We used a logistic regression model to identify predictors of complication (age, gender, BMI, primary/revision surgery, hip or knee arthroplasty, unilateral or bilateral procedure, dose of enoxaparin, prophylactic use of aspirin or warfarin prophylaxis, and number of comorbidities as potential predictors of complication).
Age, gender, BMI, primary/revision surgery, hip or knee arthroplasty, unilateral or bilateral procedure, dose of enoxaparin, and number of comorbidities were not predictive of overall, major, or minor complications. We found no relationship between the postoperative day on which treatment began and the likelihood of bleeding complications. The overall risk of complications was similar for patients who had taken warfarin and those who had taken aspirin for prophylaxis.
The incidence of in-hospital PE after total joint arthroplasty has remained steady in the last decade [21, 23]. Treatment of this complication presents the arthroplasty surgeon with a dilemma. Anticoagulation in postoperative patients carries obvious risks. However, the need for treatment of PEs, and the reduction in mortality that this treatment affords, has been definitively established [2, 3, 15]. LMWHs have supplanted UFH as the treatment of choice for PE and hold a 1A recommendation from the American College of Chest Physicians for this indication . However, lower prophylactic doses of enoxaparin have been associated with higher rates of wound drainage and reoperation than aspirin or warfarin prophylaxis . The complication rate of therapeutic enoxaparin treatment in the patients undergoing arthroplasty in the early postoperative period has not previously been established. Understanding the risk profile is essential for weighing the risks and benefits of this treatment. The purposes of this study were (1) to delineate the type and incidence of complications associated with the use of enoxaparin at therapeutic doses in close proximity to total joint arthroplasty; and (2) to identify risk factors associated with complications.
The main limitation of this study is lack of a control group that did not receive anticoagulation. The absence of such a control makes direct attribution of complications to the individual treatments less accurate. However, withholding treatment from patients who have had a PE to create a control group would be unethical. Comparison of the cohort in this study to a group without PE would not be appropriate either. Interventions such as blood transfusions are undertaken with different considerations in patients who sustain the cardiovascular stress of a PE. Thus, one could not accurately compare patients without a PE with those with a PE and its associated cardiovascular stress, because treatment would be considerably affected by this variable .
In this cohort of postarthroplasty patients, the incidence of major bleeding complications (10%) was substantially higher than the rates reported for nonsurgical patients, which are 0% to 5% [5, 20, 22, 35]. This difference highlights the unique risks inherent to anticoagulation treatment in patients who have undergone procedures, which include substantial soft tissue dissection and osteotomies. The overall complication rate of enoxaparin treatment is similar to the rate of complications reported for UFH treatment in this setting [18, 26]. However, complications associated with enoxaparin tend to be less severe. In 1989, Patterson et al. reported complications in 35% of postarthroplasty patients treated with UFH from our institution . Forty-one of their 112 patients had anticoagulation stopped as a result of the severity of complications. Only one patient in our cohort required therapy to be stopped. On average, patients treated with enoxaparin had a lower transfusion requirement (by 50%) than those reported for UFH (average 3 versus 1.5 units, respectively). Only one patient treated with enoxaparin required reoperation compared with three patients reported for UFH. Although formal statistical comparisons are unlikely to be valid between two groups treated more than 20 years apart, there appear to be fewer bleeding complications with enoxaparin treatment in patients undergoing modern arthroplasty compared with historic reports of UFH treatment. Surgical site complications, which include wound hemorrhage, have been the most frequently reported complication of enoxaparin prophylaxis  and is the most common complication of therapeutic treatment. Although the majority of these are minor, 8% of patients in the current study had major surgical site bleeding.
Obesity has been identified as a risk factor for surgical site complications with enoxaparin prophylaxis . We did not find that increased BMI correlated with increased risk for any type of complication. Remarkably, increasing dosage of enoxaparin (which would correlate with increased BMI in weight-based dosing) was also not predictive of complications. Shaieb et al. have reported increased complications when prophylactic enoxaparin was begun within 6 hours of surgery and when used in patients undergoing bilateral procedures . Patterson et al. noted a considerable increase in complications when UFH anticoagulation was begun within the first 5 postoperative days . We found no correlation between the time at which treatment was initiated relative to surgery and subsequent complications. Nor were patients who underwent bilateral procedures more likely to have a complication. Complications were equally likely in patients who underwent hip versus knee arthroplasty.
Our study elucidates the complications associated with modern anticoagulation treatment of perioperative PE after major total joint arthroplasty. Therapeutic enoxaparin treatment postoperatively in patients undergoing arthroplasty has a 10% rate of major bleeding complications and a 27% rate of minor complications. Major bleeding complications occur twice as frequently as reported in nonsurgical patients. Complications of enoxaparin tend to be less severe than those associated with intravenous UFH. Obese patients undergoing arthroplasty who receive high doses of enoxaparin are not at greater risk for complications than patients with lower BMIs, and the risk profile is not different for patients who undergo bilateral procedures.
We thank Brett Lenart, MD, and Michael Loeven, BS, for their assistance with data collection.
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