If you fall on the ski slopes or slip on a patch of ice, you’ll probably be better off if you break your leg than if you rip the cartilage in your knee. Unlike bones, your cartilage is never going regrow or heal, according to a new study based in part on fallout from past nuclear explosions.

“The surgeons who do joint replacements should not be afraid,” says study co-author and rheumatologist Michael Kjær of the University of Copenhagen. “They are going to be in business for some time.”

As plenty of athletes and weekend warriors can attest, damaged knee cartilage is reluctant to mend. But because measuring cartilage turnover is difficult, researchers have never been sure whether adults replace any of the material.

In some previous studies, scientists saw an increase in collagen synthesis in patients with osteoarthritis, which could represent the joint’s attempt to repair itself. But Kjær’s team didn’t detect this effect.

Although researchers have tried several approaches to induce regrowth of knee cartilage, such as inserting stem cells or slivers of healthy cartilage into the joint, they haven’t worked.

http://www.sciencemag.org/news/2016/07/why-knee-injuries-often-don-t-heal

Quite actual to bikers and such.