INATE - INvestigators Against ThromboEmbolism
Preventing thrombosis after orthopedic surgery

This article defines orthopedic surgery and discusses the prevention of thrombosis after surgery.



Introduction
What is orthopedic surgery?
What is thrombosis?
How is thrombosis prevented?
When will I receive medication?
References

Introduction
Major operations can increase the risk of venous thrombosis, especially if the operation involves the lower half of the body. Orthopedic surgery of the hip or knee, for example, can sometimes damage the wall of a vein and this can cause thrombosis. Being unable to move for a long time (for example, because you need bedrest) can also cause thrombosis, so if you have had or may need orthopedic surgery there are some important things that you should know about thrombosis

What is orthopedic surgery?
Orthopedics is a type of medical specialty that focuses on how your bones, muscles and joints work together. You may need orthopedic surgery if your hip or knee is damaged or worn out. In hip or knee replacement surgery, the damaged joint is replaced by an artificial one. If you have fractured a bone in your hip in a fall or other accident, you may need hip-fracture surgery. These types of orthopedic surgery will help you to become active again (after a period of rest) but may increase your risk of developing venous thrombosis.

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What is thrombosis?
Thrombosis is the development of a blood clot in a vein. If a blot clot forms in a vein that is deep within the muscles of the leg, it is called deep-vein thrombosis, or DVT for short. This type of thrombosis is a common medical problem after surgery and it can cause pain and swelling in the leg. It is not life-threatening but, if a blood clot breaks into pieces and travels through the body to the lungs, it can block the flow of blood through the lungs. This is called pulmonary embolism or PE for short. It is important to prevent PE because it can be life-threatening if not treated quickly. There are several things that can be done to reduce your chances of having thrombosis after surgery.

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How is thrombosis prevented?
Certain medications called anticoagulants (sometimes also called 'blood thinners') can prevent blood clots from forming. There are several different types of anticoagulants:
  • low-molecular-weight heparin (LMWH) – LMWH is usually recommended if you have to undergo orthopedic surgery. LMWH works quickly and you can even inject it at home under your skin once or twice a day. It is highly effective in preventing blood clots
  • blood-thinner pills (warfarin or coumarine derivatives) – blood-thinner pills have been used for many years to prevent thrombosis. They can take at least 3 days before they become effective, and you will need to be careful with your diet and to have your blood tested regularly
  • low-dose aspirin – aspirin is easy to use and works quickly but seems to be less effective in preventing blood clots, so it is usually not recommended for patients who have had orthopedic surgery
  • unfractionated heparin (UFH) – UFH is an older form of heparin. It is given by injection under the skin, usually twice a day. Although it will prevent blood clots in the leg following orthopedic surgery, it is not as effective as LMWH
There are other, newer types of anticoagulants, for example those known as 'pentasaccharides', that can also prevent thrombosis after orthopedic surgery. Your doctor will decide which medication is best for you, depending on the type of surgery you are having and other health factors.

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When will I receive medication?
If you have to undergo orthopedic surgery, you will usually receive medication to prevent venous thrombosis while you are in hospital. This anticoagulant medication begins just before or after surgery and continues while you are in hospital. This is because the risk of thrombosis is greatest during the first few weeks after surgery. In some cases, however, thrombosis can occur several weeks or even months after surgery. For this reason, your doctor may decide to continue your medication after you leave hospital.

How long you take anticoagulant medication also depends on other factors, including your general health. Your medication will help to stop blood clots from forming but will also sometimes disturb normal clotting that is needed to heal cuts, bruises and other wounds. Taking anticoagulants can sometimes increase your risk of bleeding problems. Your doctor will therefore look at both your risk of thrombosis and your risk of bleeding problems to decide how long you should take the medication.

Your doctor will also consider other factors that may affect your risk of thrombosis. These risk factors include your age, sex, weight, and whether or not you have had thrombosis before. If you are at high risk of thrombosis, your doctor may decide to continue your medication for longer.

The type of anticoagulant that you take may also help determine how long your treatment will last. Not every type of anticoagulant has been tested for long-term use. Doctors have studied LMWH, however, and have found that, in almost all patients, taking LMWH for about 3 to 4 weeks after surgery safely prevents thrombosis.

Lastly, the type of surgery you undergo can determine the type of anticoagulant medication you take and for how long:

  • total hip replacement – the increased risk of thrombosis after a total hip replacement lasts for 1 to 2 months. Usually, LMWH or blood-thinner pills are recommended to prevent thrombosis after a total hip replacement. If you are at high risk of thrombosis, it is usually recommended that you continue taking LMWH for at least 4 weeks after you leave hospital
  • total knee replacement – patients having a total knee replacement are also at high risk of venous thrombosis. Thrombosis is more likely to occur sooner after a total knee replacement. Usually, LMWH is recommended to prevent thrombosis, although blood-thinner pills can also be used. Because your stay in hospital can be quite short after total knee replacement, you may need to continue your medication after you have been discharged from hospital. The benefit of long-term medication after a total knee replacement is less clear
  • hip-fracture surgery – little is known about when thrombosis is likely to occur after hip-fracture surgery. Usually, LMWH or blood-thinner pills are recommended to prevent thrombosis after hip-fracture surgery. If you are at high risk of thrombosis, it is recommended that you continue taking LMWH for at least 4 weeks after you leave hospital
Despite these recommendations, it is important to remember that your doctor will decide what type of anticoagulant medication you should have, and how long you should take it, based on your individual case.

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References
Bergqvist D et al. Low-molecular-weight heparin (enoxaparin) as prophylaxis against venous thromboembolism after total hip replacement. New England Journal of Medicine 1996;volume 335: pages 696-700.

Comp PC et al. Prolonged enoxaparin therapy to prevent venous thromboembolism after primary hip or knee replacement. Journal of Bone and Joint Surgery American volume 2001;volume 83-A: pages 336-45.

Eikelboom JW et al. Extended-duration prophylaxis against venous thromboembolism after total hip or knee replacement: a meta-analysis of the randomised trials. The Lancet 2001;volume 358: pages 9-15.

Geerts WH et al. Prevention of venous thromboembolism. Chest 2001;volume 119: pages 132S-75S.

Hull RD et al. Extended out-of-hospital low-molecular-weight heparin prophylaxis against deep venous thrombosis in patients after elective hip arthroplasty: a systematic review. Annals of Internal Medicine 2001;volume 135: pages 858-69.

Nicolaides AN et al. International Consensus Statement (ICS) 2001. Prevention of venous thromboembolism. International Angiology 2001;volume 20: pages 1-37.

Planes A et al. Risk of deep-venous thrombosis after hospital discharge in patients having undergone total hip replacement: double-blind randomised comparison of enoxaparin versus placebo. The Lancet 1996;volume 348: pages 224-8.

Turpie AGG et al. Fondaparinux vs enoxaparin for the prevention of venous thromboembolism in major orthopedic surgery. Archives of Internal Medicine 2002;volume 162: pages 1833-40

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