No, it is not normal, and one of the most common causes is Osteoarthritis, which is a degenerative arthritis that commonly affects the large weight-bearing joints as the knees. It is mostly related to aging, when the water content of cartilage increases and the protein makeup of cartilage degenerate. The cartilage begins to lose proteins causing flaking and forming crevasses until that in advanced cases there is a total loss of cartilage cushion between the bones of the joints, causing friction, leading to pain and limitation of joint mobility.
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