Venous thromboembolism (VTE), which encompasses deep vein thrombosis (DVT) and pulmonary embolism (PE), is one of the most common reasons for readmission following primary hip or knee replacement surgery. However, recent studies suggest that only 0.7% to 0.9% of patients undergoing hip or knee replacements require rehospitalization because of VTE in the first 3 months after surgery. “These surgeries put patients at risk for thromboembolic disease because they affect multiple aspects of Virchow’s triad,” explains Joshua J. Jacobs, MD.

Virchow’s triad consists of hypercoagulability, venous stasis, and injury to the vascular endothelium. All three components of the triad can be present following hip or knee replacement surgery and predispose individuals to thrombosis, according to Dr. Jacobs. “DVT occurs in about 37% of patients following primary hip or knee replacement surgery who have not been treated with prophylactic agents. The rate of clinically symptomatic VTE events is far less, but VTE should be an important concern of orthopedic surgeons performing these procedures.”

New Guidelines on Preventing VTE

Dr. Jacobs chaired a workgroup that updated guidelines from the American Academy of Orthopaedic Surgeons (AAOS) on preventing VTE in patients undergoing elective hip and knee arthroplasty. The guidelines were released on September 24, 2011 and are available for free at www.aaos.org/guidelines. “The AAOS felt it was necessary to update these guidelines for the first time since 2007 because of the increasing availability of study data that impacted the previous recommendations and to maintain inclusion in the AHRQ’s National Guideline Clearinghouse, which requires an update every 5 years,” says Dr. Jacobs. The American College of Chest Physicians has also published guidelines on VTE and prophylaxis, but the AAOS felt it was important to create a focused update that is directed toward orthopedic surgeons. Dr. Jacobs adds that “with more than 1 million of these procedures performed annually in the United States, even a small percentage of VTE complications can translate into a large number of patients at risk.”

Focusing on VTE Prophylaxis

Patients who have had a prior VTE event are at higher risk for a subsequent event following primary total hip or knee replacement, says Dr. Jacobs. “Practitioners need to be aware that these patients may require additional measures to provide adequate prophylaxis.” One of the most important recommendations in the AAOS guideline, according to Dr. Jacobs, is to use pharmacologic agents, mechanical compressive devices, or both to prevent VTE in this surgical population (Figure 1). “Unfortunately, with the evidence available, we were unable to conclude which prophylactic regimens are best when looking at symptomatic PE and death from bleeding, which are the most critical outcomes of all-cause mortality. Most studies performed to date are simply underpowered to address these events.” (see also, Increasing VTE Prophylaxis Adherence)

The AAOS guidelines provide a grading system of recommendations that is based on level of evidence from currently available data. A strong recommendation was backed by at least two high-quality studies, with quality related to a number of factors. A well-executed, randomized clinical trial was considered a high-quality study. Two moderate-quality studies were required for a moderate grade, and a minimum of two low-quality studies were needed for a weak grade (figure 2). An inconclusive grade was given when studies failed to meet these thresholds or were conflicting. A consensus recommendation was made when published evidence was lacking and where the intervention was of minimal to no risk and of low cost, Dr. Jacobs says.

To illustrate how the grading process should be interpreted, Dr. Jacobs points to the moderate recommendation that patients discontinue antiplatelet agents before surgery. “Multiple high-quality studies addressing antiplatelet agents before surgery focus on cardiac surgery rather than hip and knee operations, so the recommendation is downgraded to moderate,” he says. “On the other hand, no studies have addressed whether early mobilization following hip and knee arthroplasty is truly effective. Reason, however, would suggest that early mobilization would be of benefit to patients because it’s safe and addresses an important component of Virchow’s triad. Hence, we gave this recommendation a consensus grade.”

Future Research on Critical Outcomes

The updated AAOS guidelines have identified several critical outcomes that physicians should consider when deciding on management strategies for patients undergoing these procedures. These include all-cause mortality, death from bleeding, death from PE, periprosthetic joint infection, reoperation due to bleeding, reoperation for any reason within 90 days of surgery, and symptomatic PE. “Currently, we’re frustrated with the lack of high-quality studies addressing these critical outcomes of interest,” says Dr. Jacobs. “Such studies have either not been conducted or are not adequately powered to address outcomes because of the rarity of VTE events. Although these investigations would be complex and expensive, they may provide much-needed information that can be beneficial in the future.”

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