WHY DO MY KNEES CRACK?
“Why do my knees make a loud click?”
“Is my knee cracking bad for me?”
“Am I developing arthritis?”
“I am too young for this!”
Our joints clicking or cracking create a lot of negative emotions in people, and the above mentioned are some of the most common things that I hear in the clinic each week.
This audible clicking is a poorly understood concept, that has been found to cause significant amounts of worrying, anxiety, and fear avoidance behaviour in people (Robertson et al., 2017).
Firstly, let’s give this phenomenon an appropriate label…
“Crepitus” is the medical term used to describe any clicking, cracking, grating, popping or grinding sensations experienced in our joints.
So what exactly is going on here? And is knee crepitus something we should be worried about?
Well first of all, knee crepitus is absolutely normal! Studies have actually shown that a very high percentage of healthy people experience knee crepitus with no associated pain or pathology (McCoy et al., 1987).
The most recently published study looking at crepitus as a risk factor for arthritis did find a small correlation between crepitus and the development of knee OA (Lo et al., 2017), however the results of this trial were quite misleading. It must be noted that all subjects were only recruited for this study due to the fact that they had pre-existing risk factors for osteoarthritis (most notably age and an increased BMI). Also, the subjects with crepitus who went on to develop OA also had early x-ray findings of arthritic changes. Lastly, there was a significant amount of subjects with knee crepitus who never developed any symptoms or issues.
There has been no research to date that has showed any significant or definitive correlation between knee cracking and pathology, and the most current studies to date still do not provide us with any convincing evidence that crepitus can cause or lead to arthritis.
So if knee crepitus is normal, then why do they make an audible sound? What exactly is going on inside our joints?
Well there are a few possible explanations for what we are hearing, depending on the nature and location of the noise. It may be due to:
*Tendons snapping over bony protuberances (extra-articular crepitus, outside of the joint itself).
*Joint displacement causing a vacuum, leading to a collapse of gas bubbles in the synovial fluids (popping sound from deep inside a joint, similar to cracking your knuckles).
*Clunks or vibrations occurring between the patella and the femur, which are part of normal joint movement (this actually decreases in osteoarthritic knees due to hypomobility and loss of lubrication).
*Fine grating, as normal joint fluid flows through the rough retropatellar surface.
So we know that non-painful knee crepitus is normal, and there are several explanations as to why we hear these noises. But what if you are experiencing pain along with the crepitus?
Well we know that pain is our body’s protective response, and it encourages us to seek help or change our behaviour. So if you are experiencing knee pain, then a professional clinical assessment is always recommended, regardless if crepitus is prevalent or not.
Nevertheless, we can be confident that knee crepitus is completely normal, and NOT a sign of any serious pathology.
B. Health Sciences (Physio), APAM