Menisci Aging, pathology and rehab Flashcards
Functions:
Load distribution decreases stress Shock absorption Joint stability - against translation Proprioception Lubrication - compress fibrocartilagenous structure releases SF > protects articular cartilage
semi-lunar shaped
increases congruency
increase contact
decrease stress
Medial meniscus is:
- longer A-P
* larger posterior hor
Lateral menisci is more:
- variable
- mobile
Meniscal coverage of plateau:
Medial 50-75% - but greater load med. More bound/moves less out of road therefore injured more
Lateral 75-93%
Internal structure: composition
Early development = all cells similar Adult = outer zone – ‘fibroblast-like’
Long cell extensions = communication!
Collagen Type I = 80% dry weight
= inner zone – ‘fibrochondrocytes’
Collagen = 70% dry weight Type II > Type I
=superficial zone - progenitor cells
Proteoglycans > in the inner 2/3 ~1/8 of that in hyaline
- fibrocartilage, antisotropic
Internal structure:
collagen alignment
Anisotropic:
collagen fibers orient with the local axis of stress
* lines parallel to resist tensile stress
moves out (collagen T1) > * Radial fibres also present in midzone and especially on surfaces (tibial > femoral)
Vascularisation
Birth = 100%
~10 years = 10-30%
Adult = peripheral 10-25%
Innervation:
Coronal section of medial compartment
PCP = perimeniscal capillary plexus
Outer 1/3 ‘vascular zone’ Mechanoreceptors esp horns
* if have inner tear, more difficult to heal
Biomechanics:
Compressive loading generates significant radial & circumferential stresses:
- tensile stress from horns and forces out radially
turns radial > circum. stress
Meniscal translation 250 during movement
both menisci translate post. on tibia and post. horn moves towards centre of joint
In full flex = compression of post. horn of meniscus
“The medial and lateral menisci translate posteriorly an additional -1.7mm and 0.9mm respectively and
medially by 1.7mm and -5.6mm respectively during joint loading.”
Ultimate tensile strength
- relative to fibre alignment
- Parallel 6.3-8MPa
- Perpendicular <1MPa
- Increases with age (cross-linkages)
Aging:
earliest changes occurred predominantly along the inner rim anterior horns of both medial and lateral menisci were less affected by age and OA
• Surface roughness with severe fibrillation
• Cellular senescence > decreased cell density,
• the appearance of acellular zones,
• mucoid degeneration
• Increase in collagen amount, fibril diameter & cross-link
aging 2
starts along inner rim
- once surface protective layer broken, surface more permeable and lose fluid therefore ECM substance effected
Pathology: OA related changes
Menisci from OA joints showed:
•severe fibrocartilaginous separation of the matrix
• extensive fraying
• tears (major pathology, if tears > fails)
• calcification
• abnormal cell arrangements included
• decreasedcellularity,
• diffusehypercellularity, • cellular hypertrophy,
• abnormal cell clusters.
Pathology:
Tears:
- Traumatic - acute incident
- Degenerative - fatigue/accumulation
