Ok… so today we are going to talk about cartilage. As I mentioned previously, it is an amazing substance and has some unique properties which allow our joints to function in they do.
What is cartilage?
Cartilage is the tough white slippery coating that covers the ends of all bones within a human (and mammalian) diarthrodial joint. There are different types of cartlage (hyaline / elastic / fibrous) but the one that’s of interest to us is hyaline cartilage.
We’re born with it and the human foetal skeleton starts life a cartilage model which slowly ossifies with time to form the bony skeleton. In this skeleton, the ends of the bones within the joints are covered in hyaline cartilage.
Its main function is to allow smooth, frictionless movement for a joint and to transmit the huge forces that can be generated, to the underlying bone without causing pain. This is particularly important in weight bearing joints like the knee, hip and ankle.
Cartilage has no blood supply, no nerve supply and no lymphatics which makes it an incredibly unique human tissue. This means that it doesn’t feel pressure or pain, which is exactly what’s needed but on the flip side doesn’t follow the same rules of tissue healing i.e. due to the lack of blood supply, it can’t heal. This is a problem!
Cartilage is mostly made of water 70-80% and matrix which is the stuff that holds the water and other components. There are cells called chondrocytes, type II collagen, GAGs (glycosaminoglycans), chondroitin and hyaluronic acid. The cells are arranged in a way that allows the cartilage to resist shear forces (see zone I / surface layer) and also to resist compression (see zone IV).
The cartilage receives its nutrition from the joint fluid (synovial fluid) and this is from a process of diffusion of water and nutrients through movement of the joint. Which is why it’s so important to keep moving and exercising!
Unfortunately, cartilage can get injured (chondral lesion) and also generally deteriorates with age (osteoarthritis). These are common problems in orthopaedic surgery and are great topics for the next blog!
Thanks for reading and do get in touch if you have any questions.