From your history it seems that knee replacement
But if delay of replacement is unavoidable then do following things,
1, Totally stop using stair case.
2, Wear knee cap to support knee muscles, remove at night.
3, Do patellar exercise daily 10 minutes in the morning and evening.
4, Do not on sit in squatting position or cross legs or more bend from the joint.
5, Take some Calcium, vitamin A
and D. supplements.
Ok and take care.