Special stockings commonly given to stroke patients to prevent blood clots don't work, a new study reported Wednesday. Doctors often prescribe the tight, thigh-high stockings to patients who have suffered a stroke, seeking to prevent blood clots in patients' legs — which could prove fatal if they break off and reach the heart or lungs. About two-thirds of stroke patients can't walk when admitted to hospital, and up to 20 percent of those patients develop a blood clot in their legs. The stockings squash the legs and force the blood to circulate better, and can be used in place of, or alongside, anti-clotting drugs like heparin. But in a study of more than 2,500 stroke patients in Australia, Britain and Italy, doctors found the stockings did nothing to reduce the chances of a clot. Not only that, but they caused problems like skin ulcers and blisters. The results were simultaneously published in the Lancet medical journal and presented at the European Stroke Conference in Stockholm on Wednesday.