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Low-Molecular-Weight Heparin Given for Several Weeks after Hip Surgery Prevents Deep Venous Thrombosis
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What is the problem and what is known about it so far?
After surgery, some people get blood clots in the deep veins of their legs, a condition known as deep venous thrombosis. Pieces of these clots, called emboli, can break off and travel through the bloodstream, blocking arteries in the lungs. The blood clots and emboli can cause serious symptoms and even death. Surgery to repair or replace hip joints (arthroplasty) has a particularly high risk for causing blood clots in the legs. These increased risks last several weeks after surgery. Patients who have hip surgery routinely receive medications known as blood thinners (for example, heparin or warfarin) to prevent clots from forming in their legs. Several years ago, researchers made a new form of one of these blood-thinning medications—low-molecular-weight heparin (LMWH). This drug is given as a shot and, unlike other blood thinners (such as warfarin or intravenous heparin), does not require frequent monitoring with blood tests. However, the exact benefits and harms of giving LMWH for several weeks after hip surgery have been unclear.
Why did the researchers do this particular study?
To find out whether LMWH given for several weeks after hip arthroplasty prevents blood clots from forming in the legs.
Who was studied?
1953 patients who had participated in previously published studies of LMWH. Most were older adults who had been hospitalized for 1 to 2 weeks after elective hip surgery. All had received blood-thinning medications while in the hospital.
How was the study done?
The researchers analyzed information from six studies that randomly assigned patients who had undergone hip surgery to receive LMWH or placebo (“dummy” shots, which contain no active ingredient) once daily. Patients were followed after hospital discharge for 3 to 4 weeks. They had special x-ray dye tests (venography) to look for deep-vein clots in their legs. The researchers compared the number of deep-vein clots that developed in patients given heparin shots with those that developed in patients given placebo shots.
What did the researchers find?
Clots in the deep veins of the leg were found in 8% of patients given LMWH compared with 23% of those given placebo shots. One percent of patients given LMWH shots had symptoms related to their clots compared with 4% of those given placebo shots. Two patients given placebo shots died of lung emboli. Serious bleeding after surgery occurred in one patient who had been assigned to placebo shots and in no patients who got LMWH shots.
What were the limitations of the study?
Some people, such as those who are overweight, are older than 85 years of age, or have a history of blood clots, may have a very high risk for clotting after hip surgery, whereas others who are younger and more active may have a lower risk. Whether LMWH benefits all types of patients, including those at low risk, was not studied.
What are the implications of the study?
Patients who have surgery to repair or replace their hip joints should receive blood-thinning medications, such as LMWH, for up to 4 to 6 weeks after surgery.
Article and Author Information
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The summary below is from the full report titled “Extended Out-of-Hospital Low-Molecular-Weight Heparin Prophylaxis against Deep Venous Thrombosis in Patients after Elective Hip Arthroplasty: A Systematic Review.” It is in the 20 November 2001 issue of Annals of Internal Medicine (volume 135, pages 858–869). The authors are RD Hull, GF Pineo, PD Stein, AF Mah, SM MacIsaac, OE Dahl, M Butcher, RF Brant, WA Ghali, D Bergqvist, and GE Raskob.
- Copyright ©2004 by the American College of Physicians
