Physiology of joints

Question 1

What are the 3 main types of joint?

Answer 1

• Synovial (Diarthrosis)
• Fibrous (Synarthrosis)
• Cartilaginous (Amphiarthrosis)

Question 2

What are fibrous joints?

Answer 2

Fibrous joints are joints in which bones are united by fibrous tissue

They do not allow much or any movement

Question 3

What are the 2 two types of fibrous joint?

Answer 3

• Sutures
• Syndesmoses

Question 4

What are cartilaginous joints?

Answer 4

These are joints in which bones are united by cartilage, allowing limited movement

Question 5

What are synovial joints?

Answer 5

Synovial joints are joints in which bones are seperated by a synovial cavity, filled with synovial fluid, and are united by a fibrous capsule, along with other soft tissue structures (e.g. tendons, ligaments)

Question 6

What lines the inner surface of a synovial joint capsule?

Answer 6

The inner aspect of the fibrous capsule is lined with a synovial membrane containing synovial cells (Fibroblasts), which produce and absorb synovial fluid

Question 7

What makes up the outer surface of a synovial joint capsule?

Answer 7

Hyaline cartilage

Question 8

What is meant by a simple synovial joint?

Answer 8

One in which there are only 2 articular surfaces (E.g. MCP)

Question 9

What is meant by a compound synovial joint?

Answer 9

One in which there is more than 2 articular surfaces (E.g. knee joint)

Question 10

What are some of the functions of a joint?

Answer 10

During purposeful motion, joints provide stress distribution, confer stability and provide joint lubrication

Question 11

How do joints confer stability?

Answer 11

They confer stability via forming the shape of the articular component, providing ligaments for stability and forming synovial fluid, which acts as an adhesive seal that freely permits sliding motion between surfaces

Question 12

What are the main 2 lubricants found in synovial fluid?

Answer 12

• Synovium-derived hyaluronic acid (Mucin)
• Synovium-derived lubricin

Question 13

How does synovial fluid change during movement?

Answer 13

During movement, synovial fluid can change in viscosity and elasticity

Rapid movement is associated with decreased viscosity and increased elasticity

Question 14

What can cause red synovial fluid?

Answer 14

Haemorrhage arthritis
Traumatic synovial tap

Question 15

What will cause straw coloured or yellow synovial fluid with a low viscosity?

Answer 15

Inflammatory conditions

Question 16

What will cause opaque synovial fluid?

Answer 16

Septic conditions

Question 17

What is the function of articular cartilage?

Answer 17

The articular (hyaline) cartilage of the synovial joint provides a low friction, lubricated gliding surface, helping to prevent wear and tear

Question 18

What are the 4 main zones of articular cartilage?

Answer 18

• Superficial zone
• Middle zone
• Deep zone
• Calcified bone

Question 19

What is the composition of the ECM of articular cartilage?

Answer 19

Water (70%)
Mainly type II collagen (20%)
Proteoglycans (10%)

Question 20

Where is most of the water in the articular cartilage found?

Answer 20

Superficial zone (80%)

Question 21

How does the composition of articular cartilage change with age?

Answer 21

Water content and cartilage content decrease with age, decreasing stability of architecture and decreasing tensile strength

Question 22

How is the ECM of articular cartilage broken down?

Answer 22

The ECM of the cartilage is broken down mostly by the stimulation of proteolytic enzymes and inhibition of proteoglycan synthesis

This is performed by tumour necrosis factor a (TNFa) and interleukin-1 (IL-1)

Question 23

How is ECM built up in articular cartilage?

Answer 23

The ECM is built up by the stimulation of proteoglycan synthesis and counteraction of the effects of IL-1

This is performed by tumour growth factor ß (TGFß) and insulin-like growth factor 1 (IGF-1)