Lecture 11: Fibrocartilage

Where is fibrocartilage found?

Found inside of joint (can divide the joint into two functional units)

What type of collagen is most prominent in fibrocartilage?

Type I collagen (chondrocytes synthesize and secrete this)

What are the roles of fibrocartilage?

• Increase joint congruency

• Assist with joint lubrication

• Protect edges of joint

• Act as a shock absorber

• Act as load bearers (transmit loads)

In normal, healthy tissue, menisci should be ________, ________, and ________

In normal, healthy tissue, menisci should be smooth, glistening, and intact

According to Dr. Evans’ slides, the meniscus is a ________ tissue

According to Dr. Evans’ slides, the meniscus is a substantial tissue

What type of shape is the meniscus? Where does it attach?

Semi-lunar structure that attaches to the tibial plateaus

When is the meniscus susceptible to injury?

During loaded, rotational activities (sports)

What is the function of the meniscus?

• Acts as a buffer to the articular structures

• Dampens impact (like a shock absorber)

• Increases stability of the joint

• Distributes load

• Protects the articular cartilage and bony surfaces

The meniscus is responsible for __% of the load in the knee

The meniscus is responsible for 70% of the load in the knee

Meniscus removal leads to increasing _________ load by about __ times.

Meniscus removal leads to increases compressive loads by about 5x

Without the menisci, what happens to the load? Where does the area of loading become?

Load becomes more localized with smaller surface area

Area of loading becomes the center of the tibial plateau

What components of the load are affected by menisci?

Magnitude and distribution of the load are affected by menisci

The ability of menisci to form a _______ matrix is dependent upon ________.

The ability of menisci to form a solid matrix is dependent upon permeability

If permeability of the meniscus increases, what happens to its efficacy?

Meniscus is less effective

T/F: There is a linear relationship of menisci thickness to articular cartilage

False! They have an inverse relationship; where one is thick the other is thinner

(e.g., outer edge meniscus is MUCH thicker so the articular cartilage is very thin)

What % of meniscus structure is water?

70% water

Proteoglycans account for __% of the dry weight of the meniscus

Proteoglycans account for <10% of the dry weight of the meniscus

For the meniscus, collagen is about ____% of organic solids (type I)

For the meniscus, collagen is about 60-90% of organic solids (type I)

T/F: Menisci are aneural and void of lymphatics

True

Where is the vascular supply located for the meniscus?

Along the periphery (outer 1/3)

T/F: Pain does not come from the meniscus

True

T/F: Menisci tissue is anisotropic

True!

T/F: There is significantly more proteoglycans in the menisci than articular cartilage

False! There is significantly less proteoglycans in the menisci (indicating that it is a fiber rich structure)

What are the cells of the meniscus called?

Fibroblasts (very few of them)

What is the “red zone” of the meniscus?

Vascular portion / outer region of the meniscus

The “red zone” of the meniscus is made up of about __% dry weight type __ collagen

The “red zone” of the meniscus is made up of about 80% dry weight type I collagen

What are the cells like in the “red zone” of the menisci?

Cells are spindle-shaped and are more “fibroblastic-like” (it behaves kind of like lig/tendon)

What is the “white zone” of the meniscus?

Avascular / inner region of the meniscus

The “white zone” of the meniscus is made up of __% collagen. What percentage of that is type I and type II?

The “white zone” of the meniscus is made up of 70% collagen.

60% of that is type II (majority)

40% is type I

T/F: The “white zone” of the menisci contains a greater portion of proteoglycans

True! (mostly aggrecan, but also biglycan and decorin)

What are the cells like in the “white zone" of menisci?

Cells are more chondrocyte-like (they behave more like articular cartilage)

The superficial layer of the meniscus has what type of cells? What is their purpose/function?

Small and round cells — they disperse tensile load

What are the three layers of collagen fibers?

• Superficial Layer

• Intermediate Layer

• Inner-Most / Deep Layer

What is the type and arrangement of the collagen fibers in the superficial layer?

• Fine collagen fibrils (predominately type I)

• Randome woven matrix

The intermediate layer is approximately ___ microns from the surface

The intermediate layer is approximately 100 microns from the surface

What is the arrangement of the intermediate layer?

• Collagen bundles are large, rope-like

• Arranged circumferentially around the semilunar meniscus

• Smaller, radial fibers reinforce the structure by tying the larger fiber bundles together

Radial fibers (located in the intermediate layer) have a higher ______ modulus/strength.

