My mom has knee pain.Whats she suffering from?

The other answerer is not correct. Studies have shown that arthritis (meaning osteoarthritis) does not cause pain. It's too bad that so many doctors and surgeons erroneously believe that it does, just because osteoarthritis shows up on the X-rays--but they make a lot of money performing surgeries, they don't want to hear the truth. The truth is that osteoarthritis is a normal part of the aging process, just like getting wrinkles. Chances are that your mother has something called TMS--tension myositis syndrome. Watch the youtube.com video "Dr. John Sarno 20/20." Although it talks mostly about low back pain, it applies to knee pain, too. Listen to Rosie O'Donnell's employee, how she had pain all over her body but got better in 2 weeks after learning about TMS. I believe it will help your mother, too.

Most common reason for knee pain in older people is arthritis.

Only a doctor could diagnose this for sure.