Human knee cartilage cannot heal itself after an injury

While a broken bone can knit itself back together in weeks, the pearly white tissue known as articular cartilage is functionally frozen in time. Because it lacks blood vessels and nerves, it cannot signal for the nutrients or specialized cells required for self-repair. Once a tear develops, the joint begins a slow, irreversible decline toward arthritis. For decades, surgeons attempted to fix this by drilling tiny holes into the bone to trigger bleeding, but the resulting scar tissue was a weak substitute that lacked the durability of the original material.