Leg in a cast: When does it make sense to use injections for blood clot prevention?

Photo of a woman in the hospital with crutches
Creatas Images / Creatas / Thinkstock

If someone has their leg in a plaster cast or brace and can’t move it for a long period of time, they are at increased risk of deep vein thrombosis. Injections to prevent blood clots are then recommended. In all other cases, getting back on your feet again as soon as possible is enough.

Sometimes a leg needs to be kept still (immobilized) for a while, for instance because of a bone fracture or surgery on a foot, ankle or lower leg. If you wear a plaster cast or brace for several days or weeks, the blood flow through your veins is slower than if you can move normally. This increases the risk of a blood clot (thrombus) forming in a leg or pelvic vein. Blood clots may end up blocking veins, preventing blood from flowing through them properly. This is known as deep vein thrombosis (DVT).

DVT usually goes unnoticed and dissolves on its own. But some cause symptoms such as red skin, swelling and pain. DVT can become dangerous if the blood clot breaks away from the vein and travels through the blood system into the lungs, causing pulmonary embolism. Luckily, this is very rare, though.

Options for preventing thrombosis

There are several ways to lower the risk of DVT. The most important thing is to get up and get moving again as soon as possible. But you should also take care not to disrupt the healing process by putting strain on the leg too soon.

One way to lower the risk of DVT is to wear compression stockings, at least on the healthy leg. These special stockings apply pressure to the leg, helping the veins to carry the blood back to the heart faster.

Medication that reduces the clotting ability of the blood is another option. The drugs most commonly used for this purpose are known as heparins. They are injected into the skin (subcutaneously). There are two types of heparin: “low-molecular-weight” heparin (LMWH) and “unfractionated” heparin. LMWH only needs to be injected once a day, whereas unfractionated heparin needs to be injected two to three times a day. People who aren’t allowed to move their leg usually use LMWH. If they are recuperating at home, they can inject it themselves.

One possible side effect of heparin injections is bleeding. But this is usually only minor bleeding at the site of injection, sometimes visible as bruising. A number of things can increase the risk of bleeding. These include stomach ulcers, a case of bleeding in the last few months, and taking anticoagulants such as acetylsalicylic acid (the drug in medicines like Aspirin). The risk of bleeding is somewhat higher in men than in women, and generally increases with age. The bleeding is very rarely so bad that a blood transfusion is needed, and very rarely affects vital organs.

Heparin isn’t suitable for people who, for instance, have a stomach ulcer or have had serious bleeding in the past few weeks or months.

Research on preventive medication

Researchers from the wanted to find out how effectively low-molecular-weight heparin can prevent DVT in people who have their lower leg in a plaster cast or brace. They found six studies involving a total of 1,490 participants. Half of the participants were given heparin injections, and the other half were given a fake medicine (placebo) – for as long as their leg was immobilized.

After the Cochrane analysis was completed, a good-quality Dutch study on the same topic was published. It is the biggest study on injections for the prevention of blood clots so far, involving more than 1,400 participants. Most of them were being treated for an ankle or foot fracture, and had to wear a plaster cast or brace for five weeks on average.

Current research results

The Cochrane researchers found that injecting medication for the prevention of blood clots can lower the risk of deep vein thrombosis:

  • 25 out of 1,000 people who didn’t have heparin injections developed DVT with noticeable symptoms.
  • 3 out of 1,000 people who had heparin injections developed DVT with noticeable symptoms.

In other words: If 1,000 people who have to wear a plaster cast or brace on their lower leg have heparin injections, 22 cases of deep vein thrombosis are prevented.

The large Dutch study didn’t come to the same conclusions, though: Heparin injections weren’t found to offer any clear advantages. But the people in the Dutch study had a lower risk of deep vein thrombosis to start off with – only 11 out of 1,000 of those who didn’t have heparin injections developed DVT.

When are injections for the prevention of blood clots recommended?

The medical associations in Germany got together to develop guidelines on the prevention of venous thrombosis (thrombosis in veins). They only recommend injections for the prevention of blood clots in people with an increased risk of DVT. The risk is considered to be increased if at least one of the following risk factors is present:

  • Previous venous thrombosis
  • A particular blood clotting disorder
  • Cancer
  • Older than 60 years
  • Obesity ( of more than 30)
  • Chronic heart failure or a previous

People who don’t have any risk factors don’t need to have injections for the prevention of thrombosis. Moving their leg again as soon as possible is enough in their case.

Arbeitsgemeinschaft der Wissenschaftlichen Medizinischen Fachgesellschaften (AWMF). S3-Leitlinie Prophylaxe der venösen Thromboembolie (VTE). October  2015. (AWMF-Leitlinien; Volume 003 - 001).

Chapelle C, Rosencher N, Jacques Zufferey P, Mismetti P, Cucherat M, Laporte S et al. Prevention of venous thromboembolic events with low-molecular-weight heparin in the non-major orthopaedic setting: meta-analysis of randomized controlled trials. Arthroscopy 2014; 30(8): 987-996.

Encke A, Haas S, Kopp I. Prophylaxe der venösen Thromboembolie. Dtsch Arztebl Int 2016; 113(31-32): 532-538.

Sachdeva A, Dalton M, Amaragiri SV, Lees T. Graduated compression stockings for prevention of deep vein thrombosis. Cochrane Database Syst Rev 2014; (12): CD001484.

Testroote M, Stigter WAH, Janssen L, Janzing HM. Low molecular weight heparin for prevention of venous thromboembolism in patients with lower-leg immobilization. Cochrane Database Syst Rev 2014; (4): CD006681.

van Adrichem RA, Nemeth B, Algra A, le Cessie S, Rosendaal FR, Schipper IB; POT-KAST and POT-CAST Group. Thromboprophylaxis after Knee Arthroscopy and Lower-Leg Casting. N Engl J Med 2017; 376(6): 515-525.

IQWiG health information is written with the aim of helping people understand the advantages and disadvantages of the main treatment options and health care services.

Because IQWiG is a German institute, some of the information provided here is specific to the German health care system. The suitability of any of the described options in an individual case can be determined by talking to a doctor. informedhealth.org can provide support for talks with doctors and other medical professionals, but cannot replace them. We do not offer individual consultations.

Our information is based on the results of good-quality studies. It is written by a team of health care professionals, scientists and editors, and reviewed by external experts. You can find a detailed description of how our health information is produced and updated in our methods.

Comment on this page

What would you like to share with us?

We welcome any feedback and ideas. We will review, but not publish, your ratings and comments. Your information will of course be treated confidentially. Fields marked with an asterisk (*) are required fields.

Please note that we do not provide individual advice on matters of health. You can read about where to find help and support in Germany in our information “How can I find self-help groups and information centers?

Created on March 23, 2017
Next planned update: 2021


Institute for Quality and Efficiency in Health Care (IQWiG, Germany)

How we keep you informed

Follow us on Twitter or subscribe to our newsletter or newsfeed. You can find all of our films online on YouTube.