What would cause ankle and foot swelling after surgery to the knee?

Swelling: Typically knee surgery can affect the venous outflow from the lower limb and cause swelling below the surgical site. Also if compression dressing or wraps are applied to the knee this will cause an increase in the fluid retention.

Post-operative swell: Swelling travels with gravity. After most surgeries to lower extremities, the surgeon will instruct patients to keep their legs raised. This is so the swelling (fluid) doesn't build up following the flow of gravity to the foot and ankle. Although there may not be any procedures done to those areas, fluid can travel along a path of gravity and teh foot and ankle are at the bottom.