Lt ankle tendon surgery 2 weeks ago now pitting edema. What can cause this? Slight redness and warmth on ankle bone.

Surgery. Infection is always a possibility as you do not state the status of the incision. For any concerns see your surgeon .
Multi factorial. Any fevers? Nausea? Vomiting? Shortness of breath? Is the edema on both sides or just one? While an infection is unlikely this far out, it needs to be rules out. More likely, it sounds that is surgery related. What surgery was performed? I'd need a better history but clots and infection need to be ruled out first, the rest can be dealt with and worked up.