snap sound during PT , from almost full recovery - advice needed

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all, I want to get your input on something - it has been 5 months from my surgery and more than 3 months since I stopped lengthening, I had been doing well walking fine, walking up down stairs, walking very fast. Except running I tried everything, and was close to normal (though when I seat on the floor with folded legs, the muscles in knee cap give some strain, so am still continuing to stretch). Yesterday I was wondering if I need professional PT any more because I am doing same exercises at home though they are at times giving me different and tough exercises because per them my bum muscles are not strong enough yet (which might be true but I think doing daily normal activities and walking and taking vitamin and calcium and good food will anyway take me to near 100% recovery without weird and difficult and potentially dangerous exercises - because remember it is only 3 months post lengthening) - so I was thinking last night that I am just losing more money on PT and would recover fully anyway from here on my own and should stop professional PT. Anyway, I should have acted on my thought last night because something very bad and scary happened today (though I don't know how bad or scary it is) - they made me stand on one leg on a narrow brick kind of thing and asked me to bend my knees and then straighten the knees and repeat it 5-6 times (which I think is asking for trouble even with stryde's weight bearing ability, my weight is like 160lb),  repeated twice , in the second attempt suddenly there was a snapping/cracking sound and sudden pain above my left knee cap (lower area of left femur) , and they (PTs) and I were worried what happened, the pain was gone soon and they did some tests and said it is nothing it must be some 'scar tissue' (I have no idea what that is) - I asked them can it be related to bone or rod and do I need x ray - per them I don't need x ray because if it were bone crack or anything like that I would be in great pain. but then walking my way back home I felt some pain (very low like .75, even less than 1) and am getting the pain when I am walking now. What is your opinion on this topic? in the past also I think I had to get bedridden for 10 days because of heavy and too aggressive exercises resulted in quad pull and I had to tell them that I will NOT do any exercise for 2 weeks, then only I was able to recover (by listening to my body and my brain rather than the PTs). What should I do about this new situation now? thanks.

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ok, so you think it might be serious? thanks I just wanted additional opinions like this because per them (PTs) and their tests it was nothing so I did not bother to ask the doctor. It is 11 PM now, first thing tomorrow I will ask the doctor and maybe also get an x-ray done.

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Thanks all, I have asked the doc to send an x-ray request to my nearby imaging center to be sure that is is nothing big , anyway I needed the X-ray because last one I had was like 2 months back !!
I did not receive any PM