Thanks for your question on HCM.
I can understand your situation and problem.
By your history and description, in my opinion you are having post operative joint abscess
which is now coming out under skin.
Following are the points which favours this diagnosis.
1. History of arthroscopic surgery
and not improving after surgery
2. Enlarging swelling which is painful on touch.
3. Overlying skin point is whitish (pus point).
So better to consult orthopedic doctor and get done
1. Clinical examination of knee joint
examination of local part
of that knee joint.
You may need revision surgery.
So better to consult orthopedic doctor and discuss all these.