I know your son is 6, but when I was 2 years old my parents said I woke up one morning and all the sudden I couldn't walk for pain in my left knee. Of course I don't remember too much of it because I was only 2, but I have heard all of the stories from family. My parents took me to Kansas City Children's Research Hospital and since my knee was swollen they decided...after lots of tests, that I had juvenile arthritis. So they pumped me full of lots of lots of painkillers and I went back every so often for blood work and checkups. I totally, even though I was only 2, remember being poked by the needle each time. The doctors were telling my parents that I may be in a wheel chair for the rest of my life. That was a devistating thought to them of course. One day while at work my mom's friend said "you should take her to a chiropractor". Well, EVERYONE in my family was totally against the idea, but I wasn't getting any better and my mom felt she had no choice. As I was a very active child and it killed her to see me sitting on the sideline of all the fun activities my cousins were doing. So, against everyone's wishes including my father's she secretively took me to her friend Chiropractor. He took one look at me and said "I need an xray". That is key....never let a Chiropractor touch you unless they take xrays. That is a good way to tell a quack from the real deal. He knew that even though my knee was swollen, it didn't mean it was my knee that was injured. Sure enough it wasn't, it was my hip. He told my mom he would not touch me until she took me off all the medication the doctors had put me on because the meds were really hurting my kidneys at such strong doses. When a child's hip pop's out of place it then causes undo pressure on knees, ankles, back. It causes swelling and pain in other areas besides the hip. I don't know if that is what is wrong with your son, but I just don't want anyone to go through what my parents and I went through for months before finding out what the real, simple to solve problem was. After a few, unpainful visits to Dr. Morgan, my chiropractor, I was running and playing like a normal kid again. I was the Chiropractors youngest patient and to this day he still remembers me.