Pain in left knee. Burning sensation. Intermittent. Arthritis ruled out by X-ray. Pain makes sleep almost impossible. Can radiate up into thigh and down calf, sometimes reaching foot. Had for approximately 20 years. Becoming more present as time passes. Pain is on the left side both front and back. Pain does not affect patella. I am 60 years old patientof age. Female. GP has no idea. He thought it was arthritis until X-ray ruled that out. When walking down stairs, I have to angle my foot toward the right as walking straight can trigger pain or aggravate it if already present. When standing, cannot hold leg very straight or same can happen. I have to keep leg somewhat relaxed. Stairs can aggravate or cause pain as can ramps. I am getting a bit desperate. Latest episode is of 5 days duration, not constant but easily triggered. Worst when I lie down to sleep. Cannot lie on stomach. In the past, using a pillow for support with a heating pad has helped but this time that is not helping. Can anyone offer any help? Grace Turner.