Biomechanics Exam V: Mechanics of Articular Cartilage

Where is the most amount of cartilage found in the body?

the hips, knees, and shoulders

_____ joints have articular cartilage at the end of bones.

Diarthrodial

Diarthrodial Joint

a freely moveable synovial joint

What is articular cartilage?

a type of connective tissue that is thin, but densely packed and relatively transparent in appearance

Articular cartilage lacks what three things?

blood vessels, nerves, and lymphatic connection

What are the two primary functions of articular cartilage?

• to cushion / absorb impacts at joints

• reduce friction

Articular cartilage is the ____ abundant cartilage in the body.

MOST

Chondrocytes

cartilage cells

What does articular cartilage contain?

• chondrocytes

• matrix

• collagen

Collagen provides ___ & __ in articular cartilage.

strength and structure

What are the three layers of articular cartilage from the surface downward?

1. Superficial Zone

2. Intermediate Zone

3. Deep Zone

Superficial Zone

The outermost layer of articular cartilage, where chondrocytes are flattened and compact

The Superficial Zone accounts for ___ percent of the thickness in articular cartilage.

10-20%

Intermediate Zone

the middle layer of articular cartilage composed of round chondrocytes that are randomly arranged and lots of matrix

The Intermediate Zone accounts for ___ percent of the thickness in articular cartilage.

40-60%

Deep Zone

the innermost layer of articular cartilage characterized by chondrocytes arranged in columns and a dense extracellular matrix

The Deep Zone accounts for ___ percent of the thickness in articular cartilage.

30%

How do the collagen fibers change from superficial to deep in articular cartilage?

they become more like bone and are organized in a more perpendicular arrangement to the surface, providing additional support and resistance to compressive forces

Articular cartilage has a high ____ content.

water

What are the important roles articular cartilage plays?

1. shock absorption

2. creates lubrication between joints

3. brings nutrients in and pushes waste out

How would you describe articular cartilage?

strong, yet flexible

Rank the layers of articular cartilage by water content.

1. Intermediate zone

2. Deep zone

3. Superficial zone

What zone has the most deformation and why?

the intermediate zone has the most deformation due to its high water content and space to move

Describe the orientation of collagen in articular cartilage.

• collagen is arranged parallel to the surface in the superficial zone

• collagen has a more random orientation in the intermediate zone

• collagen is arranged perpendicular to the surface in the deep zone

• collagen fibers tend to intersect with one another when they rise to the surface

How are collagen fibers and proteoglycans oriented on a microscopic level and what is their collective function?

collagen fibers are crossed with proteoglycans and hyaluronic acid, giving articular cartilage its structural integrity.

As water is drawn into articular cartilage…

• nutrients comes in

• articular cartilage swells and its pressure increases

As water is drawn out of articular cartilage…

• waste is pushed out

• cartilage becomes compressed

• volume and pressure decrease

What is essential to cartilage function?

appropriate loading of muscles and joints

What is the mechanical behavior of articular cartilage?

• multiphasic response to loading: the solid matrix, water, and ions all respond to a load

• compression

• interstitial fluid phase: the fluid leaves the cartilage, leading to decreased volume and increased solid phase stress

• porous-permeable solid phase: the solid matrix allows fluid movement under load.

How do the different layers of articular cartilage respond to a load?

1. the superficial layer tries to take the bite out of the initial force

2. the intermediate layer absorbs shock by shifting its water weight

3. the deep layer acts as an anchor and holds the other two layers in place so they can perform their function

When do problems arise with articular cartilage?

when compression is combined with sliding / sheering forces, which can cause cartilage to tear