Joint Histology Flashcards
Name the layers of a joint
- tangential zone
- transitional zone
- radial zone
- tidal zone (tide mark)
- calcified zone
- subchondral bone plate
What zone of a joint is also called the “skin of cartilage, or the “armor plate”?
tangential zone
What is the tangential zone comprised of?
- flat chondrocytes
- lots of type 2 collagen
What event would guarantee accelerated degeneration of a joint and why?
- Fx through articular surface
- violates armor plate
What is the transitional zone of a joint comprised of?
- chondrocytes
- lots of matrix
What are the functions of the transitional zone of a joint?
“day-to-day” functions
- shock absorption
- maintain superficial layer
In what joint layer does the most growth occur?
radial zone
What is the radial zone comprised of?
columns/striations of chondrocytes like in articular cartilage
What separates the vascular from avascular regions of a joint?
tidal zone (tide mark)
What joint layers receive nutrients from diffusion?
- tangential zone
- transitional zone
- radial zone
What joint layers receive nutrients from blood supply?
- tidal zone
- calcified zone
- subchondral bone plate
What joint layer is also called the “blue line”
tidal zone
(stains blue with H&E)
What is the calcified zone of a joint comprised of?
- small chondrocytes
- heavy calcification of matrix
What joint layer sees more chondrocyte reproduction in disease states such as Acromegaly?
calcified zone
The calcified zone is the transition from the ____ to the ____
articular surface
subchondral bone
What joint layer is visualized as the cortical line radiographically?
subchondral bone plate
What is the function of the subchondral bone plate?
supports articular cartilage
What layer of a joint do blood vessels enter into?
subchondral bone plate
Describe the layering and orientation of collagen
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
Describe the orientation of collagen and chondrocytes in the radial zone of a joint, and how this affects the integrity
- run in same direction as growing chondrocytes pull collagen
- creates point of weakness due to shearing forces between layers
Why is nutrient diffusion of articular cartilage poor in patients with degenerative changes?
- thinner cartilage = ^force on bone
- Wolf’s law -> ^thickness of subchondral plate
- pulls tide mark down = poor diffusion (vascular supply is further away)
What is the interface between mineralized and unmineralized cartilage of a joint?
tide mark (blue line)
The articular side of the tide mark receives nutrients via ____
diffusion
The osseous side of the tide mark receives nutrients via ____
epiphyseal blood vessels
What do chondrocytes above the tide mark do?
replicate and migrate up towards surface above line
What do chondrocytes below the tide mark do?
will divide only if there is the appropriate chemical stimulus (eg. Acromegaly)
