My mother’s knees are swollen

Dear doctor; My mother has both her knees swollen real big and they give her difficulty in walking. She used to walk a lot to work. She has been taking medication, mainly painkillers, but it is the swelling and inconvenience that disturbs. Could this be arthritis yet she used to walk a lot to work until recently? Do arthritis affect people who walk a lot too? She is 57 now.
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Times Reporter