Why knee is warm after total knee replasment.

Incresed blood flow. After an injury or surgery, there is increased blood flow to the injured area. Due to small blood vessel damage, there is also some swelling in the area. This leads to increased warmth in the knee. This can last for several months as the soft tissues continue to heal around the knee.
Very common. Warmth to touch is a very non-specific finding, often representing anything from healing, swelling, inflammation, or infection. After knee replacement, increased warmth to touch is common for 8-10 weeks due to increased blood flow during the healing process.