Meniscus Flashcards
1
Q
What are the meniscus?
A
- 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
2
Q
What shape is the medial meniscus?
A
- 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
3
Q
What shape is the lateral meniscus?
A
- 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
4
Q
What are the names of additional ligaments that run from the posterior horn of the lateral meniscus to medial femoral condyle?
A
- Ligament of Henry- infront of PCL
- Ligament of wrisberg- behind PCL
5
Q
When does the meniscus appears?
A
- At day **45 **
- they differentiate directly from blastemal cells
6
Q
What is the meniscus like at birth and what happens with age?
A
- completely vascularised
- regresses by age 10
- by adulthood only the peripheral 10-30% remains vascular
7
Q
What is the histology of the meniscus?
A
- 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
8
Q
What are the types of fibrochondrocytes?
A
- 2 types
- Fusiform cells- found in superficial zone
- Ovoid cells- elsewhere in mensicus
9
Q
What is the 3 layers of collagen in mensicus?
A
- 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
10
Q
What is function of the meniscus?
A
- 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
11
Q
What precentage of compressive forces goes thru mensicus in flexion and extension?
A
- Flexion 85% in 90 degrees
- extension 50%
12
Q
What happens to the forces with partial meniscectomy?
A
- Increases contact stresses
- resection as a little as 15-34 % increases contact pressures by 350%
13
Q
What happens to meniscus in flexion?
A
- 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
14
Q
What plays a role in AP joint stability?
A
- 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
15
Q
Does the mensicus have a role in proprioception?
A
- It may due to the presence of type 1 & 2 nerve endings concentrated in the anterior and posterior horns
16
Q
Which meniscus is more commonly discoid?
A
- **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
17
Q
What is the classification of menisceal tears?
A
- Location related to blood supply
- tear pattern
18
Q
What is the blood supply to the meniscus?
A
- 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)
19
Q
What are the zones with the mensicus?
A
- Red: red zone - excellent blood supply
- Red: white zone- variable blood supply
- White:white zone- central /free edge= poor blood supply
20
Q
How does the zones help repair of tears?
A
- Peripheral tears are suitable for repair whilst central tears are unstable due to lack of healing potential
21
Q
What happens when a peripheral tear occurs?
A
- 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
22
Q
Decribe the types of menisceal tears?
A
-
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
23
Q
What is the criteria for menisceal repair?
A
- 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
