People who undergo total knee or hip replacement may not need prolonged or aggressive therapy to prevent blood clots, according to two preliminary studies presented recently at the 2012 meeting of the American Academy of Orthopaedic Surgeons. The two studies add to the growing body of literature of ways to prevent blood clots after joint replacement surgery, but neither one settles the issue. 

After total joint replacement, patients typically receive anti-clotting medications such as warfarin, or Coumadin, to help prevent deep vein thrombosis, or DVT –  blood clots in the calf or thigh. Orthopaedic surgery increases the risk of clots, which can block a vein or detach and travel to the lungs. A blockage in one of the lung’s arteries – a condition called pulmonary embolism, or PE – can be life-threatening. The American Academy of Orthopaedic Surgeons, or AAOS, and the American College of Chest Physicians, or ACCP, each has guidelines to prevent clotting in joint replacement patients.

Although anticoagulants reduce the likelihood of DVT, they don't entirely prevent it. Additionally, the drugs carry risks, including postoperative bleeding, joint infection and hematoma, says Javad Parvizi, MD, professor of orthopaedic surgery at the Rothman Institute, Thomas Jefferson University Hospital in Philadelphia.

"Some of the complications [of anticoagulants] can be more dire than DVT," Dr. Parvizi says. "The more aggressive the agents and the longer they are used, the higher the risk of side effects."

He emphasizes that there is no consensus on how long anticoagulation therapy should be continued to reduce the risk of pulmonary embolism and DVT. To help determine a safe and effective duration of treatment, Dr. Parvizi and colleagues retrospectively reviewed the medical records of 26,415 patients who underwent total hip or knee replacement at Thomas Jefferson University Hospital between 2000 and 2010.

All patients received the anti-clotting drug heparin during surgery and warfarin for six weeks after surgery. A special clinic monitored their warfarin levels and adjusted doses as needed.

In all, 283 patients developed pulmonary embolism – 1.66 percent of those undergoing knee procedures and 0.48 percent of hip surgery patients. Women were more likely to develop PE than men (1.21 percent and 0.84 percent, respectively) and the incidence of PE increased with age, with the highest rates occurring in patients ages 71 to 80.

Eighty-one percent of patients who developed PE did so in the first three days after surgery, and 93 percent of PEs had occurred by the end of the second postoperative week. There was little difference in the timing of PE between patients undergoing hip and knee procedures or between men and women.

Dr. Parvizi says the study – the first of its kind – demonstrates that most PE seems to occur in the first two weeks after joint replacement surgery. Other, smaller studies have shown the risk to extend for four weeks or longer.

"The older literature talks about patients at high risk of PE [for a prolonged time after surgery], but orthopaedic surgery is performed very differently today," Dr. Parvizi points out. "We now use spinal anesthesia, which is known to reduce the risk of thromboembolism; we have patients ambulating right after surgery, and they are out of the hospital in one or two days. We have really come a long way from the early days, when these operations were much more physiologically taxing than they are now."

Based on his findings, Dr. Parvizi believes it is safe to reduce the length of anticoagulation doses in all patients except those with venous disease or clotting disorders.