The People's Perspective on Medicine

How To Prevent Blood Clots After Knee Replacement

Over one million people will get a hip or knee replacement operation this year. Blood clots after surgery are dangerous. Can aspirin prevent blood clots?

Hip and knee replacement surgeries are growing at an extraordinary rate. The American Academy of Orthopedic Surgeons (AAOS) reports that in 2014 there were 370,770 hip replacement surgeries and 680,150 total knee replacements (2018 AAOS Annual Meeting)  It’s a growth industry. That’s because aging baby boomers want to stay active. Joint replacement offers them a second chance to keep moving without unbearable pain. But there is a risk. Blood clots in leg veins are common after surgery. But there is a way to prevent blood clots and potentially life-threatening complications.

Blood Clots After Knee Replacement Are Dangerous

Blood clots are always serious. It has been reported that symptomatic and asymptomatic blood clots after hip or knee replacement surgery can reach as high as 60%. That is if proper prophylaxis is not implemented (Arthroplasty Today, Sept. 2018).

When a blood clot forms in the deep veins of the legs it can break loose and lodge in the lungs. That is called a pulmonary embolism (PE). There is a significant risk of death when that happens. That’s why it is critical that doctors take action to prevent blood clots. A new study suggests that aspirin is just as good as pricey anticoagulants to prevent blood clots

A Reader Shares What Happened Without Prevention:

Q. I had a full right knee replacement. Within 24 hours post-surgery, I had blood clots in both calves. I was immediately put on Coumadin.

I was changed from Coumadin to Xarelto after a few months and have been on it ever since, along with a daily low dose aspirin.

I have no idea what Xarelto and daily aspirin are doing to my body. All my physicians say that I must stay on it for the rest of my life because once you have a blood clot, you are then at higher risk for more.

How to Prevent Blood Clots:

A. We are shocked that you did not receive medicine to prevent blood clots prior to or immediately after your knee replacement. That is now considered standard practice.

A study published in JAMA Surgery (online, Oct. 17, 2018) demonstrated the importance of prevention when planning a knee replacement. The researchers tracked 41,537 Michigan patients who underwent knee replacement surgery (aka total knee arthroplasty or TKA). They all received some sort of anticoagulant treatment. It was administered either one day before surgery, the day of surgery or one day after surgery.

Aspirin Was “Noninferior” to Anticoagulants

Surprisingly, aspirin was just as effective as drugs like rivaroxaban (Xarelto), warfarin (Coumadin) or low-molecular-weight heparin. Doctors have a strange (and to us convoluted) way of saying that. They love to use the word noninferior. The authors concluded that:

“In this study of patients undergoing TKA [total knee arthroplasty], aspirin was not inferior to other anticoagulants in the postoperative rate of VTE [venous thromboembolism or blood clots in veins] or death.”

In normal English, they found that regular old aspirin was comparable to anticoagulant drugs such as the aforementioned Xarelto, apixaban (Eliquis), argatroban (Acova), edoxaban (Savaysa) or dabigatran (Pradaxa).

They go on to praise aspirin:

“There are several reasons to prefer using aspirin for VTE prophylaxis in the appropriately screened patient. Aspirin administration is simple, safe, and does not require monitoring…Aspirin is also much less expensive. The reported cost for a 30-day supply of rivaroxaban is approximately $379 to $450, and that of LMWH [low-molecular-weight heparin] is estimated at $450 to $890. Warfarin costs a few dollars for a 30-day course, but with monitoring considered, the cost approaches that of the other anticoagulants. In contrast, aspirin costs approximately $2 per month, and no monitoring is needed.”

The Bottom Line:

The most important sentence in this study for people undergoing knee replacement treatment is:

“The results emphasize the need for chemoprophylaxis vs no prophylaxis to reduce the risk of VTE, given the dramatically higher odds of a VTE in the group without prophylaxis.”

What that means is that anyone undergoing knee replacement surgery should receive preventative treatment with an anticoagulant. That will reduce VTE or venous thromboembolism or blood clots in veins in the legs. If we are to believe this research, aspirin would be as effective as other anticoagulant medications.

For This Reader:

You may have to continue on an anticoagulant indefinitely. This is something your doctor will need to review periodically since all anticoagulant medications pose a risk of bleeding.

