TWIL #067 - Cartilage Has No Blood Supply - Which Is Why It Never Heals
Cartilage contains no blood vessels, no nerves, and no lymphatics. Nutrients reach it by diffusion alone. When it is damaged, the body has almost no mechanism to repair it.
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Cartilage is a specialised connective tissue that covers the ends of bones at joints, forms the flexible parts of your ears and nose, and supports structures like the trachea and intervertebral discs. It is extremely tough and slightly elastic. It is also, from a healing standpoint, nearly inert.
Why cartilage cannot heal:
Most tissues heal because blood vessels deliver oxygen, nutrients, immune cells, and the growth factors needed to rebuild damaged tissue. Cartilage is avascular - it contains no blood vessels at all. It is also aneural (no nerves) and alymphatic (no lymphatic vessels).
Nutrients and oxygen reach chondrocytes (cartilage cells) by diffusion through the surrounding matrix - a slow process adequate for maintenance but not for repair. When cartilage is damaged, the chondrocytes in the area cannot proliferate fast enough or receive adequate resources to regenerate the lost tissue.
The body's repair response to cartilage damage typically produces fibrocartilage - a lower-quality, less elastic tissue that wears out faster than the original hyaline cartilage it replaces. This is why osteoarthritis, in which cartilage degrades gradually, has no good biological repair pathway and is ultimately managed rather than cured.
Why knee cartilage damage is so significant: The articular cartilage in the knee joint is subjected to high loads and is among the most stressed cartilage in the body. A damaged meniscus or articular surface begins a progressive cycle: uneven load distribution leads to further wear, which produces inflammation, which accelerates degradation. The absence of a vascular repair mechanism means the window for recovery is narrow and the damage tends to accumulate.
Current research: Approaches being explored include:
- Microfracture surgery: deliberately breaking the underlying bone to allow bone marrow cells (which can differentiate into cartilage-like cells) to bleed into the defect
- Stem cell injection: delivering mesenchymal stem cells capable of producing cartilage matrix
- Tissue engineering: growing cartilage in vitro and implanting it - experimental but showing promise in clinical trials