Blood clots form because of pooling of the blood in the large veins in the legs. This occurs when patients move their legs less, such as either during surgery or when spending a time in bed recovering after surgery. Stress, such as from surgery or injury, causes the blood to clot in these pools to clot more easily. Combine these changes with thickening of the blood that can occur after surgery due to mild dehydration, and the result is an overall increased risk of blood clots forming in the legs. Your doctors will use early ambulation, automatic compression stockings, and blood thinners to prevent these clots from forming.