Hi and thanks for this query.
I a sorry to hear about all that you have been experiencing.
Crossing legs for a long time reduces the amount of blood flow to the lower limbs
. This results in low oxygen
and nutrients supply. This will inevitably lead to muscle cramp that will cause you to feel pains. It usually takes a while after putting the legs in a straight position for the symptoms to go away. So avoid crossing your legs for long or better still cross them at the ankles and not the knees for better outcome.
From the history of knee trauma and your leg giving out on you, it may be that you had a tear of one of the stabilising structures at the knees. You should meet and get the leg examined and also may need a test to evaluate all the essential structures at the knee to tell what the problem is.
Hope you find this helpful.
I wish you good health.