A controversial study estimates the risk of venous thromboembolism, or serious blood clot, at 1% for those undergoing knee replacement and .5% for those receiving a new hip during the few days they recuperate in the hospital after surgery.
The authors, Jean-Marie Januel and colleagues from Lausanne University Hospital in Switzerland and co-authors in France and Canada, used data from 47 studies, most of them randomized controlled trials.
They suggest that because VTE is the most frequent surgical adverse event besides infections, their rates might be used for quality analysis and hospital benchmarking Additionally, they write, there is no widely accepted estimate of symptomatic VTE risk prior to hospital discharge that might be "conveyed to patients in the informed consent process."
VTEs, which can result in sudden death, are thought to be largely preventable, especially since one in four VTEs occur in patients who had major surgery such as hip and knee replacements.
All of the patients included received recommended prophylactic medications.
But according to Mayo thrombosis expert John Heit, MD, of the Mayo Clinic in Rochester, MN, the study published in Wednesday's Journal of the American Medical Association, is deeply flawed for several reasons, and thus misstates the actual VTE risk. Explaining his reasoning in an opposing clinical review in the same issue, Heit said the risk of VTE extends as long as 91 days after surgery, far beyond the few days the patients remain hospitalized and the period of this study.
In a large California data set from between 1991 and 1993, for example, the 91-day cumulative incidence rates for symptomatic VTE were 2.8% for knee replacement patients and 2.1% for hip replacement patients, he writes.
"The authors did everything correctly," Heit says in a phone interview. "But the study has serious limitations that really make the results difficult to interpret and potentially not all that applicable to current day practice."
The percentages in their study are "too low for the entire period of risk, which is three months after hip replacement and a month and a half after knee replacement. And it's probably too high for the current duration of hospitalization, which is only three or four days. So I don't think they're very helpful for counseling the patient or to be used as a benchmark for quality improvement."
He adds, "I would feel very uncomfortable using the rates from this study in counseling a patient, because I think they (the authors) underestimate the true risk."
Heit says that the other problem with the analysis these researchers produced was that most of the data came from randomized controlled trials, which are structured to exclude patients who are older, and sicker and have multiple co-morbidities, the very patients who might be more likely to have higher rates of VTE.
Additionally, the researchers' report assumed patients remained in the hospital for up to 14 weeks, when today, most patients with hip or knee replacement surgery are discharged after the third or fourth postoperative day, Heit says.
The issue is further confused by statements from the American Academy of Orthopaedic Surgeons, which says that for patients with total hip replacement, 7% develop deep vein thrombosis and .3% develop a pulmonary embolism within 90 days of surgery. For total knee replacement patients, .9% develop deep vein thrombosis and .3% develop a pulmonary embolism within 90 days of surgery.
Heit says that the issue remains extremely controversial "because there's such a lack of good data on what is most effective, and what's most safe."