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Comment by catalogia | Hacker News Reader

I've suspected that cartilage regenerates ever since I learned that long term knuckle cracking doesn't cause long term damage, despite the audible crack coming from cavitation (which can be very destructive to things like ship propellers, eroding the metal over time.)

If it didn't, my hands would probably be crippled by now.

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I thought it was known that cartilage can regrow but it's just at such an incredibly slow pace due to lack of circulation that you can effectively say it doesn't grow?

Edit: after some googling I found this result

> age 15 or 16 would be about the average age for bones to stop growing, so from that point on, there is no collagen regeneration in the cartilage. Your body, on its own, cannot regenerate the cartilage it loses in its adult years.

https://regenexx.com/blog/does-cartilage-heal-on-its-own/

That source is over simplifying; some bones and cartlidge are known to continue growing in adults - the jaw and ear lobes for example.

That does sound weird considering how many athletes develop issues later in life due to build up of cartilage. My friend, 66, for example did boxing in his late 20's and started getting issues in his 50's due to nasal-blockages, to the point where he now needs to drill away some of the cartilage to get rid of migraines and such..

Cauliflower ears in rugby players would be another example.

Cauliflower ears are caused by the ear cartilage dying off and being replaced by fibrous scar tissue. That's definitely not cartilage overgrowth.

True hyaline cartilage cannot "build up." The good stuff (intra articular) is a precious resource that you can only lose, not gain.

The cartilage in your nose and ear are different, and besides, the stuff that's blocking your boxer friend's nose, and causing cauliflower ear is not really cartilage. It's fibrous growth which has a blood supply. It's your body trying to replace real cartilage with a poor substitute.

Exactly, not all cartilage is the same. The good stuff doesn't come back unfortunately.

They're selling a product that depends on you not knowing the truth. Medical hucksters routinely lie with facts.

I learned a little about this topic recently after a bad knee injury from running [torn meniscus] --

Blood supply does have a lot to do with healing-or-not -- taking the meniscus as an example, about 30% of the meniscus has a blood supply, the rest does not, so that if the injured part is of that 30%, it can actually heal, whereas if not, they can only clean it up and stitch it together like a rag doll ---

[for the curious : I got lucky and my injury healed tolerably well on its own sans surgery]

I believe the prevailing thought on the audible cracking is that it is the bubbles in the fluid between cartilage and nothing to do with the cartilage itself.

That's my understanding. But the collapsing bubbles are next to the cartilage I believe, and it seems to me should therefore be causing cavitation erosion. When cavitation erodes a boat's propeller, the cavitation is occurring in the water next to the propeller, not in the propeller itself.

https://en.wikipedia.org/wiki/Cavitation#Cavitation_damage

Here's a video of it happening on live x-ray:

https://www.youtube.com/watch?v=ZyUjH2FmRLE

Quite creepy

Does knuckle cracking have anything to do with cartilage? I suspect it is not a related process.

https://www.medicalnewstoday.com/articles/259603.php

The cracking sound is caused by nitrogen bubbles, not by cartilage breaking. Cracking your knuckles is safe as far as we know, if anything it probably helps because you're stretching your ligaments.

Doc told me your tendons can end up taking up the slack, which can cause other issues

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