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

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.

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 vein 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 bloodstream into the lungs, causing pulmonary embolism. Luckily, this is very rare.

Ways to prevent 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.

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 include enoxaparin, for example. Heparins are injected under the skin. If you are recovering at home, you can inject heparins on your own.

Sometimes doctors will prescribe compression stockings as well, at least for the healthy leg. These special stockings apply pressure to the leg, helping the veins to carry the blood back to the heart faster. But one large, high-quality study has now shown that compression stockings don't offer any extra protection if you are already using blood thinning injections.

Research on preventive treatment with medication

Researchers from the wanted to find out how effectively heparins can prevent DVT in people who have their lower leg in a plaster cast or brace. In these studies, half of the participants were given heparin injections, while the other half received an injection without medication in it (placebo). The treatment was continued for as long as the leg was immobilized.

The analysis of six studies involving about 1,470 people shows that injecting medication to prevent blood clots can lower the risk of deep vein thrombosis:

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

In other words: Treatment with heparin prevented deep vein thrombosis in 14 out of 1,000 people who had a cast or a brace. A recent analysis by British researchers has confirmed these results.

Possible side effects of heparin

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. The bleeding is very rarely so bad that a blood transfusion is needed, and very rarely affects vital organs.

Another very rare complication of heparin is HIT (heparin-induced thrombocytopenia) syndrome. This happens when the overreacts to platelets in the blood. The signs of HIT syndrome include severe skin and tissue damage at the injection site and symptoms such as fever, shortness of breath and a racing heartbeat.

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). But there are no general recommendations for people who have an immobilized leg: Some medical societies recommend heparin injections, but the German College of General Practitioners and Family Physicians (DEGAM) does not. They only recommend the injections for people who have a high risk of thrombosis. If your leg is immobilized temporarily, the risk of thrombosis is generally very low.

According to the guidelines, the risk factors for thrombosis include:

  • Previous venous thrombosis
  • Severe blood clotting disorders
  • Cancer
  • Being older than 60 years
  • Obesity ( of more than 30)
  • Chronic heart failure or a previous heart attack

You can talk to your doctor about whether treatment with heparin injections is a good idea for you.

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.

Pandor A, Horner D, Davis S et al. Different strategies for pharmacological thromboprophylaxis for lower-limb immobilisation after injury: systematic review and economic evaluation. Health Technol Assess 2019; 23(63): 1-190.

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

Shalhoub J, Lawton R, Hudson J et al. Graduated compression stockings as adjuvant to pharmaco-thromboprophylaxis in elective surgical patients (GAPS study): randomised controlled trial. BMJ 2020; 369: m1309.

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.

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Updated on May 20, 2021

Next planned update: 2024


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

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