Updated May 20, 2015.

Blood clots in the large veins (deep venous thrombosis, or DVT) of the leg and pelvis are common after orthopedic surgery, especially joint replacement surgery. The risk of developing a blood clot depends on several factors including the type of surgery, other medical problems, medications you may be taking, smoking history, as well as other factors.

Medication to Lower the Risk of Blood Clots

If the risk of developing a blood clot is thought to be high, your doctor may start you on blood thinning medication after your surgery.

This is standard following joint replacement surgery such as total knee replacement and total hip replacement surgery. Blood thinning medication may also be used following other procedures, especially large surgeries of the lower extremities.
Other modalities used to decrease the risk of blood clot formation include compression stockings to keep the blood in the legs circulating and pumps around the legs to stimulate blood flow through the veins. Early mobilization after surgery is also very important and will help prevent blood clot formation.

Blood Clots In The Lung

The concern of a DVT is that if a blood clot develops, it is possible that it can travel to the lungs (called a pulmonary embolism), which can potentially be fatal. If your doctor finds evidence of blood clot formation, you will likely be given a higher dose of blood thinning medication for a longer period of time.
Why aren't all patients given blood thinning medication?
The problem is that there are risks of blood thinning medication, such as a stroke, gastrointestinal bleeding, and other problems.

While the risk of developing a stroke from blood thinning medication is small, only patients who are at high risk for developing a blood clot should be started on blood thinning medication.