5-Meniscus and IV Discs Flashcards
What are the 2 primary functions of the meniscus?
I)Distribute load of the body weight
II)protect articular cartilage at knee joint
What are the 3 minor functions of the meniscus?
I) provide passive stability
II) lubrication
III) proprioception
What is a viscoelastic structure?
A structure whose mechanical properties depend on the rate of loading
How does the viscoelastic structure of the meniscus relate to the support capabilities?
allows it to dampen weight bearing load
What happens to the structure of the meniscus when it’s compressed?
Deformation of the fibrous structure –> flow of gel through the fibers –> resistance of the flow allows energy/shock absorption through the loading on the meniscus
How much less is a joint able to absorb shock if the meniscus is removed?
20% less capable
How much is there a decrease in contact area between femoral condyle and tibial plateau if the meniscus is removed?
60%
What is the load distribution in the medial meniscus in a fully extended knee?
50% of the compartmental load
What is the load distribution in the lateral meniscus in a fully extended knee?
75% of the compartmental load
What is the load distribution in the both menisci in a flexed knee at 90 degrees?
85%
What is passive joint stability?
describes what provides stability when the main ligaments are injured
What provides passive joint stability to prevent anterior tibial subluxation in the event the ACL is injured?
Medial meniscus
What is the function of the ruffini end organs at the meniscus?
sensitive to skin stretch
What is the function of the golgi tendon organs at the meniscus?
monitors changes in muscle changes
What is the function of the Pacinian corpuscles at the meniscus?
sentitivity to pressure and vibrations
Where in the meniscus is the largest amount of nerve endings?
anterior and posterior horns of menisci
What are the substances a meniscus is contained of?
A) Water B) Cells C) Collagen D) proteoglycans E)Glycoproteins
What are the the cell types at the periphery of the meniscus?
spindle shaped and fibroblast like
What are the functions of the fibrochondrocytes (ovoid) cells of the inner avascular portion of the meniscus?
Synthesize the extracellular proteins
Which molecule makes up to 75% of the dry weight of the meniscus?
Collagen
What are 4 other moelcules, besides collagen, that makes up the dry weight of the meniscus?
I) aggrecan
II) chondroitin 4-sulfate
III) fibronectin
IV) other glycoprotein’s
What molecule makes up 70% of the wet weight of the meniscus?
water
What types of collagen are present at the meniscus?
A) 90% of collagen in the meniscus is fibrillar type I
B)Type II, III, V, VI make upt the remainder
What type of shape is most of the collagen Type I arranged in the matrix?
circles
How is the arrangement of collagen type I made for load stresses?
I)withstand circumferential tension (“hoop stress”) developed during normal loading.
II) without this meniscus would be extruded from the joint space
What is the anatomy of the medial meniscus?
I)Semicircular, 3.5cm in diameter.
II)Cover 60% of the medial tibial plateau articular cartilage.
III)Less mobile than lateral meniscus anterior stabilizer, but more vulnerable to tearing.
What is the anatomy of the lateral meniscus?
I)Covers up to 80% of the lateral tibial plateau articular cartilage.
II(Anteriorly attached to the tibia behind the attachment of the ACL.
III)Along peripheral margin, loosely attached to the joint capsule by the coronary ligament.
IV)Absence of attachment of meniscus to LCL allows passage of the popliteal tendon b/w the lateral meniscus and the LCL – the popliteal hiatus.
V)Behind intercondylar eminence and anterior to posterior horn of the medial meniscus the posterior horn of the lateral meniscus is attached to the tibia
How much of the medial tibial plateau articular cartilage does the medial meniscus cover?
60%
How much of the lateral tibial plateau articular cartilage does the lateral mensicus cover?
80%
Where on the medial and lateral menisci does the transverse intermeniscal ligament connect?
anterior horns
What does the coronary ligament attaches meniscus to?
joint capsule + tibial plateau
Around the periphery of the meniscus, what ligament is the capsule connected to?
medial collateral lig.
What part of the meniscus is attached to the posterior intercondylar fossa b/w lateral meniscus and posterior cruciate ligament?
posterior horn
What is the main artery that supplies the meniscus?
popliteal artery, which divides into the medial and lateral geniculate arteries
What are the vessels that are orientated in a circumferential pattern with radial branches extending into the meniscus along its periphery?
perimeniscal vessels
What occurs during the initial formation of the vascular supply?
abundance of cells and vascularity.
What occurs during the neonatal development of the vascular supply?
number of cells and extend of vascularity decrease.
What occurs during the development of the vascular supply at birth?
vascular network extends from peripheral perimeniscal capillary plexus to the free central margin of the meniscus.
What occurs during the development of the vascular supply suring the first few months of life?
vascularity decreases such that by the 9th month the inner third of the meniscus is avascular. This process continues – in adulthood only the peripheral 10-30% is vascular.
What occurs during the cell count as you age?
I)Similar to vascular supply.
II)Replete with cells at birth, meniscus becomes progressively less cellular with age.
III)These changes are believed to be induced by the increased joint motion and weight bearing in early child development.
What changes to the proteoglycans as you age?
changes with age with an increase in chondroitin 6-sulfate and a decrease in chondroitin 4-sulfate
What are the 5 functions of the intervertebral disc?
I)Stabilizes the spine.
II)Helps maintain alignment.
III)Allows motion between vertebral levels.
IV)Absorbs energy.
V)Distributes loads applied to the spine.
What types of cells make up the anulus fibrosis?
fibrocartilage, with the outer ring as type I collagne and the deep ring as type II
What types of cells make up the nucelus puloposus?
proteoglycans (which interact with water)
What occurs during a herniated disk to the anulus fibrosis and the nucleus puposus?
Protrusion of the nucleus pulposus through tears in the annulus fibrosus
Why does the nucleus pulposus usually go through the posterior aspect of the disk rather than the anterior aspect?
Anterior annulus fibrosus is thicker than posterior
Are all the disks (from cervical–>lumbar) the same height and diameter throughout the spine?
No. Disks increase in height and diameter from the cervical to the lumbar spine.
What is the shape of the IV disks to give the lordotic curve to the cervical spine?
The anterior aspects of the IV disk are thicker than the posterior aspects.
True or False: the thoracic disks are uniform in height from anterior to posterior
true (thr normal kyphosis is due to the shape of the thoracic body itself)
What are the outer edges of the discs are attached to the vertebral bodies by small collagen fibers called?
Sharpey’s fibers
True or false: there is a direct blood supply to the central IV disk
False
If there is such a poor blood supply to the disk, how can it get nutrients?
Small vessels penetrate the outer ring of the ANULUS FIBROSUS. Nutrition of the inner disk is by DIFFUSION.
What happens to the water content of the IV disks as you age?
The high water content of the nucleus pulposus decreases with age
What happens to the aggrecan molecules as you age?
The proportion of proteoglycans that do not bind water progressively increases and the size of the aggrecan molecules decreases
What are the 2 most common clinical disorers of the axial skeleton?
A)Herniated nucleus pulposus
B)Degenerative disease of the spine
What happens to the nucleus pulposus as you age?
A)The most extensive changes occur in the nucleus pulposus
B)There is a sharp decline in the number of viable cells and concentrations of proteoglycans that bind water.
C)The aggregate proteoglycans become fragmented with an increase in the concentration of collagens and noncollagen proteins as dense granular material accumulates throughout the extracellular matrix.
D)Therefore, the nucleus pulposus becomes firm and white rather than soft and translucent.
