Deep vein thrombosis (DVT)

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Deep vein thrombosis (DVT)

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 goes away on its own. But it sometimes causes symptoms such as swelling, pain and red skin in the affected leg. DVT can become dangerous if the blood clot breaks off from the vein and travels though the bloodstream into the lungs, causing pulmonary embolism. Luckily, this is rare.

How can you 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. These drugs are called anticoagulants, with heparin being the most common. Enoxaparin is also one type of heparin, for example. Heparin is injected under the skin. If you are recovering from an injury or surgery at home, you can inject heparin 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. if you are already using blood thinning injections, compression stockings usually don't offer any extra protection.

How effective are heparin injections at preventing thrombosis?

Studies involving nearly 1,500 people looked into out how effectively heparin can prevent DVT in people who have their lower leg in a plaster cast or brace. 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 results show that the injections 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.

What side effects do the heparin injections have?

One possible side effect of heparin injections is bleeding. But this is usually only minor bleedingat 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 targets the platelets in your blood. The signs of HIT syndrome include discoloration or wounds at the injection site and symptoms like fever, shortness of breath and a racing heartbeat.

Deutsche Gesellschaft für Chirurgie (DGCH), Deutsche Gesellschaft für Innere Medizin (DGIM). S3-Leitlinie Prophylaxe der venösen Thromboembolie (VTE). AWMF register no.: 003-001. 2026.

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.

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.

Turner BR, Machin M, Salih M et al. An Updated Systematic Review and Meta-analysis of the Impact of Graduated Compression Stockings in Addition to Pharmacological Thromboprophylaxis for Prevention of Venous Thromboembolism in Surgical Inpatients. Ann Surg 2024; 279(1): 29-36.

Zee AA, van Lieshout K, van der Heide M et al. Low molecular weight heparin for prevention of venous thromboembolism in patients with lower-limb immobilization. Cochrane Database Syst Rev 2017; (8): CD006681.

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

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Created on July 14, 2026

Next planned update: 2029

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

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