Bone and Cartilage

Types of cartilage

• Hyaline

• Fibrocartilage

• Elastic cartilage

Hyaline cartilage

Consists of chondrocytes

Appears glass and shiny looking

Hyaline Cartilage consists of what

chondrocytes and extracellular matrix (ECM)

Chondrocytes

Cells that make up the ECM. They settle into pits called lacunae. The chondrocytes group into pairs called isogenous groups with one another.

The job of the ECM

a specialized area that serves to absorb shock and acts as a smooth gliding area. Since the area is very empty, it acts as a great shock absorber

The ECM consists of

-80% water- which gives the hyaline cartilage to absorb compression

ex. a sponge being squeezed then bouncing back to place.

-15% collagen- provides a structural framework to the hyaline cartilage to ensure structural integrity

-Proteoglycans (sugar/protein molecules) - attracts water

The ECM of hyaline cartilage is non-mineralized and largely empty (unlike bone)

Overtime what happens to the cartilage?

They cartilage breaks down and chips away

Hyaline Cartilage ECM

is avascular (lacking blood supply, thus cannot self repair and heal) and aneural (not able to feel pain when damaged). It becomes painful when it impacts the bone

Where is hyaline cartilage found?

It is found at the ends of articulating bones in synovial joints, where it is called the articular hyaline cartilage

Articular hyaline cartilage

Hyaline cartilage that is found on the articulating surfaces on bones in the synovial joints

What does articular hyaline cartilage provide?

• provides a relatively friction free glide during joint movement

• It can be damaged due to obesity, over-use, and direct trauma

Down side of articular hyaline cartilage

Its ECM is avascular so it has no blood supply, thus it cannot self-repair

What happens when the AHC is damaged

It exposes the subchondral bone which is very painful. When subchondral bone rubs, it leads to osteoarthritis (OA)

Osteoarthritis is caused by what

results in bone rubbing against each other. Bone spurs are a common feature of this form of arthritis. When the spurs form, it leads to less mobility and more pain. It is important to keep the person moving. It severe cases, a joint replacement is needed.

Osteoarthritis

Typically age related, a progressive pathology

• When there is destruction of the AHC it allow subchondral bone contact between the articulating bone in the synovial joint (bone to bone contact)

It is:

-Progressive

-Painful and leads to decreased mobility

-Treatment may require a joint replacement

-Seen equally in males and females but usually seen in elderly

Rheumatoid arthritis (RA)

• Chronic immune disorder

It is inflammation of the synovial membrane

• It damages the subchondral bone, but spares the the articular hyaline cartilage

Instead of rheumatoid arthritis damaging the the AHC like in osteoarthritis, what does it damage

It damaged the subchondral bone and other organs, such as the the skin, lungs, and heart

What is the course like for Rheumatoid arthritis?

presents flare ups with periods of remission. It affects more females then males and has no age association.

Why does Rheumatoid arthritis affect more females

Estrogen regulates immune function and inflammation. While it is generally protective, sharp drops or spikes in estrogen can over-activate immune pathways

• Hence why there is a peak in menopause

Fibrochartilage

-Not very common

-Good at resisting twisting forces and compression, but it can only take so much

-avascular and aneural

Fibrocartilage components

Chondrocytes- the same cells found in hyaline cartilage, but they are arranged in rows instead of isogenous groups

ECM- same structure as in hyaline cartilage but the collagen fibers are slightly larger and they alternate in bundles with the chondrocytes

What does hyaline have that fibrocartilage doesn’t

Perichondrium

What typically occurs with too much twisting forces?

Knee meniscus tears are common due to too much twisting, typically seen in athletes. Because fibrocartilage lacks blood supply, these tears can be pain free.

Bone Components

The ECM is highly vascularized and has a rich sensory nerve supply. As a result you can feel pain when injured and the bone can self heal.

Compare the ECM in bone and cartilage

ECM in bone is mineralized and calcium makes up the majority of it

ECM in cartilage is not mineralized

Characteristics of bone

-Bone has a hard, rigid, mineralized extracellular matrix

-Has a generous blood supply and is full of sensory neurons

Parts of a bone

Compact/cortical and Spongy/cancellous bone

Compact/cortical

the outer surface of a bone

-makes about 80% of the skeleton

-dense and hard, provides strength to the bone

-makes the outer shell of bones

-provides a surface for tendon attachments

-the cortex is covered by a connective tissue sleeve called periosteum

-Contains trabeculae

Spongy/cancellous bone

-this is trabeculated (beam-like) bone deep to the cortex

-primarily found near the ends (or metaphysis) of long bones

-It provides the ability to resist and adapt to various biomechanical forces (where loading strength comes from)

-At the proximal and distal

When you palpate what are you touching

The periosteum around the compact bone

Osteopenia

Low bone density (the precursor of osteoporosis)

-Can be slowed

Osteoporosis

Significantly low bone density and fragility

-pathology is associated with age (elder, starts for women during menopause)

-stages

-end result is osteoporotic fractures commonly seen in the distal part of the radius, thoracic vertebrae, and femoral neck