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Joint Replacement Surgery and Blood Clots

updated 11/4/20 by Cory Calendine, MD, Orthopedic Surgeon

AskCoryC_MD: My sister had knee replacement and she said her doctor prescribed RAT POISON to her to prevent blood clots after surgery. Could that be true? Is that okay?  - Scared Sister

“Your joint replacement surgery was successful. Now, take this rat poison.” - Joint Replacement Surgeon

Joint Replacement Surgery Associated Risks

Surgery to replace a hip or knee joint is a complex procedure, lasting about an hour to an hour and a half, and comes with some potential complications. One possible complication of joint replacement is the development of blood clots in the lower extremities following surgery. The main concern with developing a blood clot (or deep vein thrombosis, DVT) is the RARE (I said RARE) risk that a blood clot will break free, travel through the bloodstream and block blood flow to the lungs. Although uncommon, this complication—called a pulmonary embolism—can be fatal. Even if a blood clot does not break free, it may cause damage to the valves of the veins. This damage can lead to long-term problems in the legs such as pain, swelling, and recurrent sores.


You can see why we take the PREVENTION of blood clots after surgery very seriously. Without the proper prevention, the risk of blood clots after a hip or knee replacement can be quite high, but with proper prevention the risk is well below 1%. To prevent the occurrence of a blood clot, surgeons typically prescribe a combination of treatment approaches, which may include:

  • Exercise/physical therapy beginning early after surgery and sometimes continuing for several weeks
  • Compression stockings
  • Anti-clotting medicine to reduce the body’s ability to form blood clots

Generic warfarin tablets may come in different shapes, but each strength comes in just one color.

Rat Poison After Joint Replacement

Before each hip and knee replacement I perform, I ask each patient several questions to stratify their individual risk of developing a blood clot after surgery: essentially categorizing them as low risk, medium risk and high risk. I will spare you the long list of questions here, but for example having a prior blood clot yourself would put you in the high risk category. Other factors that affect blood flow in the deep veins and can increase the risk for developing blood clots include:

  • Increasing age
  • Personal or family history of DVT or pulmonary embolism
  • Certain types of malignant cancers
  • Vein disease, such as varicose veins
  • Smoking
  • Using birth control pills or hormone therapy
  • Pregnancy
  • Being overweight or obese
  • Inherited blood-clotting disorder

If you are at a low risk to develop blood clots after surgery, sometimes I just recommend aspirin – that’s right, over-the-counter aspirin – to minimize your risk.

But, if risk factors place you within the medium risk or high risk categories, I might recommend warfarin (also called Coumadin or Jantoven) to be taken for up to four weeks following surgery. Warfarin (first developed in 1948) was designed originally as a rat poison but later approved for medical use in 1954. Warfarin is odorless, tasteless and at high doses would thin the rodent's blood, leading to death. An early recipient of warfarin was US president Dwight D. Eisenhower, who was prescribed the drug after a myocardial infarction in 1955. Despite its widespread use, the mechanism of action of warfarin was not discovered until 1978, when John W. Suttie and colleagues demonstrated that warfarin disrupts vitamin K metabolism by inhibiting the enzyme epoxide reductase. As I understand it, rats have developed a resistance to this drug, and now other drugs are used as rodenticides.

Blood tests are used to safely monitor Warfarin (Coumadin, Jantoven) therapy.

Warfarin is a pill usually taken once a day. The dose must be carefully selected and monitored with blood test twice a week to ensure optimal benefit and limit side effects. Today warfarin (Coumadin, Jantoven) is one of the most widely prescribed oral anticoagulant drugs with around 1-2% of adults in the developed world prescribed the medication. Warfarin is usually safe when well-monitored. The main risk of warfarin therapy is bleeding. While the risk of major bleeding is very low, you need to be aware of potential problems and understand you might even have trouble stopping the bleeding from a minor cut or a nosebleed while on therapy. Your surgeon will review conditions, medications and supplements that can increase your risk of bleeding while on warfarin.

There are other blood thinners besides warfarin that can be used, and it is important to individualize treatment with each patient based on history, procedure and risk factors. My job as an orthopedic physician is first to protect you – from the risks of surgery and from the risks of medication we sometimes have to use to protect you following joint replacement.

Additional Warfarin Information:
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Cory Calendine, MD is an Orthopaedic Surgeon and founding partner of the Bone and Joint Institute of Tennessee at Williamson County Hospital in Franklin, TN. Dr. Calendine is an expert in Joint Replacement, specializing in Hip and Knee Surgery. From diagnosis through treatment, the Orthopaedic Surgical experts at the Bone and Joint Institute use the latest techniques and technology to improve care for people with musculoskeletal problems. For more information, please contact our office or schedule your appointment today.  

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