Physiology of Joints

Question 1

What are the three types of joints?

Answer 1

1. Synovial
2. Fibrous
3. Cartilaginous

Question 2

Within a synovial joint, what is the inner aspect of the fibrous capsule lined by?

Answer 2

Synovial membrane

(composed of vascular connective tissue with capillaries and lymphatics)

Question 3

What type of cells are synovial cells and what is thier function?

Answer 3

Fibroblasts

They produce synovial fluid

Question 4

What is a simple synovial joint?

Answer 4

A synovial joint with one pair of articular surfaces

Question 5

What is a compond synovial joint?

Answer 5

A synovial joint with more than one pair of articular surfaces

(e.g. the elbow)

Question 6

Joint lubrication is achieved by which three things?

Answer 6

1. Interstitial fluid - from cartilage
2. Hyaluronic acid (mucin) - derived from the synovium
3. Lubricin (a glycoprotein) - derived from the synovium

Question 7

Why does synovial fluid have a high viscosity?

Answer 7

Hyaluronic acid (mucin)

Question 8

The synovial fluid is a constant pool.

True or false?

Answer 8

False

The synovial fluid is continously removed and replenished via the synovial membrane

Question 9

Which two properties of synovial fluid change during movement?

Answer 9

1. Elasticity
2. Viscosity

e.g. during rapid movement, elasticity increases and viscosity decreases

Question 10

Describe normal synovial fluid properties

Answer 10

• Normally around 3.5ml present (in knee)
• Clear and colourless
• <200 WBCs
• High viscosity

Question 11

If synovial fluid is opaque what does this suggest?

Answer 11

The synovial fluid is septic

Question 12

High white cell counts in the synovial fluid may suggest which two things?

Answer 12

1. There is an inflammatory process (e.g. arthritis)
2. The synovial fluid has become septic (e.g. infective arthritis)

Question 13

Synovial joints are known by which other name?

Answer 13

Diarthrosis

Which means two articulations.

Arthritis - inflammation of articulation

Question 14

What is the main purpose(s) of articular cartilage?

Answer 14

• Provides a smooth surface with low friction to prevent wear and tear
• Distributes contact pressure over a larger surface area

Question 15

Hyaline cartilage, the cartilage type usually associated with articulation, is composed mainly of which three components?

Answer 15

1. Water
2. Type II collagen
3. Proteoglycans

Question 16

The extracellular matrix of the cartilage comprised what percentage of total cartilage volume?

Answer 16

98%

Question 17

Where does the articular cartilage receive nutrients and O₂ from?

Answer 17

Synovial fluid

(Articular cartilage is avascular - nutrients and O₂ diffuse from the synovial fluid into the extracellualr matrix, and chondrocytes)

Question 18

Which catabolic factors may chondrocytes secrete to break down the extracellular matrix?

Answer 18

• Tumour necrosis factor (TNF)-a
• Interleukin (IL)-1

These prevent proteoglycan synthesis

Question 19

Which anabolic factors may chondrocytes secrete in order to build up the extracellualr matrix?

Answer 19

• Tumour growth factor (TGF)-β
• Insulin-like growth factor (IGF)-1

These cause proteoglycan synthesis

Question 20

Increased levels of which two things suggest cartilage breakdown?

Answer 20

1. Serum and synovial keratin sulphate
2. Type II collagen in synovial fluid

Can give clues in diagnosis and/or act as seritity markers for osteoarthritis or rheumatoid arthritis

Question 21

In simple terms, what gives rise to rheumatolid arthritis?

Answer 21

The proliferation and inflammation of synovial cells

Question 22

An osteoarthritis knee may show which distinctive physical and histological features?

Answer 22

• Thickened capsule
• Hypertrophied synovial membrane
• Fibrillated articular cartilage
• Cyst formation
• Osteophyte formation (bony projections from joint margins)
• Sclerosis in subchondral bone

Question 23

Goutry arthritis is caused by a deposition of what?

Answer 23

Uric acid crystals

Question 24

Pseudo-gout is caused by deposition of what?

Answer 24

Calcium pyrophosphate crystals

(rhomboid shaped)