The truth: The reason our knuckles crack when we stretch or bend them is because the synovial fluid (inside them) is bursting. This is the fluid that lubricates our joints and it receives all the pressure that comes from cracking. Many studies have shown that this habit doesn’t cause arthritis, but you might need to quit it for a different reason. What we know is that chronic knuckle cracking can cause your hand to have a weaker grip.