When you lower down into squat pose (malasana) in yoga, do your knees make a popping sound? When you lift your leg toward your chest, does your hip sometimes make a clicking or “snapping” noise? What do joint sounds like this mean? Are they dangerous?
As of late, many yoga teachers seem to have taken a fearful turn with regard to joint noises. We often hear the claim that sounds emanating from joints are an indication of a significant dysfunction in the body such as weakness, instability, or tightness. We are cautioned that we should take immediate action to remedy these dysfunctions, or else we will face negative consequences such as joint degeneration and eventual joint replacement surgery in the future.
Now we all want our joints to stay healthy and move well for us as long as possible. This is a major focus of the yoga and movement classes that I offer, so I’m always interested in any information about the body that can help me guide my students toward increased joint health and longevity.
However, it turns out that the scientific literature on joint noise such as knee popping and hip snapping is clear. If you experience a joint noise that is accompanied by pain, swelling, or an acute injury, you should see a medical professional to have the joint evaluated. However, if your joint noise is pain-free and asymptomatic (which the vast majority of bodily joint noises are), there is no reason for concern.
DEMYSTIFYING JOINT NOISES
Joint noises are actually a normal, natural by-product of movement. The catch-all medical term for all of the interesting sounds that joints can emanate is crepitus. Examples of joint crepitus include clicking, popping, snapping, clunking, and more. The exact mechanism for the noise we hear when a joint clicks or pops is still not known, but some common explanations include anatomical structures coming into contact with each other, and the formation or collapse of air bubbles within joint cavities [Ref], [Ref].
Joint crepitus is more prevalent and obvious to hear in some bodies and than in others, but despite the fearful messages that we commonly hear about them in the yoga world, these noises on their own (i.e. unaccompanied by pain, swelling, or injury) are simply a normal physiological phenomenon that are nothing to be concerned about.
A CLOSER LOOK AT KNEES
It’s common for people’s knees to click and pop when they flex and extend them - thus those knee pops we often hear when students lower into their squat (malasana) poses in yoga class. Many people believe that these noises are a sign that their knee joints are “wearing away”, that their bodies are prematurely aging, or that they have arthritis. But did you know that in a cohort of 250 subjects with normal, pain-free knees, 99% of them had knees that made noise? [Ref]. This is how prevalent, normal, and benign knee noises are. Yes, some arthritic knees can have joint crepitus - but so do most healthy knees. No definitive link between joint noise and joint pathology has been demonstrated by research [Ref].
In fact, in this same study I mentioned above, the remarkable suggestion is made that knees that make noise are actually healthier than knees that do not. I’ll give you a moment to pause and absorb this thought, because it is the complete opposite of the cautions we usually hear. Knees that make noise might be healthier than knees that don’t. It’s true!
Without going too far into the details, the basic idea is that there is one type of knee sound that specifically happens in joints that are mobile and well-lubricated. As a knee becomes arthritic and starts to lose mobility, this type of crepitus actually decreases. So when this sound is absent, it can be a sign of an unhealthy joint with arthritis and decreased joint lubrication - not the other way around!
Therefore despite popular thought, noisy knees are normal and very common. And rather than being associated with joint degeneration and dysfunction, research suggests that knee crepitus is actually associated with healthy knees!
A CLOSER LOOK AT THE HIPS
Hips that click, pop, and snap when they move are another joint noise we are often taught to worry about in the yoga world. This noise is commonly the result of either the psoas tendon moving across a bony prominence on the front of the pelvis, or the iliotibial band moving over the greater trochanter of the femur.
Although this type of hip noise is often claimed by yoga teachers to mean that one has a dysfunctional, unstable, or problematic hip that should be addressed, the scientific literature actually points to the same conclusion I mentioned in the beginning of this piece: if a snapping, popping, hip is accompanied by pain, seeing a medical professional is certainly advised. (The issue is generally resolved through conservative treatment, which is great!) But if the hip noise is pain-free and asymptomatic (as most hip noises are), there is nothing to be concerned about. Here are a few quotes I pulled from the scientific literature on this topic:
“When pain is not present [with snapping hip], treatment is not warranted” [Snapping Hip Syndrome (Musick 2017)].
“[Snapping hip is] a common asymptomatic condition which may occur in up to 10% of the general population” [Endoscopic Release of Internal Snapping Hip: A Literature Review (Via et al 2016)].
And my personal favorite: “Snapping caused by the iliopsoas tendon… is a common incidental observation that often requires little treatment on the part of the clinician other than assurance to the patient that this finding is not a harbinger of future problems” [Evaluation and Management of the Snapping Iliopsoas Tendon (Byrd 2006)].
This serves as further evidence that audible joint noises are normal, and are not a necessarily a sign of dysfunction in the body.
THE MOST CLASSIC EXAMPLE: KNUCKLE CRACKING
Perhaps knee and hip noises don’t warrant concern if they are pain-free, but what about the sounds associated with knuckle cracking? We are probably all familiar with the caution that cracking your knuckles will give you arthritis later on in life. But it turns out that this warning is unsubstantiated as well.
We knew this as far back as 1975, when a study conducted found no correlation between knuckle-cracking and arthritis. A quote from this paper reads: “The data fail to support evidence that knuckle cracking leads to degenerative changes in the metacarpal phalangeal joints in old age. The chief morbid consequence of knuckle cracking would appear to be its annoying effect on the observer.” [Ref]
Additionally, a more recent study on knuckle cracking from 1990 looked at 300 subjects and compared those who did and did not habitually crack their knuckles. It found that “there was no increased preponderance of arthritis of the hand in either group” [Ref].
WORRY AND FEAR-AVOIDANCE OF BENIGN BODY NOISES
As we can see, the evidence about joint noises is clear: if they’re accompanied by pain, swelling, or injury, you should see a medical professional for an evaluation. But if they are asymptomatic and pain-free, there is no need to worry about them.
In reality, the human body is not a perfectly silent organism. Our insides naturally make noises due to normal physiological processes. Think about the sounds we sometimes hear when we are digesting our food, or the sound of our heartbeat when we’re exercising. Joint noises are simply another form of sound that can be a by-product of movement.
Rather than encouraging worry and catastrophizing, we should see asymptomatic joint noises as a normal part of healthy movement. When we teach people that certain movements and joint sounds are inherently worrisome, this can encourage fear-avoidance behavior and a reduction in movement, which have their own negative consequences and can ironically contribute to pain.
As physiotherapist Clare Robertson writes in her excellent paper titled Joint Crepitus - Are We Failing Our Patients?:
“To accurately inform and reduce anxiety is likely to empower patients and reduce their risk of catastrophizing... It is well documented that there is a clear link between catastrophizing and long-term poor outcome within musculoskeletal medicine.” [Ref]
P.S. If you find the topic of joint crepitus interesting, you might enjoy this short video from Physiotutors, a source for evidence-based physiotherapy education: