A new randomized-control trial study has just been published in the Journal of Orthopaedic and Sports Physical Therapy concerning exercise intervention of females with patellofemoral pain (front knee pain).
This study had two groups: the first being prescribed an exercise intervention concentrating on hip abduction and hip external rotation strengthening, the other group being the no-exercise control.
The exercise program consisted of two elastic band strengthening exercises of the hip done 3x/week. After 8 weeks the exercise group showed a significant decrease in pain as well as function (based on self administered survey), and the control (non-exercise) group had no change in either outcomes.
This shows that although you may be dealing with pain in one area (the knee), the source of the problem may be coming from another location along the kinetic chain (in this case, the hip)!
Khayambashi, K. et al. (2012). The Effects of Isolated Hip Abductor and External Rotator Muscle Strengthening on Pain, Health Status, and Hip Strength in Females With Patellofemoral Pain: A Randomized Control Trial. The Journal of Orthopaedic and Sports Physical Therapy, 42(1), 22-29.