4 out of 10 have ‘clicking knees’: how is that and when do you have to go to the doctor?

It is a quiet morning. You are fully enjoying a wonderful autumn walk until you suddenly hear a soft grinding sound. However, it does not come from the gravel under your feet, but from your knee. Why does it make such a sound? How many people suffer from clicking knees? Is this an omen of something worse such as rheumatism? And can you do something about it? HLN science journalist Martijn Peters delves into a study that it all sorted out.

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