I'm a TBI patient, I used to smoke but now, I've quit for a long time, my knees won't bend, does stretching help, please fill me in ASAP.
Try sitting in a chair feet on plastic bag and slide feet backwards as far as possible each day push a little further might help
Doctors first and scans and X-rays etc would be my advice to make sure nothing underlying - you might get some physio from them.
Failing that stretching is a good idea not only for the knees but with general mobility and working the body - Google has a wealth of good ( and not so good) videos - I typed in ' can't bend knees'. And found some usual, gentle and sensible exercises and advice - might be worth a look but go at your pace and push yourself when you are ready
Yes stretching does help do all your exercises even if it hurts a lot .