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Surveillance for Venous Thromboembolic Disease After Total Knee Arthroplasty

Berry, Daniel J., MD

Clinical Orthopaedics and Related Research®: November 2001 - Volume 392 - Issue - p 257-266
SECTION I SYMPOSIUM: The Papers Presented at the Knee Society Meeting 2001
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The value of deep venous thrombosis screening after total knee arthroplasty is controversial. The purpose of the current study was to examine the value of routine surveillance for venous thrombosis after total knee arthroplasty done with modern operative and perioperative treatment. Computerized search engines were used to identify papers published between 1985 and July 2000 relevant to the purpose of the study. Papers that met the inclusion criteria for review were categorized as follows: the frequency of deep venous thrombosis; the natural history of deep venous thrombosis; the accuracy of screening methods for venous thrombosis; and efficacy of screening in reducing morbidity attributable to venous thromboembolism after total knee arthroplasty. Several studies have shown a low complication rate related to venous thromboembolic disease when compression ultrasound is used for screening as part of a clinical algorithm after knee arthroplasty. However, the only large prospective randomized trial evaluating ultrasound screening failed to show a reduction in morbidity with a surveillance protocol. The benefits of surveillance depend on factors specific to each surgeon’s practice including the type and duration of venous prophylaxis, the rate of symptomatic and asymptomatic thromboembolic disease associated with that protocol, and the accuracy of screening tests used for surveillance.

From the Mayo Clinic, Rochester, MN.

Reprint requests to Daniel J. Berry, MD, Mayo Clinic, 200 First Street Southwest, Rochester, MN 55905.

The role of routine screening for deep venous thrombosis after total knee arthroplasty is controversial. Advocates argue that routine screening has several potential advantages including detection and treatment of asymptomatic but potentially life-threatening clots and the potential to reduce the number of patients treated with a prophylactic agent after discharge, thereby reducing the cost, inconvenience, and morbidity associated with thromboembolism prophylaxis. 18,31,70 However, routine screening also has some disadvantages including imperfect accuracy of screening tests, the potential of screening to lead to overtreatment of patients who otherwise are asymptomatic, the potential undertreatment of patients with clots that are not detected, and the cost associated with routine screening.

The central question regarding screening remains: With modern perioperative treatment, does routine surveillance lead to a reduction in venous thromboembolism-related morbidity and mortality after total knee arthroplasty? The purpose of the current study was to examine the data that determine the value of routine surveillance for venous thromboembolic disease after total knee arthroplasty.

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MATERIALS AND METHODS

Using computerized search engines, all papers published between 1985 and July 2000 were identified that listed as key words the combination of deep venous thrombosis and knee arthroplasty or the combination of ultrasonography and knee arthroplasty.

From 194 papers that met these criteria, 69 met one or more of the following criteria: (1) the paper reported the sensitivity, specificity, or accuracy of a screening method for deep venous thrombosis after total knee arthroplasty; (2) the paper reported the frequency of deep venous thromboembolic disease using an accepted screening method after total knee arthroplasty; (3) the paper reported the natural history of venous thromboembolic disease using an accepted screening method after total knee arthroplasty; and (4) the paper reported the efficacy of an accepted screening method as part of a clinical algorithm to reduce morbidity or mortality related to venous thromboembolic disease after total knee arthroplasty. Studies that included, but did not stratify knee operations other than total knee arthroplasty were not included.

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RESULTS

Rate of Venous Thromboembolic Disease after Total Knee Arthroplasty

The rate of asymptomatic venous thromboembolism after total knee arthroplasty is recognized to be much higher than the rate of symptomatic deep venous thrombosis or pulmonary embolism. 39 Asymptomatic venous thrombosis is far more common in the extremity ipsilateral to the arthroplasty. 33 Even with modern methods of venous thromboembolism prophylaxis, the rates of deep venous thrombosis postoperatively as reported in most studies using contemporary surgical and perioperative treatment range from 30% to 55% when venography (Table 1), the most accurate test, is used as an end point. 43 The frequency of venous thromboembolic disease in papers specifically reporting the rate in 100 or more patients with a venogram end point are summarized in Table 1. It is important to recognize the high rate of asymptomatic disease because it has an impact on the value of doing routine screening tests. The precise incidence and location 46,67 of clots after total knee arthroplasty are affected by the type and dose of prophylactic agent(s) 13,17,28,34,38,47,49,60,66 used and by other features of a patient cohort including the frequency of bilateral knee arthroplasties, 44 patient group demographic factors, 30 and aspects of operative 7,41 and perioperative treatment 1,25,60 including type of anesthetic. 27,54 The frequency of venous thromboembolism in a specific surgeon’s practice will have an effect on the efficacy of routine screening procedures in that surgeon’s practice. The incidence of detectable venous thrombosis preoperatively is low in patients who have total knee arthroplasty. 22

TABLE 1

TABLE 1

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Natural History of Venous Thromboembolism After Total Knee Arthroplasty

