Surgery and immobilization can precipitate deep venous thrombosis, and the clot can break loose and lodge in the lung. There is excess risk for a month or more afterwards. The leg is the most frequent source of the clot. A Forcier, NA Patwardhan. Consensus Group .
Recent studies say nothing about the effects of smoking.
Smoking does not appear on any of their list of risk factors. In fact, between 1974 and 1980, it was discovered, to everybody's surprise, that non-smokers were at considerably greater risk for deep venous thrombosis. It seems they would rather say nothing at all, than to admit that smoking is not a risk factor, let alone that non-smoking is one. Increased incidence of deep vein thrombosis after myocardial infarction in nonsmokers . Preoperative prediction of postoperative deep vein thrombosis .