Radial fibers (located in the intermediate layer) have a higher tensile modulus/strength.

In the intermediate layer, what fibers detect the compression force?

Radial fibers

What is the arrangement like in the inner-most / deep layer?

• Randomly arranged fibers

• More proteoglycans

• (more “articular cartilage like”)

When considering the layering of collagen fibers, the outside looks like ________ and the inside looks like ________.

When considering the layers of collagen fibers, the outside looks like tendon/ligament and the inside looks like articular cartilage

If compression is applied, it will cause a ______ force across the surface — the ______ fibers are being pulled and create ______ and the __________ fibers place pressure on the 3rd layer.

If compression is applied, it will cause a tensile force across the surface — the radial fibers are being pulled and create tension and the circumferential fibers place pressure on the 3rd layer

Circumferential fibers and radial fibers are part of which layer?

Intermediate / 2nd layer

T/F: The medial and lateral menisci are essentially the same in their arrangement

False!

Describe the arrangement of the lateral meniscus.

• Has the same arrangement throughout (e.g., same arrangement in posterior horn and anterior horn, etc.)

• Type I collagen fiber bundles that are highly oriented parallel to the periphery of the tissue

Describe the arrangement of the medial meniscus.

Collagen bundles have significantly less circumferential organization in the posterior aspect

In which meniscus (medial/lateral) does more injury tend to occur?

Medial meniscus

Considering the arrangement and organization of the medial and lateral menisci, what does this mean regarding the forces they receive?

• Lateral aspect gets more compressive forces

• Medial aspect gets more gapping

• Think about standing and how we have knee valgus

How does the meniscus receive nutrients?

Fluid flow in and out of tissue during cyclic compression

• Weeping is occurring but not to the extent that is seen in articular cartilage

The meniscus is more/less permeable than articular cartilage?

The meniscus is less permeable than articular cartilage

Where is the magnitude of compressive loading the greatest on the menisci?

• Superior surface of both medial and lateral menisci

• Along the central “strip” of each structure

Load bearing capacity is greater in which meniscus (medial/lateral)?

Greater in the lateral meniscus (because it is more organized and behaves with hoop stress)

Normal knee motion is typically describing the meniscus as…

Bending with knee flexion

The meniscus has properties of an __________ solid

The meniscus has properties of an incompressible solid

What percent of the population has direct attachment with the posterior horn of the lateral meniscus via the oblique popliteal ligament?

50%

The meniscus, in general, has a lower _______ modulus and a higher _______ modulus

The meniscus, in general, has a lower compressive modulus and a higher tensile modulus

T/F: The stress-strain curve of the meniscus is not truly linear

True

What does it indicate if a stress-strain curve is not linear?

Indicates that all stresses can cause plastic deformation

Failure of the meniscus occurs at ____% elongation

Failure of the meniscus occurs at 25-40% elongation

How does the anterior portion and the posterior portion of the menisci differ in terms of their stress-strain relationship?

• Anterior portion fails at higher strain rates but lower stresses than other areas

• Posterior meniscus has a lower modulus but a higher max stress

What is hoop stress?

• As we know, collagen resists tensile strength

• In the meniscus, the collagen are arranged circumferentially

• As tensile loads are resisted, the collagen is loaded as hoop stress

In what direction are menisci stiffer?

Menisci are stiffer in the circumferential direction (as opposed to the radial direction)

The medial meniscus (posterior portion) has considerably lower ______ strength and modulus

The medial meniscus (posterior portion) has considerably lower tensile strength and modulus

Where does stress focus on the lateral meniscus? What does this mean?

Stresses focus on the intermediate portion and secondarily on the posterior portion

Means more stress concentration areas (and therefore more susceptible to injury)

Where does the lateral meniscus tend to split?

Intermediate region

Where does the medial meniscus tend to split?

Posterior region

The radial modulus is ___ times lower than the circumferential modulus

The radial modulus is 10 times lower than the circumferential modulus

T/F: When the meniscus tears, the remaining fibers are able to maintain the mechanical functionality required for the meniscus

True!

When the meniscus is injured, how is stress transferred?

Radial “tie” fibers transfers stresses to the remaining intact circumferential collagen fibers

A tear needs to reach about ___% of the meniscus width before tibial contact stresses increase

A tear needs to reach about 90% of the meniscus width before tibial contact stresses increase

Why are cortisone injections not good for a meniscal injury?

