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.
 

"Everyone is concerned about preventing blood clots," he says, "but the risks of blood thinners far outweigh the benefits. A blood clot is not as much of an issue as paralysis that results from bleeding into the spinal cord or a severe stroke from bleeding into the brain. Patients think that because they're taking drugs, they won't have a problem, but that's not always the case."

Dr. Parvizi's study has been accepted for publication in The Journal of Arthroplasty.

Aspirin also can lower the risk of DVT and PE

In another study, Japanese researchers investigated the incidence of DVT and PE in total joint replacement patients treated with aspirin and mechanical prophylaxis, such as compression stockings and foot pumps.

Principal investigator Koh Shimizu, MD, an orthopaedic surgeon at Chiba Rosai Hospital in Japan undertook the study after a patient experienced severe cerebral bleeding from anticoagulation therapy. "This sad experience made me realize that the prevention of DVT and PE is absolutely necessary, but an excessive amount of anticoagulation is worse than doing nothing," he says.

Dr. Shimizu and his colleagues followed 1,500 patients prospectively for DVT for 10 days after total joint replacement.. All patients wore elastic stockings and were started on a foot pump, which provides intermittant compression, immediately after surgery. Two days later, each began a month-long regimen of 162 mg of daily aspirin, and continued taking a half dose for another three months. Venography, a test for DVT, was performed preoperatively and 10 days after surgery.

The overall incidence of DVT was 19.2 percent, with most clots occurring in knee replacement patients. One hip replacement patient developed mild PE, whereas no knee surgery patients did. There were no complications from the aspirin.

Dr. Shimizu says the incidence of DVT was far lower than in patients receiving no preventive treatment but admits it was higher than in people receiving anti-clotting therapy. "Strong anticoagulants containing LMWH [low-molecular-weight heparin] and warfarin increase hemorrhage and infection, although they can effectively decrease DVT and PE. Mild anticoagulants containing aspirin and [standard] heparin are safe, although the occurrence of DVT may be more frequent," he explains.

Although convinced of the safety and efficacy of aspirin therapy, Dr. Shimizu believes high-risk patients need stronger medications.

"In this study, gender, age, body mass index, preoperative venous abnormalities and preoperative range of motion were thought to be risk factors for DVT. Therefore, for patients with many risk factors – for example, older women who are overweight and have limited range of motion – we recommend the use of anticoagulant therapy. For these patients, mechanical prophylaxis should [also] be used more aggressively, since this has no side effects."

Benjamin C. Bengs, MD, an orthopaedic surgeon at UCLA Medical Center, points out that neither study is conclusive and that there are a number of conflicting studies on DVT prevention.

"These are just two of many articles on this subject, all of which have slightly different takes," Dr. Bengs says. [For instance], some studies say that aspirin is the equivalent, or almost the equivalent, of Coumadin [in its ability to prevent blood clots], but others show the contrary. There is a huge body of literature and a number of differing opinions, and I don't think that these studies alone allow [physicians] to change the standard of care."

However, he says, the studies help the ongoing effort to safely prevent blood clots after joint surgery.

"I think surgeons can take this new data plus guidance from the representative academies – the American College of Chest Surgeons and the AAOS – add their own clinical judgment, and proceed from there," Dr. Bengs says.