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Blood clots after joint replacement are one of the first worries patients raise once they know hip or knee surgery is ahead. Here is the honest answer I give across the desk: the risk is real, but it is small, and we plan for it from the very first day.
There is also a strange piece of history behind how we prevent these clots. One of the most widely used blood thinners, warfarin, started out as rat poison. That fact tends to get a patient’s attention, so let me explain what it means for you.
After more than twenty years performing hip and knee replacement at the Bone and Joint Institute of Tennessee in Franklin, including anterior-approach hip replacement, muscle-sparing subvastus knee replacement, and robotic-assisted surgery with the Mako® system, I have learned that a calm, clear explanation does more good than vague reassurance. So here is the full picture.
What does joint surgery have to do with rat poison?
Warfarin, a common blood thinner, was first developed and sold as a rodent poison in the 1940s and 1950s. At high doses it caused rats to bleed. Researchers then found that at a carefully controlled human dose it safely thinned the blood and prevented dangerous clots.
Today warfarin is one of several anticoagulants (the medical word for blood thinners) approved by the Food and Drug Administration and used safely by millions of people. The same property that made it a poison at one dose makes it a clot-preventing medicine at another. The dose is everything.
I share this story for a reason. A blood thinner is not something to fear. It is a tool we use on purpose, in a measured amount, to protect you during the weeks when your clotting risk is highest.
Why are blood clots after joint replacement a real concern?
Major hip and knee surgery raises clotting risk for three reasons that doctors group together as Virchow’s triad: slower blood flow while you rest and heal, irritation of the vein walls during surgery, and a natural tendency for blood to clot more readily after any operation.
A clot that forms in a deep leg vein is called a deep vein thrombosis, or DVT. The danger is that a piece can break off and travel to the lung, which is called a pulmonary embolism, or PE. A large PE can be life threatening, which is why prevention matters so much.
The good news is that these events are uncommon, and we have reliable ways to lower the odds. That is the balance I want every patient to hold in mind: low risk, not no risk.
How common are blood clots after joint replacement?
Symptomatic blood clots after joint replacement are diagnosed in about 2 to 4 percent of patients. In one analysis of more than 150,000 knee replacements, a pulmonary embolism occurred in fewer than 1 percent of cases. Even with the best care, national data put the risk of DVT near 3 percent and PE near 1.5 percent.
Knee replacement tends to cause clots early, with most symptomatic events in the first three weeks. Hip replacement carries a slightly higher chance of a clot in the larger veins, and those events can show up several weeks after you leave the hospital. Either way, your highest-risk window is the first two weeks, and you stay at some risk for roughly three months.
How long do blood clots after joint replacement stay a risk?
The risk of blood clots after joint replacement is greatest from day two through day ten, then tapers off. We usually continue some form of prevention for several weeks, and I tell patients to stay alert to warning signs for about three months. That timeline is why the medicine and the movement do not stop the day you go home.
What are the warning signs of a blood clot after surgery?
The signs fall into two groups: a clot in the leg and a clot in the lung. Learn both before surgery so you are not guessing during recovery.
Signs of a clot in the leg (DVT)
- New or worsening swelling, usually in one calf or thigh, that does not settle with elevation
- Deep pain, cramping, or tenderness in the calf that is not explained by your incision
- Skin that is warm, red, or discolored over the painful area
- A feeling of tightness or a pulled-muscle ache that keeps getting worse
Signs of a clot in the lung (PE)
- Sudden shortness of breath or trouble catching your breath
- Chest or upper back pain that gets worse with a deep breath
- A new cough, sometimes with a small amount of blood
- A racing heartbeat, lightheadedness, or fainting
Here is my rule for patients: leg symptoms mean call my office the same day. Breathing or chest symptoms mean call 911 or go to the nearest emergency room. Do not wait to see if it passes.
Is my pain normal, or could it be a blood clot?
Normal recovery pain is expected, and it follows a pattern. It sits around your incision and the joint itself, it eases with ice and elevation, and it slowly improves week by week. Mild swelling and warmth near the cut are part of healing.
A blood clot behaves differently. The pain often comes on suddenly or keeps worsening, it sits in the calf or thigh rather than at the incision, and the swelling does not improve when you raise your leg. When something feels out of step with the steady progress you expected, that is your signal to call.