Clots in the proximal venous system of the lower extremity are known to pose a greater risk for embolization than clots confined to the calf. The risk of embolization from proximal clots can be reduced by treatment with anticoagulation. Woolson 68 showed that 34 of 47 femoral or popliteal clots that formed after total hip arthroplasty or total knee arthroplasty for which the patients were treated with anticoagulants, lysed by an average of 7 weeks, 12 were smaller or unchanged, and only one propagated and embolized. A more controversial but important issue is the frequency with which isolated calf clots that form after total knee arthroplasty propagate proximally or embolize directly from the calf. Oishi et al 48 followed up 41 patients who had an asymptomatic calf clot detected by duplex ultrasonography at Day 4 after total hip arthroplasty or total knee arthroplasty. Seven patients (17%) had a new ultrasonographically-detected proximal thrombosis develop by 14 days after surgery. Of the 34 remaining patients with asymptomatic calf clots who did not receive anticoagulation, the clots in 33 patients remained stable and one progressed at 11 months postoperatively. Barnes et al 3 reported that 18% of deep calf vein clots identified by venogram after total hip arthroplasty or total knee arthroplasty progressed proximally in the absence of anticoagulation. Based on these studies and others there is general consensus that asymptomatic clots confined to the deep veins of the calf are common after total knee arthroplasty, that they can propagate proximally, but that clinically significant propagation or embolization even in the absence of treatment with anticoagulation is not frequent. 40,56 Haas et al 20 reported on 1625 total knee arthroplasties in 1257 patients. They reported that 1.6% of patients with calf clots on venogram had symptoms of pulmonary embolism develop (and 6.9% had positive lung scans) and only 0.03% of patients with no calf clots had asymptomatic pulmonary embolism (2% had a positive lung scan). The risk of pulmonary embolism posed by a calf clot was found to be small, but statistically significant.

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Efficacy of Different Screening Methods

The value of routine screening for venous thromboembolic disease in part is determined by the sensitivity, specificity, and accuracy of the screening methods available. It also is determined by the morbidity and cost associated with each of the available screening methods. Venography is considered the most accurate test to determine whether a patient has a deep venous thrombosis, and is the test to which other screening methods usually are compared. Except for specific study protocols, venography currently is not considered an ideal screening method under most circumstances because of its cost, inconvenience, invasive nature, and potential to cause morbidity. 45,61 Currently, labeled fibrinogen scans are used infrequently, although newer labeled scanning methods have shown promise. 5 Magnetic resonance imaging methods are evolving but have yet to eclipse the accuracy of venography. 32

In the past decade, most interest has focused on noninvasive vascular studies including compression ultrasonography, 16 impedence plethysmography, 42 and color Doppler as screening tools. Neither impedence plethysmography 16 nor color Doppler 3,36,37,53 have proven to be as accurate as compression ultrasonography. A comparison of Tables 1 and 2 suggests venography is a more sensitive test than noninvasive techniques. The accuracy, noninvasive nature, ability to repeat the examination as needed, and relatively low cost have made compression ultrasonography the screening method in which there has been the most interest. Table 3 summarizes the literature comparing noninvasive study methods with venography for detection of venous thrombosis.

TABLE 2

TABLE 2

TABLE 3

TABLE 3

As more experience has been gained with compression ultrasonography, much has been learned about the factors that effect its accuracy. The sensitivity and specificity of ultrasonography are highly technician dependent, and more experience with administering the test has been shown to correlate with greater accuracy. Garino et al 15 reported one technician had a 0% sensitivity in identifying seven venogram-proven proximal clots in 121 patients, and another technician had a 100% sensitivity (and 98% specificity) in identifying five proximal clots in 84 patients. Westrich et al 62 reported that the sensitivity of ultrasound (compared with venography) improved from 75% to 85% and the accuracy of the test improved from 91% to 95% after 2 years of experience by the same ultrasound technician and radiologist. Ultrasonography is a more sensitive test for proximal than distal clots. Most pulmonary emboli after total knee arthroplasty probably originate in the popliteal or femoral venous systems, but pulmonary emboli also have been reported to arise from calf clots after total knee arthroplasty. 19 Ultrasonography also may miss clots in pelvic veins. The fact that ultrasound may not detect calf or pelvic clots is important because this means a negative ultrasound does not ensure that a patient has no risk of pulmonary embolism.

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Ultrasonographic Screening as Part of a Protocol to Reduce Morbidity Associated With Venous Thromboembolic Disease and Treatment After Total Knee Arthroplasty

