One question we get all the time at Back in Action is “why do my joints pop and crack.” Well, it’s a question that has bugged us humans for a very very long time. In fact, there is evidence that we’ve been trying to figure it out since 3,000 BC when the surgeon of the Old Kingdom in Egypt developed a working knowledge of the jaw joint.3 In more modern times, medical texts started addressing joint noises with C Heuter looking into it in 1885 and then Blodgett starting to listen to joints with a stethoscope in 1902.
We’ve come a long way since 3,000 BC and have a better understanding of why joints make noise, though there is not one single answer. Shoulders, elbows, wrists, fingers, backs, hips, knees, and ankles can all pop or crack for different reasons.
Here are some specific answers to what the noises are in certain joints:
Knuckles: A study in 2015 took a real time MRI of cracking finger joints and actually found that “joint cracking is associated with cavity inception rather than collapse of a pre-existing bubble.2” I thought this was interesting! The noise is actually a formation of a bubble in fluid, not the popping of a bubble. It’s a phenomenon called tribonucleation and it happens quite a bit in both nature and industry.
Spine: It’s thought that the popping in your spine when you crack your neck or back is similar to what happens when you crack your knuckles, though this has been harder to confirm and could be due to something different.
Hip: The hip can pop for a lot of reasons. Two of the most common sources of popping are the outside of the hip or deep in the front of the hip. On the side of the hip, the popping is likely the big muscles and tendons rubbing over a bony prominence and bursa on the outside of the hip known as the greater trochanter/greater trochanteric bursa (a bursa is best thought of as a natural cushion between tendons/ligaments and bones). Deep in the front of the hip, popping is often referred to as “dancers hip.” Again, this popping is most often thought to be related to the hip flexor muscles rolling over a bony prominence and/or bursa.
Knees: the fine noise coming from knees is commonly coming from behind the knee cap. It is generally thought to be fluid moving over the surfaces behind the knee cap.6 Louder more abrupt pops from the knees are more likely tendons or ligaments quickly rolling over a boney surface or a bursa (there’s that word again).
William Kormos, M.D, Editor in Chief at Harvard Men’s Health Watch had this to say about cracking and popping joints. “The good news is that the usual painless joint cracking or popping does not represent an early form of arthritis, nor does it cause joint damage (despite what our mothers told us about cracking our knuckles). The cracking sound appears to come from tendons or muscles moving over the joint or from…nitrogen bubbles normally found in the joint space… Tight muscles and tendons may contribute, which is why cracking often occurs when you first rise from bed or a chair.”1 This may happen increasingly as we age because, as a normal process of aging, our muscles lose flexibility and tendons and ligaments because stiffer. However, Dr. Kornos goes on to say that “sometimes the noise is related to worn cartilage in the joints and bones rubbing together, which can cause pain.”
So, to sum it all up, the vast majority of popping joints aren’t a big deal and noisy joints aren’t necessarily a sign that your joint is being damaged. But if your joints are painful, or if you just want a professional opinion because you’re feeling a little unsure and want some peace of mind, our physical therapists will be happy to take a look!
- Kawchuk GN1, Fryer J2, Jaremko JL3, Zeng H4, Rowe L5, Thompson R6. Real-time visualization of joint cavitation. PLoS One. 2015 Apr 15;10(4):e0119470. doi: 10.1371/journal.pone.0119470. eCollection 2015.
- Freese, A., D.D.S.The Differential Diagnosis of Temporomandibular Joint Pain. AMA Arch Otolaryngol. 1960;71(5):789-792. doi:10.1001/archotol.1960.03770050049007
- Claire J Robertson. Editorial Joint crepitus — are we failing our patients? Physiotherapy Research International. First published: 28 October 2010. https://doi.org/10.1002/pri.492