Who is at higher risk for blood clots after joint replacement?
Anyone can develop a clot, but certain factors raise the odds. Knowing yours helps us tailor your prevention plan.
- A personal or family history of blood clots
- Older age and a higher body weight
- Smoking
- Certain cancers, or hormone and birth control medicines
- Heart or lung conditions such as congestive heart failure or chronic obstructive pulmonary disease
- Slow movement or a long stretch of bed rest after surgery
If several of these apply to you, I do not see that as a reason to avoid surgery. I see it as a reason to be more deliberate about your blood thinner, your compression, and how soon we get you walking.
5 safe steps to lower your risk of blood clots after joint replacement
Most clot prevention is simple, and you do most of it yourself. These are the five steps I ask every patient to follow.
- Take your blood thinner exactly as prescribed. Whether it is aspirin, an injection, or an oral medicine, do not skip or stop a dose without calling us first.
- Get up and move early. We have most patients walking the day of surgery. Movement keeps blood from pooling in your legs, which is the single most effective thing you can do.
- Use your compression as directed. Compression stockings and pump devices keep blood moving in the deep veins. Wear them on the schedule we give you.
- Do your ankle pumps and exercises. Simple foot and ankle movements several times an hour act like a pump for your veins, even while you rest.
- Stay hydrated and break up long sitting. Drink fluids and avoid sitting still for hours. On any car or plane trip, stop to walk and flex your feet.
Before surgery, two more steps help: stopping smoking and reaching a healthier weight both lower clot risk. My team in Franklin and our patient resources walk you through all of this well ahead of your date.
What blood thinners are used after joint replacement?
There is no single right medicine for everyone. We match the choice to your clot risk, your bleeding risk, and your other health needs. The common options include:
- Aspirin. For many lower-risk patients, aspirin is enough and is easy to take.
- Direct oral anticoagulants. These newer pills are taken once or twice a day and usually need no routine blood testing.
- Low molecular weight heparin. A short-acting injection under the skin, sometimes given at home for a set number of days.
- Warfarin. The medicine with the rat poison history. It works well but needs regular blood checks and some attention to diet, so we reserve it for specific situations.
Whatever we choose, the goal is the same: thin the blood just enough to stop a dangerous clot, without raising your bleeding risk more than necessary. We review the plan with you before you ever leave the hospital.
When should I call Dr. Calendine’s office?
Call our Franklin office at (615) 791-2630 the same day if you notice new calf or thigh swelling, deep leg pain that is not explained by your incision, or skin that is warm and red over a sore spot. For sudden shortness of breath, chest pain, or coughing up blood, call 911 right away.
If you are weighing hip or knee surgery and want a clear, plain-language conversation about your own clot risk and how we manage it, I would be glad to meet you. You can request a consultation with Dr. Calendine online, or call our office. We care for patients across Franklin, Nashville, Columbia, and the wider Middle Tennessee area.
Disclosure: Dr. Calendine serves as a paid consultant to Stryker for hip and knee implant design and the Mako robotic surgical platform. This article is educational and reflects general clinical guidance, not a product endorsement.
Medical disclaimer: This article is for general education only and is not a substitute for personalized medical advice. Always follow the guidance of your own surgeon and care team. If you think you may have a blood clot, seek medical care promptly. For breathing or chest symptoms, call 911.
References
- White RH, Henderson MC. Risk factors for venous thromboembolism after total hip and knee replacement surgery. Curr Opin Pulm Med. 2002;8(5):365-371.
- Hilliard I, Stead TS, Banerjee A, Hua Y, Ganti L. Mind the clot: predictors of pulmonary embolism after total knee arthroplasty, an analysis of 150,119 cases. Orthopedic Reviews. 2025;17.
- Mosher H, Remer HB, Osondu CU, et al. Current rates and trends of venous thromboembolism after total hip and knee arthroplasty: an updated analysis utilizing the NSQIP database. Arthroplast Today. 2025;33:101737.
- National Blood Clot Alliance. Prevention and treatment of blood clots after hip and knee replacement surgery. Stop the Clot.
- American Academy of Orthopaedic Surgeons. Deep vein thrombosis. OrthoInfo.
