Snap, Crackle, Pop

Snap, Crackle, and Pop: Joint noises and their meaning

by Jarlo Ilano, M.P.T.,C.S.T.

There many types of sounds that our joint structures elicit during the various motions we engage in, whether in specific exercise, or simply getting up in the morning. Depending upon who you speak with these sounds are either to be avoided like the plague, glossed over, or sought after like the Holy Grail.

The distinct nature of the sounds, in general, also gives some insight into their physiological underpinnings. What exactly is happening when you hear a click, pop, snap, clunk, or grind?
In truth, it is very difficult to say with great accuracy what is occurring, though we can make quality inferences. Especially after examining and assessing a variety of individuals in person. Needless to say, the accuracy significantly diminishes if you are not present to both hear and feel the sounds as they are happening.

The “pop” you hear when you articulate your joints, or “crack” your knuckles is from the synovial fluid transforming into gas in the joint capsule. A joint capsule surrounds all synovial joints and is a “closed” system filled with fluid, so any deformation would cause a change in pressure. The fluid changes state, as the capsule is distended. This is why you cannot crack your knuckles immediately after you have cracked them. It’s been said that it takes about 20 minutes for the gas to resorb. For those sounds that emanate repeatedly with a certain motion, it would appear that they are not a result of this mechanism.

As for other sounds? This is where we can go awry. Debate from many perspectives can be very difficult to wade through, however here are some of my interpretations. Repetitive “clicks” could be connective tissue out of its proper alignment or cartilaginous tissue damage such as torn meniscal flaps or other impairment. Crepitus, or crunching, is most likely chondral tissue damage as well. The specific tissue at hand is easily debatable. Another sound, more like a “rip”, can often be heard or felt as well. This is scar tissue, and depending on the situation it can be beneficial or problematic.

The “clunk” is an interesting phenomenon. Often felt as a shift, and which may or may not accompany the louder “pop”, it is generally acknowledged as a distinct entity. This may be a true subluxation, in which the joint is “off axis”, and a particular movement shifts it back on axis. This is far from unequivocal, but I think there is merit for this particularly in the wrists, ankle, sacrum, low lumbar and mid cervical spines. These sounds occur in what I would classify as unstable joints and the ones most in need of stabilization through neurological retraining of the surrounding musculature. The joint has also been termed “compressed” in that as it is off its anatomical axis, its motion is curtailed abnormally. Thus, the feeling that it is not moving freely. This compressed joint can also be from high muscular tone around the structure.

A very telling statement by my friend, Rick Bibbs illustrates this well. “The ‘clunk’ is part of the range of motion and I’m not really relaxed with the motion until I get it.” I am sure this is a familiar sensation for a lot of individuals.

When a joint is manipulated, the joint capsule is distended and you hear a pop or clunk. The stretch on the capsule stimulates Type III joint mechanoreceptors which cause a neuroreflexive inhibition of surrounding muscles. This appears to be the most suitable explanation for the relaxation and ease that we feel. Another theory is that endogenous opiates are released as well. Thus, the good feeling after a high velocity thrust manipulation. Especially the multiple spinal levels that are engaged in most chiropractic procedures, and self manipulations. These can be quite addictive.

A very relevant debate is whether these manipulations should be repeated, or even performed at all. The usual warnings condemn your joints to arthritis, instability, or other such damage. Well, if they occur as a matter of course when you exercise and move, then the point is moot. It is, as they say, as it is. However, repeated high velocity (and especially high force) motions may not be the best thing to do to yourself. Though I am aware of no specific studies which prove damage occurring from repetitive manipulations of “normal” joints, significant anecdotal and empirical evidence exists. The most plausible, is that repetitive firing of the joint mechanoreceptors can lead to improper joint movement patterns, as the surrounding musculature is continually inhibited. Essentially, you are fiddling about with your proprioceptive mechanisms. Also, it has been shown the chronic inflammation decreases tissue stability. And it is well known that repetitive overstretching can bring about inflammation.

It should also be noted that these mechanoreceptors do not require the often accompanying sound to fire. The requirement is simply a force, preferably quick, at the endrange of the capsule’s extensibility. Osteopaths will be quick to point out that the sound is not the goal, rather freer movement is. Thus, the necessity of rechecking ROM after a procedure, instead of continuing the manipulation until you hear what you want!

Another common phenomenon is for crepitus to change over a period of time. It can become louder, more frequent, less frequent, be accompanied by pain, or suddenly become pain free. This is because angles of pull and axes of motion can change with increased/decreased muscle strength and flexibility, and with other changes in non-contractile soft tissue. It is not uncommon to observe crepitus appear and disappear during the course of an exercise regimen as bodily adaptations occur.

I would suggest that after you hear this pop or clunk, you should continue your active range of motion exercises. I say this because now that the joint is moving freely, this is the ideal time to perform joint strengthening exercises. Dynamic ROM such as Intu-Flow® or other therapeutic exercise will serve to prevent joint compression and enhance muscular strength (both neurological and structural), and flexibility. So, rather than the sounds being a goal, hindrance, or bane, it is just part and parcel of regaining your freedom of movement.