This study published in the Annals of Internal Medicine found an increase in knee pain of 65% over the past 20 years. This correlates with an increase in knee replacement surgery. Interestingly, most of the knee pain did not show changes on x-ray leading me to question whether this is degenerative knee pain or nerve pain coming from the low back causing referred pain to the knee. Most knee pain cases I have seen have a component of leg muscle weakness coming from nerve compression in the low back. Fixing the low back typically fixes the knee. I have developed a sensitive and specific physical test to tell whether your knee pain is all or in part coming from your back. Injury, chronic overuse and autoimmunity are other possible causes. Either way, there are solutions without the use of drugs or surgery.