Share your own story about hip or knee replacement. How did it go? Did you have any complications. Let others benefit from your experience in the comment section below.

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About the Author
Joe Graedon is a pharmacologist who has dedicated his career to making drug information understandable to consumers. His best-selling book, The People’s Pharmacy, was published in 1976 and led to a syndicated newspaper column, syndicated public radio show and web site. In 2006, Long Island University awarded him an honorary doctorate as “one of the country's leading drug experts for the consumer.” .
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I had a hip replacement in August 2013 and seemingly had no complications and an easy recovery. In Feb. 2017, I had two strokes with no warning and no “markers” for a stroke. I wonder, as do friends, if the errant clots had been hovering in my body for those two and a half years?


As a hip and knee replacement specialist, we specifically try to avoid any anticoagulants prior to surgery due to the greatly increased risk of severe bleeding. This dramatically increases the risk of not only requiring a blood transfusion (which should be a rare occurrence after an elective joint replacement) but also a large hematoma may result, greatly increasing the risk of wound healing issues and infection. This can lead to loss of the joint, limb, or life!

Not only was this response incorrect but also inflammatory. Unless the patient has a particular predisposition or known history of blood clots, we would never place them on anticoagulant medications prior to their surgery. In all likelihood, this patient was treated entirely appropriately by their surgeon. Unfortunately, blood clots are a known risk of any surgery and can occur even while on anticoagulants. The risks of aggressive preoperative anticoagulation are well documented and outweigh the potential benefit in the typical patient.

What about high dose fish oil? My naturopath is suggesting this instead of aspirin or Xarelto,etc. for a hip replacement I am planning to have in December. I am also in the process of using alternative treatments for cancer. I would prefer fish oil to aspirin, and aspirin to Xarelto.

When I had knee replacement 9 years go, I was put on Warfarin after surgery. A DNA test was not done prior to the surgery. If it had been, the doctor would have found that my metabolism does not metabolize Warfarin. Twice during the administration of Warfarin, I reached near hemmorhage level, and Warfarin had to be stopped for a few days.

I’m telling all my friends to look at all possibilities of therapy and exercise before replacement. Mine was done in March ‘18 and I have yet to not have pain or swelling after doing any exercise or stretching or standing. The other knee was to be replaced as well and now it’s not giving me problems ( scared it into preforming) so I’m keeping him. My pain and swelling seems to be muscular .
My Dr. did put me on aspirin after the surgery with no problems.

At the age of 75 years, I had bilateral total knee replacement(s) approximately 14 months ago. I was given an injection of a blood thinner almost immediately after surgery and once daily for about a week after that. Once I was fairly mobile and having PT daily, I no longer needed the blood thinner infusions because I was very actively continuing with 3X/day PT exercises at home for about 2 weeks. After that, I had 6 weeks of twice weekly PT sessions at the rehap facility, all the while keeping up with the 3X/day on my own. After 10 days of being off my ‘preventative’ (for heart issues) of one 81mg ASA daily before and after the surgery, I am now back to the ASA schedule of once daily.

I am presently on Coumadin for a bold clot that developed from non surgical causes several years ago. Would it be just as effective for me to start Asprin and stop taking Coumadin?

Only your physician can make that determination!

What would be best dosage for ASA therapy to prevent clots?

I had knee replacement in May 2018. I was told that any infection can go to the knee replacements. The day after I had knee replacement, I started therapy. I went to a rehab center for 10 days, had therapy 3 times a day. I was given pain meds. After that I had 6 wks of home therapy and 10 wks of therapy a therapy center. My Dr. told me all the risks way before surgery. If you do not move you will get blood clots.

I would love to know the answer to this question as well. Doctors only want you on expensive blood thinners!

I am 68 and have had both my knees replaced, one at a time in 2013. I was given Coumadin after the first knee, and yes, it required frequent checks. For the second knee, they prescribed aspirin. It worked just as well as the coumadin (no blood clots either time) and was much less involved. By the way, I went from agonizing knee pain that I’d had for decades to literally ZERO knee pain EVER. I now easily hike 5+ miles in hilly terrain with no problem whatsoever.

