I Have Arthritis In The Left Knee. Over The Years

I have arthritis in the left knee. Over the years I've had about three orthoscopic surgeries in the left knee. Recently I've been having that can best be described as a collapsing feeling of the left leg from the knee down. The source appears to originate from behind the knee near the outside and then radiates down and inward toward the chin area. If I relax or put an ice pack on it subsides until the next time. I thought at first it might the pressure of my white cotton socks so started wearing the ankle socks. It appeared to work for awhile, but the symptoms returned. It can also occur after a few minutes of walking or as soon as getting up to start walking. Aleve and the like appear to have no effect. What might be the cause?