Hi guys. I'm 40 and had Osgood-Schlatters disease from the age of eight. I put up with the pain until two years ago, when I had a simple op under gen asthetic. Quite a lot of sportsmen develop this condition, and some women. Had no probs since then. It's great. Op was in Perth-Western Australia, and involves splitting the tendon below the knee and removing inflammatory material.
"The patella tendon inserts at the tibial tuberosity and through overuse can tug away at the bone causing inflammation. It is seen more often in children involved with running and jumping activities which put a much greater strain on the patella tendon. With repeated trauma New bone grows back during the healing which causes a bony lump which is often felt at the tibial tuberosity. It mainly affects boys aged 10 to 16 years old and will clear up when they stop growing and the tendons become stronger, however, it can rarely persist into adulthood."
http://www.sportsinjuryclinic.net/cybertherapist/front/knee/osgood.htm will tell you more.
Using thin (10mm) strapping tape between the patella and the swelling during sport helps.
My 12 Y O daughter also has the same. She will have an Op a soon as she stops growing.