An aside, but a really important suggestion for anyone who plans on having a knee replaced: get in the best possible shape you can BEFORE your surgery. I couldn’t walk much beforehand, but I worked out at a PT facility for up to 3 hours 3 days a week, including 30-40 minutes on a stationary bicycle. Once I left the hospital after the surgeries, I didn’t even have to use a walker, and stopped using a cane after 4 days. The surgeon said he’d rarely seen anyone recover so fast and credited it to my building up my strength beforehand. BTW, it was MY idea to get in shape to reduce recovery time, NOT the surgeon’s. Don’t count on your doctor to tell you to build up your muscles. Just do it!

Kassandra ~

Thanks for this wonderful encouragement. I swim and use an exercycle but have been exercycling much less than I used to. Your comments are a wake-up call to me to get back on that exercycle as a priority daily before having my knees replaced.

Last Wednesday, my wife had ‘revision’ hip surgery, and the Orthopedic surgeon only prescribed 1 x 325 mg of enteric coated aspirin a day. In a previous episode, last year, on the other hip, she was prescribed Lovenax, an injectable blood clot preventative. The cost of the Lovenax was $750, whereas the Aspirin was only just pocket change. So,just maybe there is a movement away for these high cost OAC’s.

I had both knees replaced 5 years ago. I also got my leg muscles strong with walking and stationary biking prior to surgery. I have had no pain after finishing therapy and walk up to 10000 steps a day with climbing 3 floors of steps. I was given blood thinner immediately after surgery but only for a couple of days. I was 75 at the time of surgery.

About “Xarelto, apixaban (Eliquis), argatroban (Acova), edoxaban (Savaysa) or dabigatran (Pradaxa)”:
Following a pulmonary embolism, I have been on Coumadin (Jantovan) since 2008 as they never found the source of the clot, and 2 of my ‘Dedimer’ labs fall on the very high end of normal. My understanding is that some of the drugs listed above (ask your doctor) did not have adaquate ‘reversal drugs’ (if you were in a car accident, bleeding, and need a quick coagulant or needed emergency surgery) as of a year or two ago. On Coumadin, I can get a Vitamin K injection (or two) to stop the bleeding or prepare for emergency surgery. I had a gall bladder ‘attack,’ and although the Dr. wanted my surgery that specific day, they did wait one extra day to make sure my levels were good for surgery. Be sure you are wearing a MEDICAL ALERT bracelet, necklace, something. That’s mega important!!!!!

My opinion is: look at the effects of what aspirin does to your kidneys; then look at the natural products that doe the same thing without the side effects. Do the research, and make sure you get a good one. There are several.

what “natural” products are you referring to??

Warfarin is a narrow therapeutic index drug. Your show would be the ideal venue to discuss what that means and create more informed patients.

In my experience, treating patients with the insurance company-determined generics for Coumadin (warfarin), the source of the generic pills kept changing. This resulted in unintended dose changes. Some of this was insurance company-driven, some was what was available or cheapest for the pharmacy to acquire.

If studies show that Aspirin is close to the efficacy of warfarin when managed by experts in affluent areas with Class B generics, then Aspirin would be safer for many people in poor areas with poor staffing and the cheapest generics.

I am on Coumadin life-long because of Protein S autoimmune problems. I had back surgery, and they used a cage with screws to secure my back. I kept asking them to call my hematologist, and they didn’t. They did not handle my problem appropriately and let me go too long without my anticoagulant. As a result, my lungs filled with clots. I don’t think they should have stopped my Coumadin. Just by the grace of God I am here.

Do you favor a patient receiving medicine to prevent blood clots BEFORE surgery ? I have had DVT and several surgeries since having DVT, including two knee replacements. Still, my doctors never put me on an anti-coagulant before or after surgery. In fact, before surgery, I am always told to not take aspirin, as it will increase blood loss during surgery.

Only your surgeon can make that determination. The study we cited mentioned three options they were tracking:
Administration of anticoagulant medication the day before, the day of or the day after surgery. The surgeon will be able to tell you what she prefers.

I am facing a full knee replacement in 2019. In 1990 I suffered a pulmonary embolism from an ACL surgery of the same knee. I was hospitalized and put on heparin and coumadin. The coumadin lasted four months after my release from the hospital. The blood clot was caused by being nonambulatory and being a smoker (I smoked my last cigarette on the way to the ER). The point I am trying to make is DO NOT SMOKE. It causes contraction of blood vessels and increases the risk of PE.

