Pain due to 'adhesions' following knee surgery?

I had the outside (lateral) cartilage of my left knee removed after a sports injury in 1987; 24 years ago. Ever since I have had pain in the knee and it has restricted my sporting activities. I recently had the knee examined by a consultant orthopaedic surgeon who told me there was no evidence of osteo-arthritis in the knee and that the pain might be due to the formation of 'adhesions' following the original surgery undertaken before the days of keyhole surgery techniques. Other symptoms I have are a continual feeling that I need to flex the knee joint at regular intervals throughout the day. The site of the incision has always been slightly numb and the knee is moderately painful some days and only slightly painful on other days. The pain is never severe and there is never swelling or fluid on the knee. Can anyone explain more to me about 'Adhesions' please?