thank you for your answer.your explanation was good.I think.you have chondromalacia of patella.you must avoid of any condition that made your knee full flexion.the physiotherapy is very benefit( such as ultrasound.heat.tens.taping.)hydrotherapy and exercise therapy( isometric exercise for quadriceps muscle. specially vastus medialis muscle and cocontraction of hamstring and quadriceps muscle)your knee pain can be disappear fully.you must go to physiotherapy clinic.excused me .if you have questions ,send me pm.i will be glad to help you.good luck