Joints, Articular cartilage and Synovial fluid L3: Menisci- Aging, pathology & rehabilitation Flashcards
What are the 6 functions of menisci?
- Load distribution decreases stress
- Semi-lunar
- Flat tibial plateau & round femoral condyles
- Doubled contact by fibula
- Shock absorption
- Joint stability
- Against translation
- Proprioception
- Margins innervated feeback
- Lubrication
- Compression released synovial fluid
- Protects articular cartilage
Gross structure of menisci
The medial meniscus is ______(longer/shorter) from AP than the lateral meniscus.
Longer
The medial meniscus has a ______(larger/smaller) posterior horn than the lateral meniscus.
Larger
The medial meniscus is ______(more/less) variable than lateral meniscus.
Less
The medial meniscus is ______(more/less) mobile than lateral meniscus.
Less When weight-bearing, it has the opportunity to move out of the way
Does the medial or the lateral meniscus cover more of the tibial plateau?
Lateral covers more
Why does the medial meniscus cover less of the tibial plateau?
The medial menicus proportionally covers less of facet because femur and tibia surfaces are also larger = greater weight bearing = less likely to move out of way = injury
Which menisci is more prone to injury?
Medial because… greater weight bearing = less likely to move out of way = injury
What is the composition of menisci?
- Early development = all cells similar
- Adult = outer zone – ‘fibroblast-like’ o Long cell extensions = communication! o Collagen Type I = 80% dry weight
- = inner zone – ‘fibrochondrocytes’ o Collagen = 70% dry weight Type II > Type I
- = superficial zone - progenitor cells o Decrease as age –? Less capacity to repair stem cells
What are the 3 characteristics of collagen alignment of menisci?
- Anisotropic
- Principal direction = circumferential
- Type I fibres (strong outside)
- Radial fibres also present in midzone and especially on surface (tibial > femoral)
- Radiating out from inner to outer rims are focused on tibia
What is the vascularisation and innervation of menisci?
Was vascularization at birth –> recedes to only 10-20% of outside
What is the vascularisation of menisci like?
- • Birth = 100%
- ~ 10 yrs = 10-30%
- Adult = peripheral 10-25%
- Tear in inner rim = poor ability to heal
What is the innervation of menisci?
- Outer 1/3 vascular zone
- Mechanoreceptor esp. horn
- Proprioception
What are the biomechanics of menisci?
- Compressive loading generates significant radial & circumferential stresses
- flat surface –> load coming down through curved surface –> wedge shaped meniscus –> push meniscus outwards –> meniscal horns are attached to tibia –> weight bear –> tensile force –> radially directing out circumference –> radial fibres circumferential hoop stress
What happens in meniscal translation during movement?
Translate posteriorly and medially during joint loading (weight bearing)
What is the ultimate tensile strength of menisci?
- Relative to fibre alignment
- Parallel 6.3-8MPa
- Perpendicular <1MPa
- Increases with age (cross-linkages)
Modulus of elasticity. Which forces can menisci withstand? (most to least)
Tension > Compression > Shear
What is ageing?
Earliest changes occurred predominantly along the inner rim
Which horn is least affected by age and OA?
Anterior horns of both medial and lateral menisci
- Surface roughness with severe fibrillation
- Cellular senescence cell density
- the appearance of acellular zones,
- mucoid degeneration
- collagen amount, fibril diameter & cross-link
What are some characteristics of menisci from OA joints?
- severe fibrocartilaginous separation of the matrix
- extensive fraying
- tears
- calcification
- abnormal cell arrangements included
- decreased cellularity,
- diffuse hypercellularity
- cellular hypertrophy
- abnormal cell clusters
What are the 2 types of meniscal pathological tears? How are they different?
-
Traumatic
- Acute
-
Degenerative
- Accumulative, fatigue
What are 3 types of diagnosis for meniscal pathology?
- Subjective & objective examination
- Arthroscopy = gold standard
- MRI sensitivity 93% MM &79% LM
- specificity 88% MM & 96% LM
What are the 6 ISAKOS classifications of meniscal tears?
- Depth 2. Location 3. Tear pattern 4. Longitudinal 5. Horizontal 6. Radial
ISAKOS classifications of meniscal tears: What are the 2 types of depth classification?
- Partial
-
Complete
- complete from surface to surface or layers
- superior to inferior
- vertical (inner to outer)
- complete from surface to surface or layers
ISAKOS classifications of meniscal tears: What are the 2 types of location classification?
- Rim
- circumferential zone 1,2,3
- Radial
- Anterior
- Middle
- Posterior
ISAKOS classifications of meniscal tears: Longitudinal
Vertical = superior to inferior (perpendicular to tibial plateau) - split between zone 1 and 2
- Young athletic
- +/- ACL
- Zone 1 & 2
- Posterior
- Bucket-handle
- meniscus is in the way- move jt around to get free
ISAKOS classifications of meniscal tears: Horizontal
Parallel with tibial surface
- Degeneration (usually older)
- Split into inferior/superior
ISAKOS classifications of meniscal tears: Radial
- Most common type in young adults
- At junction of 1/3s
- Starts at inner rim (avascular and hyaline cartilage)
What are the 3 rehabilitation options for meniscal pathology?
- Repair
- Menisectomy
- more meniscus removed –> less contact area –> less shock absorption –> more stress on joint
- Partial
- try to only trim or repair
- Complete
- Increase 235%-335% increase in peak local contact load
- Tissue engineering
- Autologous/allogeneic/exogeneic
- Stem cell
What are the 5 injuries that lead to damage of hyaline cartilage?
- Acute trauma
- Post-traumatic
- Prolonged overloading
- Prolonged immobilisation
- Local or systemic inflammation
How does acute trauma lead to damage of hyaline cartilage?
primary injury due to impact force that can cause chondrocyte death, damage to collagen and loss of proteoglycans
How does post traumatic injury lead to damage of hyaline cartilage?
secondary to ligamentous instability or meniscal damage or muscle imbalance –> altered joint kinematics
- possible increased translation / recurrent instability / change in bearing area –> loading of unconditioned cartilage
- post-heamarthrosis (as with ACL rupture) –> biochemical change to synovial fluid with possible negative effect on chondrocyte activity
How does prolonged overloading lead to damage of hyaline cartilage?
e.g. chronic obesity –> fatigue failure, prolonged postures
How does prolonged immobilisation lead to damage of hyaline cartilage?
- decreased nutrition as a result of decreased synovial flow in/out of cartilage
- decreased mechanical stimulus to the chondrocytes to maintain ECM
How does local or systemic inflammation lead to damage of hyaline cartilage?
inflammatory markers (chemicals) affects chondrocytes –> produce proteolytic enzymes –> degradation of ECM
What are the 4 factors affecting the ability of hyaline cartilage to repair?
- Avascularity – inability to heal via inflammatory response; decreased O2
- Low cellular density – greater relative portion of ECM to be maintained by each cell
- Low metabolic activity – low turnover of ECM
- Inability of chondrocytes to migrate to site of injury
