Joint Histology

Question 1

Name the layers of a joint

Answer 1

• tangential zone
• transitional zone
• radial zone
• tidal zone (tide mark)
• calcified zone
• subchondral bone plate

Question 2

What zone of a joint is also called the “skin of cartilage, or the “armor plate”?

Answer 2

tangential zone

Question 3

What is the tangential zone comprised of?

Answer 3

• flat chondrocytes
• lots of type 2 collagen

Question 4

What event would guarantee accelerated degeneration of a joint and why?

Answer 4

• Fx through articular surface
• violates armor plate

Question 5

What is the transitional zone of a joint comprised of?

Answer 5

• chondrocytes
• lots of matrix

Question 6

What are the functions of the transitional zone of a joint?

Answer 6

“day-to-day” functions
- shock absorption
- maintain superficial layer

Question 7

In what joint layer does the most growth occur?

Answer 7

radial zone

Question 8

What is the radial zone comprised of?

Answer 8

columns/striations of chondrocytes like in articular cartilage

Question 9

What separates the vascular from avascular regions of a joint?

Answer 9

tidal zone (tide mark)

Question 10

What joint layers receive nutrients from diffusion?

Answer 10

• tangential zone
• transitional zone
• radial zone

Question 11

What joint layers receive nutrients from blood supply?

Answer 11

• tidal zone
• calcified zone
• subchondral bone plate

Question 12

What joint layer is also called the “blue line”

Answer 12

tidal zone
(stains blue with H&E)

Question 13

What is the calcified zone of a joint comprised of?

Answer 13

• small chondrocytes
• heavy calcification of matrix

Question 14

What joint layer sees more chondrocyte reproduction in disease states such as Acromegaly?

Answer 14

calcified zone

Question 15

The calcified zone is the transition from the ____ to the ____

Answer 15

articular surface
subchondral bone

Question 16

What joint layer is visualized as the cortical line radiographically?

Answer 16

subchondral bone plate

Question 17

What is the function of the subchondral bone plate?

Answer 17

supports articular cartilage

Question 18

What layer of a joint do blood vessels enter into?

Answer 18

subchondral bone plate

Question 19

Describe the layering and orientation of collagen

Answer 19

collagen layers have opposing grain directions allowing resistance to forces from different directions
- superficially: mostly parallel to jt surface
- middle/deeper: more random
- radial: perpendicular to jt surface

Question 20

Describe the orientation of collagen and chondrocytes in the radial zone of a joint, and how this affects the integrity

Answer 20

• run in same direction as growing chondrocytes pull collagen
• creates point of weakness due to shearing forces between layers

Question 21

Why is nutrient diffusion of articular cartilage poor in patients with degenerative changes?

Answer 21

• thinner cartilage = ^force on bone
• Wolf’s law -> ^thickness of subchondral plate
• pulls tide mark down = poor diffusion (vascular supply is further away)

Question 22

What is the interface between mineralized and unmineralized cartilage of a joint?

Answer 22

tide mark (blue line)

Question 23

The articular side of the tide mark receives nutrients via ____

Answer 23

diffusion

Question 24

The osseous side of the tide mark receives nutrients via ____

Answer 24

epiphyseal blood vessels

Question 25

What do chondrocytes above the tide mark do?

Answer 25

replicate and migrate up towards surface above line

Question 26

What do chondrocytes below the tide mark do?

Answer 26

will divide only if there is the appropriate chemical stimulus (eg. Acromegaly)