"The surfaces of the knee joint can be thought of as being a bit like a Crunchie bar --- the deeper bone is like a honeycomb that has a very rich blood supply and which is full of bone marrow and stem cells. However, this is covered by a hard egg-shell like cortex of bone, called the subchondral bone plate, which acts as a barrier. The articular cartilage is like the chocolate layer on the surface of the Crunchie bar, but the hard layer of bone underneath acts as a barrier, and unfortunately the articular cartilage itself has no blood supply."
"The cartilage is like the lubricant in an engine, allowing for smooth mobility and flexibility in the joint and preventing painful bone-on-bone contact. And once the thin coating is damaged it can be difficult and often impossible to repair."
"Cartilage is like a sponge – it needs fluid to function properly. This means not just water (although that's 70% of the cell structure) but fluids like hyaluronic acid, a natural substance our body produces to "grease" the joint during movement."
"In addition, mature cartilage cells are like nerve cells in that they do not divide. This means that they do not self repair and do not propagate."
"The analogy I give my patients is that cartilage cells are like bricks without the mason. Since they are cells that are alive, they have some limited ability to rearrange and maintain themselves as well as produce their own mortar (called ECM), but they can't do much complex repair without a brick mason."
"Microfracture is aimed at fixing the articular cartilage that covers the surface of your bones, much like enamel on teeth. The cartilage of a knee joint is like a bar of soap. Every time that soap is used, the bar gets a little smaller. The harder you scrub, the more the soap erodes "
METAMIA is a free database of analogy and metaphor. Anyone can contribute or search. The subject matter can be anything. Science is popular, but poetry is encouraged. The goal is to integrate our fluid muses with the stark literalism of a relational database. Metamia is like a girdle for your muses, a cognitive girdle.