cartilage
Meaning of cartilage: No blood supply and no nerves: cartilage neither heals well nor hurts directly, so joint pain comes from the structures around it.
Definition of cartilage
Cartilage is a firm, flexible connective tissue made of scattered cells embedded in a dense gel of collagen and other fibers. It carries load and holds shape while bending far more than bone, and it contains no blood vessels and no nerves of its own. Its cells are fed by fluid seeping in from the surface, which is why cartilage repairs so poorly.
What are the three types?
| Type | Where it is found | What it is built for |
|---|---|---|
| Hyaline | The ends of bones inside joints, the nose, the windpipe and the voice box | A smooth, low-friction sliding surface and a springy tube that stays open |
| Elastic | The outer ear and the epiglottis | Holding a shape while springing back after being bent |
| Fibrocartilage | The discs between vertebrae and the menisci of the knee | Absorbing compression and resisting pulling forces |
All three are connective tissue built on the same plan, and what separates them is the mix of fibers in the gel. Hyaline cartilage is the most widespread and the type meant when a report describes thinning inside a joint. In the larynx and the airway below it, hyaline cartilage forms rings and plates that keep the tube from collapsing during the pressure swings of breathing, and several of those pieces stiffen with age as calcium is laid down in them.
Why does it heal so slowly?
Every other tissue repairs with the help of blood, which brings oxygen, nutrients and the cells that do the rebuilding. Cartilage has none. Nourishment reaches it only by diffusion, over short distances and slowly, and inside a joint that diffusion depends on movement squeezing fluid in and out of the surface. A tear confined to adult joint cartilage often does not close at all. When the injury cuts deeper and reaches the bone beneath, marrow cells can migrate up into the gap, but what they build is fibrocartilage, mechanically weaker than the hyaline surface it replaces. The same lack of blood supply has one advantage: cartilage taken from a person's own ear or rib survives transplantation unusually well, which is why it is favored in reconstruction.
If cartilage has no nerves, why does a worn joint hurt?
The worn surface itself sends no signal, because there is nothing in it to send one. The pain of a worn joint comes from the bone underneath, which does carry nerves and reacts to the load it is no longer shielded from, and from the joint lining, the capsule and the muscles working around an unstable joint. That separation explains a persistent puzzle: images showing severe thinning in someone with little pain, and marked pain in someone whose images look nearly normal.
Used in a sentence
Imaging of the knee showed thinning of the cartilage within the joint.
Good to know
Because cartilage has neither a blood supply nor nerves of its own, it heals considerably more slowly than most other tissue after injury and produces no pain directly, so the pain of a worn joint arises from the bone, lining and capsule around it.
Word origin
Where “cartilage” comes from
From Latin cartilago, meaning gristle.