It is important in this phase to maintain circulation. The lower leg is very dependent upon a 'muscle pump' in the calf. As one walks the muscle contraction and relaxation helps to keep the venous blood going back to the heart. If one is confined to bed or the sofa and the leg is immobilised this muscle pump is not working.
A useful exercise to stimulate the muscle pump is 'foot pumps.
Elevating the leg is also useful in keeping the venous blood flowing.
After surgery the surgeon may order tight 'TED' stockings which help to prevent the blood flow slowing down and forming clots in the veins (deep vein thrombosis). Anti-coagulant (anti-clotting) medication is also normal during and immediately after knee surgery.