Because of the close proximity of the meniscus to articular cartilage

Are NSAIDs okay for a meniscal injury?

May be okay initially, but there are long-term concerns

How long does it take fibrous scar tissue to form? Does it act like fibrocartilage right away?

Take 10 weeks for fibrous scar tissue to form; but it takes months for it to act like fibrocartilage

How would you treat a meniscus with exercise?

• Treatment tends to be like articular cartilage

• We want some cyclic compression for nutritonal health

The potential for wear (on the meniscus) increases when the joint goes from ______ loading to ______ loading

The potential for wear (on the meniscus) increases when the joint goes from static loading to high loading

(ease into exercise with warm up of joints)

What rate of loading is the most protective?

Moderate rate of loading (more protective than fast or slow)

What is a meniscectomy? What does it lead to?

Removal of part or all of the meniscus

• Either will increase the incidence of premature OA secondary to shifting load onto the articular cartilage

What are the cells of the TMJ disc called?

Fibroblasts (few cells)

T/F: The TMJ disc is avascular and aneural

True!

What type of collagen is the TMJ disc mostly made up of?

Majority type I collagen (with some type II fibers — especially centrall)

The intermediate band of the TMJ has a relatively high concentration of _____ for a tissue that has so many _____ oriented collagen fibers

The intermediate band of the TMJ has a relatively high concentration of aggrecan for a tissue that has so many parallel oriented collagen fibers

T/F: The intermediate band looks like a ligament except is has a low percentage of GAGs

False! The intermediate band does look like a ligament but is has a high percentage of GAGs

What does the anterior and posterior band of the TMJ disc “look like”?

Looks like articular cartilage

What is occurring at the TMJ during passive movement?

The superior and inferior lamina of the disk will basically hold it in place and or “leave it in-line with where the mandible articulates with the temporal bone”

You can sort of think of it as ligaments holding it in place

What is occurring at the TMJ during active movement / forceful opening?

• Contraction of the lateral pterygoid m.

• Elastic properties of lamina primarily maintain control of disc (while the suprahyoids and inf. fibers of lateral ptergoid translate condyle and disc forward)

• NOTE - the superior fibers of the lateral pterygoid are able to control the disc (attachment) along with the collateral ligaments on the lateral portion of the disc, but there is controversy whether the superior lateral pterygoid is active during opening)

What is occurring at the TMJ during relaxed opening?

• Lateraly pterygoid m. is relaxed

• Passive elastic properties of the superior lamina applies as posterior tractive force to maintain the disc within the mandibular fossa correctly

What does the stress-strain curve of the TMJ disc look like?

Looks like the stress-strain curve for tendon or ligament (probably because most of testing has been on intermediate band)

Are viscoelastic properties (hysteresis, creep, and stress relaxation) present in the TMJ disc?

Yes! It is very similar to tendon/ligament

Reaches equilibrium ~5 min

T/F: With the TMJ disc, there is compression only with active motion or closure

True!

T/F: Deformation of the TMJ disc is the same for passive and active motion

False!

Deformation is different in passive vs active motion

Loss of the _______ band seems to lead to _________ of the TMJ

Loss of the posterior band seems to lead to instability of the TMJ

What is the fracture pattern of the TMJ disc?

Holes / tears of bilaminar retro discal tissue

T/F: There is a psychological component to TMJ pain

True!

T/F: Aging also leads to changes of the TMJ disc just like tendon/ligament and articular cartilage

True! (older you get → less healthy it is)

What should exercise / physical therapy be focused on for TMJ disc pain (or injury)?

• Focus on minimizing pain

• Improving muscular balance (soft tissue mobilization)

• Lateral pterygoid muscle strengthening

If we are treating TMJ disc pain with exercise / physical therapy, what should the reps be? Why?

Reps should be less compared to other joints because the TMJ is constantly being used

T/F: Surgery is the best choice of treatment for the TMJ

False!

Surgery is often recommended but outcome studies demonstrate surgery is often the poorest choice of treatment

Intervertebral discs are ___ the height of the spinal column

Intervertebral discs are 1/3 the height of the spinal column

T/F: Intervertebral discs are the largest avascular structure in the body

True!

T/F: Intervertebral discs respond to both high impact loads (running and jumping) and low impact lows (standing and sitting)

True!

What are the two parts of the intervertebral disc?

Composed of the nucleus pulposus and annulus fibrosis