White Tears

- only one side of tear vascularised

 

White - White Tears

- peripheral

- neither side vascularised

 

Symptoms

 

History of injury

- twist with weight bearing

- may not be a specific injury especially in middle-aged patient

 

Swelling usually delayed 6 hours & mild 

- can be chronic from synovial irritation

- may be rapid haemarthrosis with capsular tear

 

Locking

- only with longitudinal tears / bucket handle tear

 

Giving Way

- may occur with other knee disorders

- i.e. loose body, instability, weak quadriceps

 

Signs

 

Effusion

 

Tenderness

- along periphery of meniscus

- along joint line

- pain secondary to synovitis in adjacent capsule

 

McMurray's Test 

- tests menisci posterior to collateral ligaments

- point heel towards meniscus testing

- positive test is palpable or audible snap or click

 

1. Fully flex knee

2. Place leg into full IR -> tests LM

3. Extend to 90°

4. Place leg into full ER -> tests MM

5. Extend to 90°

 

X-ray

 

Standard Knee Series

Exclude SONK / loose bodies / OCD / tumour

 

MRI Classification

 

Stoller 1987 J. Radiol.

 

Grade 0 

- normal homogeneous low signal intensity

 

Grade I 

- globular increase signal in meniscus

- doesn't reach either surface

 

Meniscus MRI Increased Signal

 

Grade II 

- linear increase signal, doesn't reach surface

- myxoid intra-meniscal degeneration / partially healed tear

 

Mensical Tear Incomplete

 

Grade III

- increased signal intensity communicates with meniscal surface

- 70-90% accurate for true tear

- accuracy MM > LM

 

Anterior Horn Meniscal Tear Stoller Grade 3Medial Meniscus Posterior Horn TearMRI Meniscus Tear Posterior Horn

 

MRI Pitfalls / Normal Findings or Variants

 

Ligaments of Wrisberg PMFL & Humphrey AMFL

 

Ligament Wrisberg

 

Transverse Anterior Meniscal Ligament

 

MRI Intermeniscal Ligament

 

Signs of bucket handle tear meniscus

 

1.  Double PCL sign

- medial Meniscus

 

Medial Meniscus Tear Double PCL

 

2.  Absent bow tie sign

- should see bow tie image on 2 consecutive sagittal slices of 5 mm

 

3.  Fragment in notch sign

 

Medial Meniscus Bucket Handle Tear Fragment in Notch

 

4.  Anterior flipped meniscal sign

- torn fragment flips over the anterior horn of the affected meniscus

 

Medial Meniscus Bucket Handle Tear Anterior Flipped MeniscusAnterior Flipped Meniscus Bucket Handle

 

5.  Truncated meniscus

 

Bucket Handle Tear Truncated Meniscus

 

Arthroscopy

 

Mainstay of diagnosis and treatment

 

Bone Scan

 

Don't forget SONK in differential

- 60 yr old female with normal x-rays

- acute onset pain

- AVN MFC

 

Should usually show up on MRI

 

Management

 

Surgical Indications

 

Painful locking / clicking with disability

Acutely locked knee

Repairable meniscus in combination with ACL injury

Repairable meniscal injury in young

 

Options

 

1.  Leave / non operative treatment

2.  Excise

3.  Repair

4.  Meniscal transplant

 

Non Operative Treatment

 

Essentially the asymptomatic patient

 

A.  Stable partial thickness (< 50%)

B.  Stable longitudinal < 1 cm long

C.  Small < 3 mm radial tears

 

ROM exercises + quads drill