- In a retrospective study of more than 5,000 matched pairs of patients who underwent below-knee surgery, there was a three-fold reduction in venous thromboembolism (VTE) among those who received anticoagulant prophylaxis compared with those who did not
- However, patients who received anticoagulation also exhibited a two-fold increase in the relative risk of bleeding adverse events
- Whenever possible, thromboprophylaxis should be reserved only for patient groups deemed to be at high risk of VTE—although reliable data to accurately inform these decisions remain unavailable
Orthopedic surgeons do not have enough data to guide decisions about anticoagulant prophylaxis against venous thromboembolism (VTE) after below-the-knee procedures. In most retrospective studies, prophylaxis was preferentially used for patients deemed at highest risk of VTE, which biased the results. The few randomized, controlled trials have been underpowered to draw firm conclusions.
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In the Journal of Bone and Joint Surgery, a research team led by Christopher W. DiGiovanni, MD, chief of the Foot and Ankle Center at Massachusetts General Hospital, explains why a large retrospective study led them to conclude that thromboprophylaxis is appropriate only for patients at high risk of VTE.
Matched Pairs of Patients
The researchers identified 10,572 adults who underwent orthopedic surgery distal to the knee between August 1, 2005, and July 31, 2015. The researchers used propensity scores to match 5,286 patients who had received primary anticoagulant prophylaxis with 5,286 patients who had not received prophylaxis. Each pair of patients was similar with regard to sex, age, race, location of surgery, comorbidities, history of smoking, and use of contraception or hormone replacement therapy.
Incidence of VTE
The primary outcome was VTE (symptomatic pulmonary embolism and/or deep vein thrombosis) of the lower extremity, iliac vein or inferior vena cava:
- Overall rate: 1.3%
- Rate in patients who received anticoagulation: 0.7%
- Rate in patients who did not: 1.9%
Patients who received anticoagulant prophylaxis had a significant three-times lower risk of developing VTE than those who did receive prophylaxis (odds ratio [OR], 0.38; 95% CI, 0.25–0.56; P < .001).
Incidence of Bleeding Adverse Events (BAE)
The secondary outcome was postoperative bleeding after use of anticoagulant prophylaxis:
- Overall rate: 1.6%
- Rate in patients who received anticoagulation: 2.2%
- Rate in patients who did not: 1.0%
Of the 170 patients who had a bleeding event, 9% required a single blood transfusion, 14% required two or more transfusions, and 6% needed additional surgery because of the bleeding.
Patients who received anticoagulant prophylaxis were at twice the risk of a BAE compared with those who did not receive prophylaxis (OR, 2.18; 95% CI, 1.55–3.09; P < .001).
Indications for Prophylaxis Still Unclear
The relatively low rates of bleeding found in this population are consistent with earlier reports, although the impact of bleeding on patient outcome remains unclear. It is important to note that the morbidity associated with a bleeding event after foot and ankle surgery may be more consequential because of the unforgiving nature of the surrounding soft-tissue envelope in this region.
To balance the protective benefits of prophylaxis against the unintended risk of bleeding, the research team suggests anticoagulant prophylaxis only for patients considered to be at fairly high risk of VTE. One persistent challenge with this perspective as recognized by the authors, however, is that risk-assessment models for VTE have, as yet, only been validated for non-orthopedic procedures.
The authors concluded that a large-scale, prospective study will be required to identify which patients specifically benefit from anticoagulant prophylaxis following surgery below the knee when such treatment efforts are balanced against their associated risks. They are in the process of applying for several national multimillion-dollar grants to fund a prospective randomized North American trial to answer this question definitively, given that the ongoing scientific limitations to optimizing VTE prophylaxis for the below-knee population represent a worldwide problem.
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