Simple solution, large-scale impact

A medication found in medicine cabinets around the world may be all many patients need to prevent dangerous blood clots after hip and knee replacement surgery.

That is the finding of a landmark Canadian study administered by Nova Scotia Health (NSH) and led by Dr. Sudeep Shivakumar, associate professor and head of the Division of Hematology at Dalhousie University's Faculty of Medicine. 

The study was recently published in the New England Journal of Medicine (NEJM), widely considered the world's leading medical journal. It found that aspirin alone was as safe and effective as a more complex regimen involving the blood thinner rivaroxaban followed by aspirin for preventing potentially life-threatening blood clots after total hip and knee replacement surgery.

"After a total hip or total knee replacement, there is an increased risk of blood clots," explains Dr. Shivakumar. "What we wanted to do with this study is to look at whether aspirin, which is commonly known and inexpensive, can be as good as blood thinners in this situation." 

Answering an important clinical question

Joint replacement surgeries are among the most common surgical procedures performed worldwide. While blood-thinning medications have dramatically reduced the risk of post-surgical blood clots, they can also increase the risk of bleeding complications. Clinicians have long wondered whether aspirin alone could provide the same protection without the added complexity of stronger anticoagulants. 

To find out, researchers launched a large randomized, double-blind clinical trial comparing aspirin alone with a commonly used treatment strategy that begins with rivaroxaban before transitioning to aspirin. 

While the research team was based at Dalhousie, the clinical trial funding was administered through NSH, which played a key role in supporting the study's delivery through 5,300 patients at 15 university-affiliated health centres across Canada. Neither the participants nor the investigators knew which treatment individual patients received during the study, helping eliminate potential bias.

"We were able to show that aspirin alone is as safe and as effective as a strategy using a blood thinner followed by aspirin," says Dr. Shivakumar.

Benefits for patients and health systems

For patients, the findings could help simplify recovery after surgery.

The alternative treatment strategy requires patients to take rivaroxaban for five days before switching to aspirin, a process that can create confusion during an already challenging recovery period. Aspirin, by contrast, offers a simpler, one-drug approach. 

"It gives us some evidence so that we can present options to patients so they can make decisions with their healthcare provider," says Dr. Shivakumar. "Now we have a big study that shows that this option of using aspirin alone is a good one.”

The findings may also have broader implications for healthcare systems. While the study did not include a formal economic analysis, aspirin is widely available and inexpensive compared with many newer blood thinners. 

"Hopefully it would save patients and the healthcare system some money," says Dr. Shivakumar. 

A Canadian collaboration years in the making

The publication marks the culmination of nearly eight years of work.

Planning for the study began in 2018, with funding awarded in 2019 through the Canadian Institutes of Health Research (CIHR). Researchers had hoped to begin recruitment in 2020, but the arrival of the COVID-19 pandemic threatened to derail the project before it started. 

Because the study focused on elective hip and knee replacement surgeries, the widespread cancellation of elective procedures created major uncertainty about whether researchers would be able to recruit enough participants to complete the trial. 

"We didn't know when the world would return to normal, or sort of normal," recalls Dr. Shivakumar. "We didn’t know that we’d get the number of patients in a reasonable amount of time.”  

Recruitment eventually accelerated as surgical programs resumed across the country, allowing the study to move forward. The trial was completed in early 2026 and was published only months later. 

The project was supported entirely through public funding, something Dr. Shivakumar views as particularly significant.

"There was no pharmaceutical or private funding," he says. "It was all through the Canadian Institutes of Health Research." 

From Halifax to the world

Beyond the scientific findings themselves, Dr. Shivakumar hopes the study demonstrates the impact Canadian researchers can have on global healthcare.

"This is really proof that practice-changing research can happen in Canada," he says. "We can contribute with a high-quality study that will give information to people around the world."  

He credits the success of the project to an extensive network of collaborators across the country, including surgeons, research staff, study coordinators, patients, and families who contributed their time and effort over many years. More than 250 research personnel helped support the study across participating sites.

Most importantly, he says, patients made the research possible.

"This study wouldn't have happened without them." 

A milestone publication

Seeing the results published in the New England Journal of Medicine was both professionally rewarding and encouraging.

"The NEMJ is the premier medical journal," says Dr. Shivakumar. "To have our work there shows that they also thought that it was a well-run study that has the potential to change practice." 

The achievement also highlights the calibre of research being conducted at Nova Scotia Health and Dalhousie University.

"I think we really are an amazing institution with the ability to do world-class research," he says. "We can affect people in all corners of the world." 

As the research team looks ahead, its focus is no longer on collecting data, but on ensuring the findings reach the clinicians and patients who stand to benefit from them.

"The bottom line is that we now have evidence that an aspirin-alone strategy is as good and as safe as one involving a blood thinner," says Dr. Shivakumar. "Patients have options, and we now have evidence that can help inform their decisions."