I am a Physical Therapist Mostly dealing with Total Knee replacement
Swelling over foot and ankle is the most common problem faced by patients post knee replacement. As you have mentioned that you also have foot drop
, so the reason seems to be for swelling is your limited right foot up and down movement(i.e dorsi flexion and plantar flexion) because of which your calf muscle action is limited. unless and until your calf muscle is not working properly, fluid movements from foot and ankle will be limited and that is the main reason for your right foot swelling.
So trying to work on your foot drop issue and i believe your swelling will be gone.
I hope i have answered your query.