The crackling noise -- which in Saving My Knees I likened to that of someone sitting on a bag of potato chips -- is called "crepitus." This medical term means a "grinding, crackling or grating sensation or sound," so says this arthritis Web site.
The site also declares, incorrectly I think, "If it occurs without any pain, it is unlikely to be caused by arthritis or any medical condition, and is usually meaningless." A popular "save your knees" book on the market also asserts that that noise from your knees, unaccompanied by pain, isn't significant. I think that's wrong thinking, and dangerous.
What if you were a ship's captain and spotted a strong beam of light through the fog? If you continued on your way without incident, you might conclude that the light was meaningless. However, if you strayed too close to the light's source -- and wrecked your ship on the rocky shores that this lighthouse was trying to warn you of -- I think you'd argue the opposite: that the light was quite meaningful indeed.
Similarly, crepitus of the knee (note: I'm talking about a certain kind of noise here, not the airy pops or harmless cracks that all joints make from time to time) is a warning that something is amiss. Before I developed knee problems, I heard (and ignored) crepitus in my joints because there was no pain (so I figured, as the writer above tells us, that it was meaningless).
Big mistake. A few months later, I was in the fight of my life to rescue a pair of burning, aching knees.
So then am I advocating that knee crepitus become an obsession as you try to recover? Nope, not that extreme either. For two big reasons:
(1) You don't have to eliminate all crepitus to have happy joints again.
My knees still crackle some, though certainly less than before. Perhaps they always will. That's okay by me, if I'm not in pain. I do, however, make a point of listening closely to the crepitus occasionally, because when it starts getting louder, I know my knees are probably going in the wrong direction.
Remember, over the age of 30, most people have cartilage defects in their knees, and probably a lot have some kind of related crepitus. (You can hear minor crepitus if you bend over a subject's knee, so your ear is just above the joint, and have that person do a leg extension.) Back when I was thinking about doing a rugged mountain climbing event on my bicycle, someone who did the climb every year (and so trained a lot on hills) reported on a forum that his knees were very noisy. But he had no pain.
(2) Monitoring crepitus smartly is really, really hard.
Readers of my book will recall that knee noise was one of the variables I tracked and scored. In retrospect though, I'm not sure how useful that was.
Because the condition of damaged cartilage changes very, very slowly, so you're not likely to find significant differences, day to day. Because the noise appears to be a function of a variety of things (such as the quality of the synovial fluid at a given instant). From my experience, these other things are quite variable over the short term in ways that aren't easy to understand.
For example, even after an easy cycling session, my knees sound crunchier than usual. If my primary objective were to eliminate all noise from my knees at all times, maybe I'd stop cycling -- which would be a bad thing.
So, in conclusion, I think crepitus associated with cartilage damage is absolutely meaningful, even if you're pain-free. Ignore it at your own peril. But should getting rid of crepitus be the be-all, end-all of a program to heal bad knees? Absolutely not, in my opinion. I would focus on getting rid of pain. Strengthening my knees. Engaging in lots of knee-friendly movement and exercise.
And, in the end, after doing all the right things and getting better, I bet you'll find the crepitus has improved along with the rest of the joint.