Possibilities that may need to be considered include patellar dislocation, chondromalacia, fractures, injuries to the internal ligaments/ menisci, infections/ inflammations, arthritis, bursitis, tendonitis, cyst formation, iliotibial band syndrome, bone
growths/ tumours, nerve injuries/ impingement etc. I would suggest considering an evaluation by an orthopedician for an accurate diagnosis and appropriate management.
Hope this helps.
Take care!