I made a full recovery and only have a scar on my right lung lobe from a clot. Every time I have a chest x-ray I must tell the radiologist about the scar. From the time I was admitted to the ER to the present, I have had no desire to smoke. I jokingly say that I was hypnotized when I wasn’t looking. But I know that this was divine intervention. To go from 2 1/2 packs a day to none was a gift that I don’t take lightly.

I had a knee replacement in 2014 and developed a DVT a few days after surgery. I was given Warfarin while in the hospital, which was two days, then put on asprin therapy at home. The DVT developed two days after returning home. When I asked the surgeon why he didn’t continue with Warfarin therapy he said that asprin was the “new” therapy after surgery. When I went to the hospital for ultrasound to locate and treat the DVT, the cardiovascular surgeon there just scoffed at the idea of asprin therapy following knee replacement. He put me on Lovenox for a few weeks till my levels were good then Warfarin for three months. The pain and swelling from the DVT was much worst than the knee. I was black and blue and very swollen from my hip to the big toe.

I am so glad you are writing about this subject. The need at my age (70, and very active) to keep away from pills of any kind is very important. Luckily, all my life I have adhered to a healthy way of life, eat organically, exercising daily, and do not take any medications. Please continue to bring us (the public) such information.

I just read an article about Pycnogenol. In a recent study of deep vein thrombosis there were five groups – a control group, two groups given other anti-coagulants, one group given aspirin, and one group given Pycnogenol. The Pycnogenol group cut their risk of recurrent thrombosis and post-thrombosis symptoms by TWO-THIRDS compared to the control group! It out performed the other groups as well. Pycnogenol is already know as a circulation booster. It might also be smart to consider before flying long-distance or taking a long train or car ride, which can increase the risk of deep vein thrombosis, especially if you already have circulation struggles.

I took 2 aspirin a day right after knee surgery and continued on with the aspirin for 8 years. Never bothered my stomach. Did buy the coated ones. But I stopped taking aspirin because arthritis was bothering me in my back so I went on NSAIDs. I ended up with a stroke a year later. Back on 2 aspirin a day, and it’s been 6 years since my stroke. I have not been on any other blood thinners.

I am 84 and have been taking 15 mg of Xarelto for over five years. I bruise easily, and I bleed when I accidentally rub against something. I know I could bleed to death if I am in an accident.
I would love to switch to aspirin. I asked my cardio about aspirin. He didn’t like the idea. I am very healthy and agile.

What about Serrapeptase? Doesn’t have the stomach issues of aspirin?

Great article! Very well written. Easy to understand and very informative.
I do like reading most of the patients’ perspective on the drugs.

My husband has just gone through a second replacement of the same knee. What they don’t tell you is that any infection in your body, caused by teeth cleaning or in my husband’s case a small cut on his foot that looked perfectly normal and he’d only had for a week, goes right to these replacement parts (hips too). And they have to totally remove the part to get rid of infection. That means total removal, months of having no knee (yes you heard that right – you’re in a wheelchair) and then another knee insertion. They tell you ‘this only happens in 1% of the cases’ – which is untrue if unofficial the survey I did in the hospital wing is any indicator. It’s more like 10%. If there had been prior that warning this could happen he could have been spared these surgeries.

Laura ~

THANK YOU for this valuable warning! I’m having dental work done and am aware of the 6-month no-dental program before knee replacements. Your note is enough to make me extra careful. How fortunate your husband is to have you there to help him. I have some qualms about knee surgeries due to some of these issues but am looking forward to eventual relief.

Some times the information coming from the medical community is totally confusing and contradictory. I’ve been diagnosed with Lone Atrial Fibrillation [LAF], and my cardiologist wants me on an oral anti-coagulant [OAC] like Coumadin or Eliquis to prevent potential blood clots, or strokes. They tell me that Aspirin is not sufficient to prevent blood clots, and that it is ‘inferior’ and only just an anti-platelet drug. Now we have this information from JAMA, telling us that Aspirin is ‘NON-inferior’, and is acceptable as an OAC.

What’s a body to do ????

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