Meniscus

Question 1

What are the meniscus?

Answer 1

• 2 crescent fibrocartilaginous structures interposed between the condyles of femur and tibia of the knee
• peripheral border is thick, convex adn attached to the capsule of the joint
• Inner border tapers to a thin free edge

Question 2

What shape is the medial meniscus?

Answer 2

• Semicircular
• 3.5cm length
• triangular x sectional area
• Asymmetrical- wider posterior horn than anterior horn
• attached firmly to posterior intercondylar fossa of the tibia directly anterior to the posterior cruciate ligament
• Anterior attachment more viariable- usually 7mm anterior to the anterior cruciate ligament insertion in line with the medial tibial tubercle
• peripherally attached to capsule of the joint being associated most firmly at the condensation in the capsule - deep medial collateral ligament

Question 3

What shape is the lateral meniscus?

Answer 3

• Almost circular
• covers larger area then Medial meniscus
• anterior horn attached to intercondylar fossa adjacent to ACL
• posterior horn attached to intercondylar fossa adjacent and anterior to the posterior horn of the MM
• peripheral attachment interupted by popliteus tendon
• no direct attachment to lateral collateral ligament
• loose attachment to periphery

Question 4

What are the names of additional ligaments that run from the posterior horn of the lateral meniscus to medial femoral condyle?

Answer 4

• Ligament of Henry- infront of PCL
• Ligament of wrisberg- behind PCL

Question 5

When does the meniscus appears?

Answer 5

• At day **45 **
• they differentiate directly from blastemal cells

Question 6

What is the meniscus like at birth and what happens with age?

Answer 6

• completely vascularised
• regresses by age 10
• by adulthood only the peripheral 10-30% remains vascular

Question 7

What is the histology of the meniscus?

Answer 7

• Fibrocartilagenous structure
• whose extracellular matrix is composed mainly of water 70% interlaced with collagen fibres surrounded by elastin,proteoglycans and glycoproteins
• cellular components= fibrochondrocytes
  
  • ​anaerobic cells with few mitochondria, which synthesize and maintain ECM

Question 8

What are the types of fibrochondrocytes?

Answer 8

• 2 types
• Fusiform cells- found in superficial zone
• Ovoid cells- elsewhere in mensicus

Question 9

What is the 3 layers of collagen in mensicus?

Answer 9

• Superifical
• surface
• middle
• majority of collagen fibres have a circumferential orientation following the C shaped curve of the meniscus
• there are a few radially arranged fibres- mainly in the superificial layer
  
  • may act as ties, providing stuctural rigidity against compressive forces and preventing longitudinal splitting

Question 10

What is function of the meniscus?

Answer 10

• Load transmission across the knee ** most important
• enhancement of articular deformity
• prevention of soft tissue impingment during joint motion
• role in anteroposterior (AP) stabilisation of the knee

Question 11

What precentage of compressive forces goes thru mensicus in flexion and extension?

Answer 11

• Flexion 85% in 90 degrees
• extension 50%

Question 12

What happens to the forces with partial meniscectomy?

Answer 12

• Increases contact stresses
• resection as a little as 15-34 % increases contact pressures by 350%

Question 13

What happens to meniscus in flexion?

Answer 13

• both meniscus LM >MM displace in an AP direction along the tibial plateau in the midcondylar parasagittal plane
• mensicus deform to remain constant congruity to tibial and femoral articular surfaces
• both aids load transmission and shock absorption
• conformity -> viscous hydrodynamic action required for full fluid film lubrication, assists in overall lubrication and circulation of the synovial fluid around the joint

Question 14

What plays a role in AP joint stability?

Answer 14

• Medial meniscus
• Signif > joint laxity in ACL deficient knees with medial meniscectomy cf ACL def knees with MM present
• Medial meniscectomy alone has no effect on AP laxity

Question 15

Does the mensicus have a role in proprioception?

Answer 15

• It may due to the presence of type 1 & 2 nerve endings concentrated in the anterior and posterior horns

Question 16

Which meniscus is more commonly discoid?

Answer 16

• **Lateral **( medial v rare 0.06-0.03%)
• incidence 4-15.5.%
• usually present in childhood- snapping/pain
• MRI diagnostic
• arthroscopic partial meniscetomy gives good short term results

Question 17

What is the classification of menisceal tears?

Answer 17

• Location related to blood supply
• tear pattern

Question 18

What is the blood supply to the meniscus?

Answer 18

• Peripheral blood supply from the lateral and medial geniculate arteries
• branches give rise to the perimenisceal capillary plexus
• orientated in circumferential pattern radial towards the centre of the joint
• penetration is 10-30% of mensiceal width ( red zone)

Question 19

What are the zones with the mensicus?

Answer 19

1. Red: red zone - excellent blood supply
2. Red: white zone- variable blood supply
3. White:white zone- central /free edge= poor blood supply

Question 20

How does the zones help repair of tears?

Answer 20

• Peripheral tears are suitable for repair whilst central tears are unstable due to lack of healing potential

Question 21

What happens when a peripheral tear occurs?

Answer 21

• A fibrin clot rich in inflammatory cells forms through which a vessel and undifferentiated mesechymal cell proliferation occurs with the creation of a fibrovascular cellular scar tissue

Question 22

Decribe the types of menisceal tears?

Answer 22

• Vertical
  
  • longitudinal: commonly peripheral bucket handle tear
  • radial : occur in vertical plane, commony at lateral aspect of LM, asymptomatic when small
• Horizontal
  
  • pure cleavage
  • partial cleavage ( flap tears)
• Complex
  
  • combination of above patterns assoc with degenerative menisceal tissue

Question 23

What is the criteria for menisceal repair?

Answer 23

• Location
  
  • red:red zone 0-3mm from periphery
  • red:white 3-5mm from periphery
• tear pattern
  
  • vertical longitudinal tears longer than 1cm and radial tears extending into red zone
• tissue quality
  
  • not indicated in macerated and degenerative tissue