|Articular Cartilage Zones in Normal Articular Cartilage|
is composed of hyaline cartilage. It lacks a
perichondrium and is avascular and aneural. The
function of the articular cartilage is
to provide a smooth surface for articulation and act as a shock absorber. Water in the
synovial fluid is attracted to the negatively charged proteoglycans within the articular
cartilage. Under compression some of the
water is squeezed out into the joint space, therefore maintaining this space in a
hydraulic fashion. When the pressure is
relieved, the water is reabsorbed, contributing to the resiliency of the cartilage.
1. Synovial cavity: see previous slide.
2. Lamina splendens: Outermost layer is considered the articular surface. A highly fibrous layer, with numerous collagen fibrils arranged parallel to the joint surface in order to resist tension. Hyaluronic acid cannot escape, yet glucose is able to diffuse in from the surrounding synovial fluid. This layer acts as a barrier because there is no perichondrium. Increasing gaps will appear with age.
3. Tangential Zone: Contains flatter chondrocytes and thicker fibrils running parallel to the joint surface.
4. Transitional Zone: Thickest zone, containing "typical looking" chondrocytes, which may stack towards the surface in isogenous groups. Thicker collagen fibers radiate inward, perpendicular to the surface, acting as an anchor to prohibit separation of zones.
5. Tidemark: (Ossification front) A boundary point representing a change in cartilage stiffness from transitional to calcified. This line can often be seen using light microscopy.
6. Zone of Calcified Cartilage: Includes hypertrophic chondrocytes that are still active in matrix production. These chondrocytes stain darker due to an increased mineral content in the matrix. The junction between this zone and the subchondral bone has an irregular surface to help hold them together, much like dermal papillae.
7. Subchondral Bone