Hi there!
Well, without an evaluation it would be difficult to determine the cause of the knee pain. Possibilities that may need to be considered include patellar dislocation, chondromalacia patellae, infections/ inflammations, arthritis, bursitis, tendonitis, cyst formation, iliotibial band syndrome, osgood schlatter disease, bone growths/ tumours, nerve impingement/ compression, fractures, injuries to the internal knee ligaments/ menisci etc; just to name a few.