05/29/2023
Treatment of Periosteal fascia for end plates of the bones help cartilage blood supply
Zones of Articular Cartilage: Analysis by Physio Meets Science
“Articular cartilage is a unique, specialized tissue that, in a healthy state, allows nearly frictionless movement across its surface. Its structure and mechanical properties allow decades of repetitive loading forces, despite a limited capacity for repair. No artificial material has been able to replicate these properties. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3445147/, https://pubmed.ncbi.nlm.nih.gov/28577703/
👉 Most articular cartilage is approximately 2–4 mm thick (https://pubmed.ncbi.nlm.nih.gov/10343537/, https://pubmed.ncbi.nlm.nih.gov/10355554/), while the patellar articular cartilage is between 7 and 8 mm thick (https://pubmed.ncbi.nlm.nih.gov/10367018//). Grossly, articular cartilage is comprised of cells (chondrocytes), matrix (fibers) and extracellular matrix.
👉 Articular cartilage's four layers or zones (superficial, transitional, deep and calcified) are distinguished by the shape and orientation of the chondrocytes, and the distribution of type II collagen (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3445147/, https://pubmed.ncbi.nlm.nih.gov/25783021/) (Fig. layers of articular cartilage).
👉 The superficial or tangential zone is the outermost surface that is designed to resist forces from arthrokinematic roll, spin and glide (https://pubmed.ncbi.nlm.nih.gov/9785256/). The superficial zone has the highest collagen and water content. This layer contains elongated chondrocytes with fibers resting parallel to the surface. This orientation, along with its covering called the lamina splendens, optimizes resistance to shear forces (https://pubmed.ncbi.nlm.nih.gov/7919525/, https://pubmed.ncbi.nlm.nih.gov/9785257/).
👉 While this zone is the most cell and fiber-rich of all layers, the chondrocytes are relatively metabolically inactive making repairs to this outermost layer difficult (https://pubmed.ncbi.nlm.nih.gov/9785257/, https://pubmed.ncbi.nlm.nih.gov/25783021/). Therefore, any injury or degenerative process that damages this protective surface will expose the underlying layers to shear forces. The adult who sustains a chondral injury may have difficulty healing due to loss of this protective layer.
👉 As its name implies, the transitional zone is a transition point between the highly specialized superficial and deep zones The transitional, or middle zone contains fibers of a larger diameter that are more randomly dispersed along with chondrocytes which contain more metabolically active intracellular components (i.e. endoplasmic reticulum, mitochondria, Golgi membranes) suggesting a stronger repair capability Functionally, the middle zone is the first line of resistance to compressive forces. (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3445147/)
👉 Below the transitional zone is the deep, or radial zone containing fibers that are larger than the previous two layers. Chondrocytes are oriented vertically relative to the underlying bone and articular surface, and similarly, fibers are perpendicular to the articular surface. Proteoglycan content is highest and water content the lowest in this zone (https://link.springer.com/chapter/10.1007/978-3-030-01491-9_1). Unlike the superficial layer which is designed to resist shear forces, the lower layers, with their vertical orientation and high proteoglycan content, are ideally suited to resist compressive and tensile forces.
👉 Separating the radial zone from the subchondral bone, or calcified zone, is the tidemark. The tidemark delineates the source of nutrition in the adult articular cartilage. Above the tidemark, nutrition is provided by diffusion from the synovial fluid; below, nutrition is supplied by the underlying vascular supply from the subchondral bone. Experimental evidence from animal models has shown that immature cartilage can be nourished in both ways, but in mature animals, the predominant source is synovial fluid due to the dense calcified barrier of subchondral bone that could limit the diffusion of fluid and soluble substances through the vascular channels (https://pubmed.ncbi.nlm.nih.gov/23109140/, https://pubmed.ncbi.nlm.nih.gov/22850529/).
Subchondral mechanism has been debated (https://pubmed.ncbi.nlm.nih.gov/2081697/, https://pubmed.ncbi.nlm.nih.gov/11069733/); however, it has been reported that subchondral bone’s blood vessels may expand and pe*****te the adjacent calcified cartilage through channels and the nutrients may reach the cartilage through these perforations. This theory supports the importance of this pathway for cartilage nourishment. It was postulated that 50% of glucose requirements, oxygen and water are given by perfusion from subchondral vessels (https://pubmed.ncbi.nlm.nih.gov/20119671/, https://pubmed.ncbi.nlm.nih.gov/10565710/).
Illustration: https://link.springer.com/chapter/10.1007/978-1-4939-1673-3_10