The results of using ultrasonographic screening for deep venous thrombosis after total knee arthroplasty before hospital discharge as part of a routine patient treatment algorithm have been reported by several authors. 18,31,70 With such protocols, the authors have had a low rate of complications related to venous thromboembolic disease and related to the prophylaxis and treatment of venous thromboembolic disease. However, there is only a small amount of information about whether such a screening protocol reduces the rate of overall morbidity and mortality related to prevention and treatment of venous thromboembolic disease compared with protocols for patient treatment that do not include routine screening for venous thromboembolism. The best information on this subject comes from a prospective, double-blind, randomized, controlled trial in which 1024 patients who had elective total hip arthroplasty or total knee arthroplasty were randomized to receive bilateral compression ultrasound tests or sham bilateral compression ultrasound tests before hospital discharge. 2,51 Patients routinely were treated with Coumadin for venous thromboembolism prophylaxis while in the hospital and were followed up for 90 days after the operation. Patients who had asymptomatic clots at discharge were treated with anticoagulation and patients without clots had the Coumadin discontinued at discharge. In the group of 518 patients who were screened, asymptomatic proximal clots were identified (and treated) in 13 patients (2.5%). In the same group, four additional patients ultimately had a symptomatic proximal deep venous thrombosis develop and one patient who had been treated with anticoagulation had a major bleeding episode; the event rate in the group that was screened therefore was five of 513 or 1%. In the group of 506 patients who had a sham ultrasound, three patients had symptomatic proximal clots develop and two had nonfatal pulmonary emboli develop; the event rate in the patients in the sham group was five of 506 or 1%. The authors concluded that with routine Coumadin prophylaxis, the rate of venous thromboembolic disease is sufficiently low that the use of screening ultrasound is not justified.

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DISCUSSION

The information summarized in the aforementioned sections shows that venous thromboembolic disease after total knee arthroplasty is common, usually asymptomatic, most commonly is present in the calf but also can involve the proximal venous system, and can be detected in many cases, particularly for proximal clots (that seem to represent the greatest embolism risk) using noninvasive tests.

The known potential of asymptomatic proximal clots to lead to pulmonary emboli in combination with the development of noninvasive, widely available, screening tests for asymptomatic clots has provided the rationale for proposing routine surveillance for deep venous thrombosis after total knee arthroplasty. The potential value of surveillance is that it might reduce venous thromboembolismrelated morbidity and mortality by two mechanisms. First, screening could identify patients with clots and allow treatment of clots before they become symptomatic or lead to embolism. Second, screening could identify patients without clots and allow them to safely discontinue pharmacologic venous thromboembolic prophylaxis and thereby avoid the risk, cost, and inconvenience associated with longer use of prophylactic agents. At the same time, routine screening has some potential disadvantages including the potential to lead to undertreatment or overtreatment of some patients and the cost associated with the test.

To date, the best information available on the value of screening comes from a large, prospective, randomized controlled trial comparing compression ultrasound with a sham test before hospital discharge. 2,51 The study failed to show an advantage of routine ultrasound screening in reducing the rate of adverse events related to venous thromboembolism or its prevention and treatment. The study provides a strong argument against the routine use of screening after total hip arthroplasty and total knee arthroplasty. However, to interpret the study properly, and to place it in context, the limitations of the study must be understood. The study is only one cohort of patients treated by one group of surgeons with a specific perioperative protocol. In the study, all patients routinely were treated with Coumadin during hospitalization and the rate of proximal deep venous thrombosis was low. The lower the rate of disease, the lower the likelihood that routine screening will be of value. Additionally in that study, the mean length of hospitalization was 9 days, considerably longer than that commonly reported for patients who currently are treated in North America. The study included patients who had hip and knee arthroplasty but does not distinguish between them. Importantly, the rate and location of venous thromboembolic disease and the natural history of the disease in patients who had hip and knee arthroplasty are not identical. Interpretation of this prospective randomized study should be made with this significant limitation in mind.

The value of routine screening is determined by many factors including the frequency of asymptomatic clots in a patient group; the risk of embolization from those clots if the patient does not receive specific treatment other than the routine prophylaxis being used; the rate of complications associated with treatment of asymptomatic clots; the sensitivity and specificity of the screening test being used; and the rate of complications associated with routine prophylaxis of all patients after hospital discharge. If a specific perioperative protocol is associated with a relatively high rate of asymptomatic proximal clots, screening may be of greater value. Similarly, if the routine venous thromboembolism prophylaxis program in place provides little protection against asymptomatic clots (if pharmacologic prophylaxis routinely is stopped after a brief hospital stay) the value of screening also might be greater. Likewise, if the routine venous thromboembolism program in place for all patients leads to a relatively high rate of complications then the value of screening (and the value of being able to spare many patients a longer duration of routine prophylaxis) would be greater. However, if the treatment protocol for asymptomatic clots identified by screening has a high complication rate, the relative benefit of screening is less. Finally, if the screening test used in a specific hospital is not sufficiently sensitive, some patients may be undertreated whereas if the screening test is not sufficiently specific, some patients may be overtreated.

The value of routine surveillance for deep venous thrombosis at the time of hospital discharge after total knee arthroplasty is unproven, and is cast into doubt by the best study on the subject. 2,51 However, the value of a surveillance protocol in reducing venous thromboembolic disease-related morbidity and mortality, and the cost-effectiveness of such a protocol probably depends on many features of a specific hospital and surgeon’s practice and perioperative protocol. These include the type and duration of venous thromboembolism prophylaxis in routine use, the rate of asymptomatic and symptomatic venous thromboembolic disease associated with that protocol, and the accuracy of the screening tests used for surveillance.

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        Section Description

        Richard S. Laskin, MD; Cecil H. Rorabeck, MD; William Healy, MD; and Robert Barrack, MD, Guest Editors

        © 2001 Lippincott Williams & Wilkins, Inc.