Extremely loud And painfull pop sound.

I bent, overflexed my leg sideways playing volleyball. It then made a pop while i was starightening out the leg. Noé i have to be carefull of how i sit, if i bebend my leg it Wiill lock and nake a pop sound and it hurts after the pop. If i manadge to to go a day withouhght locking it it wont hurt unless i try to get downln in a squating position. I have gone to gone to a specialist 2 times Now and have taken an mri. The doctor thinks theres a piece of cartalige hangin around but the mri didntbshow anything. The meniscus where fine and there was a minor contusión somewhere... But what i Sony get is theres no problem in the mri and m knee keeps dislocating or popping!! Sorry for the spelling im using an iPhone.