Have you had physio? I have had knee pain since child hood but no apparent cause. Recently however I have had surgery for a large miniscus tear.My physio says that my knee muscle which controls the placement of the knee cap (On the inner side of the leg just over the knee) is weak in both legs and this could have contributed to my miniscus being vunerable. My surgeon says that long term outside of physio that swimming and stationary cycling are the best ways to strengthen these muscles i think they refered to them as vmo's, and prevent future injury. My three young children all also complain of knee pain and occasional problems such as the knee buckling. For them I am trying to make sure they have a good diet ( protein fish oils calcium etc) and plenty of exercise to keep their muscles strong (ballet and yoga are good)> i have been taking a joint support supplement, silica and fish oils keeping fingers crossed that op will be a success, i have 2 weeks to go of 12 weeks in a locked brace (Boring!) Best of luck and take good care of yourself.