Cavitation

Snapping hips, crackling knees, popping knuckles…all part of the human experience. Fully decoding these noisy joints may never come to pass for the technology required to glean such knowledge is for now, out of reach… Just kidding! Modern science knows exactly what these are and why these happen. Put on your safety belts and keep all hands, arms, feet, and legs in the blog at all times, because we’re about to adventure into the realm of cavitation: cracking and popping!

The Language

As a chiropractor, I hear “cracking” all the time and get loads of questions about the what and why of it all. The first thing I usually touch on, however, is the necessary language used to describe these noises. Cracks, pops, snaps – all of these describe the sound.

What’s more important is the feeling behind them. Does it feel like something is flipping over something else? Is there just a sticky spot you push past and feel a pop? You can imagine a cracking sound being very different than a cracking feeling… one is certainly more innocuous than the other.

To further the point, you never really want to describe a bone as cracking, but rather, a joint making a cracking sound, which is certainly within the realm of normal. Ultimately these sounds fall into one of two categorical phenomena which we’ll describe as either cavitation or tension adjustment.

Cavitation: THE WHAT

When a rapid pressure change happens for a fluid, little baby bubbles form and spontaneously pop, causing a crisp popping sound. Think of opening a can of soda – the carbonation immediately gets to escape from the liquid. Many of our joints have a similar action that occurs within our synovial joints – certain movements or forces can cause the joint to experience a brief instance of negative pressure, causing tiny nitrogen bubbles to form and spontaneously dissolve in a spectacle of sound! Cavitation!

This is the main thought behind why chiropractic adjustments make sound (which are just Grade V manipulations and requiring a license to perform on others). Cracking your knuckles yields the same sort of action. Other explanations of similar sounds include a suction-cup like action between joint surfaces – imagine pulling a plunger off a wet surface. Bodies are cool, huh?

Cavitation: THE GOOD, BAD, UGLY

A cavitation in a joint is usually followed by relief. The joint is usually a little sticky to begin with and the action of popping said joint can immediately restore range of motion. Again – to do this on someone else usually requires a license because you don’t want to be forcing joints into unhealthy ranges of motion, or accidentally causing someone’s back to go into spasm by trying to adjust it when it didn’t need one.

Knuckles, by contrast, are fairly innocuous. Numerous studies have failed to find any ill effects from cracking knuckles compared with control groups, so don’t think for a second that cavitations will lead you down the path to arthritis! In fact, Harvard has done exhaustive studies on this and they always come up empty-handed. The stigma behind the knuckle-cracking was powerful, and throughout the ages, conclusions in studies have ranged from “Just to be careful, don’t do it!” to today’s firm stance that there’s nothing to fear whatsoever.

Here’s my more nuanced approach: Joints like moving, but forcing joints into certain ROMs can definitely be a bad idea for joint health, both long and short term. If you need to get a cavitation out of your knuckles, I’d rather have you traction them along the long axis rather than forcing them into flexion or extension to “crack” them. Too much flexion or extension can create laxity in the capsule, and you’ll find yourself feeling like you need to crack them every 20 min or so.

Pulling: Yas. Pushing: Nah.

Tension Adjustment: THE WHAT

As we all know, our body is a tension system. Nobody puts it better than Thomas Myers, world-renowned anatomist and cartographer of the wildly popular Anatomy Trains paradigm: we’re just an assortment of bones with an intricate “tensegrity” unit of myofascia, ligament, and tendon. Our long tendons are often coursing around multiple 90 degree angles and held down by transverse ligaments and retinaculum, all to enable us to have control over our amazing joint range of motion.

I like to describe this anatomical problem-solving by conjuring images of asparagus held together by a simple few rubber bands. These rubber bands in our bodies are a large source for adhesion; they can get irritated and build up scar tissue, which makes it tougher for our tendons to glide through.

Thusly, we have a breakdown of the tension system, and these tendons have to get creative about getting where they need to go. The IT band is a perfect example (or literally anything in the ankle). The distal part of the IT band has to cross over the lateral femoral condyle, but if it has to play tug-of-war with other structures, it ends of rubbing really nicely against that condyle, creating a snapping effect!  A similar effect is noted when kneeling down and your ankles or knees pop. It’s usually just tendons or other bands of soft tissue snapping into place because they’re just too tight.

Tension Adjustment: THE GOOD, BAD, UGLY

Best advice by Docs:  if it doesn’t hurt when it pops/snaps/cracks, don’t worry about it! That’s big-picture stuff. You know, a medical necessity-focused response. For me, in these scenarios I see a tension system building up more adhesion and tension bit by bit. If we focus on where those clicks and pops are coming from, we can identify and mobilize these structures so the tension system regains integrity – at least enough for those structures not have to play tug-of-war with their neighboring tissues.

Shoulder, ankle, knee, hip – none of that clicking usually needs to happen in a relatively healthy human. But again, it’s not a huge life-impacting problem. As stated near the top, all part of the human experience as we go through life exposed to and accumulating stress. But there can be situations where constant tension adjustments are more problematic.

Repetitive stress injuries (RSI) often are an example of what happens when there’s too much rubbing/snapping/popping – the tissues get real raw without time to heal and that’s where pain/dysfunction starts to develop. A great way to address this yourself is with the Functional Range Conditioning system, as is utilized in Kinstretch, which breaks down movement in a calculated way to isolate optimal mobility in some of our favorite joints. Or just try your favorite mobility drills!

My stance – if a mobility exercise isn’t working after a few tries, try something else.

The Sounds You DPOPS, GRINDING, CLUNKING 

A few noises and feelings can certainly be linked to other issues. For instance, a quick turn on a basketball court accompanied by a “pop” and an unstable feeling or black-out pain usually indicates a tendon or ligament has been torn. Most likely you’ll know to go see someone.

Same thing with “clunk” sounds – usually a joint is relocating, most likely meaning that joint is unstable. Definitely double-check with a doc if your body is clunking around. Grinding feelings can often be crepitus or scar tissue within the myofascial system, but at its worst, it can be a joint grinding against another joint which is never a great thing.

Luckily there are great manual therapists out there and rehab specialists that have made their careers around helping these issues! Graston/IASTM, Cupping, ART/MRT, Massage, or Rehab Exercise are all great ideas to refer out for if necessary to help augment your training.