The Risk of Venous Thromboembolism in Non–Large-Joint Surgeries

ABSTRACT

The risk of venous thromboembolism, particularly deep venous thrombosis, after knee arthroscopy, surgically assisted arthroscopy, or treatment of lower extremity fracture may be substantial in patients with factors known to increase the risk of postoperative thromboembolism. Few prospective studies have examined the effect of prophylaxis in these patient populations. However, results suggest that routine administration of a low-molecular-weight heparin reduces the rate of deep venous thrombosis in such patients. Additional clinical studies are necessary to determine whether the benefits of prophylaxis outweigh its risks and whether it is cost-effective. Until such data are available, risk for deep venous thrombosis must be assessed in all patients undergoing an orthopedic procedure. Thromboprophylaxis with pharmacologic agents may be considered in those at high risk.

According to a survey of practicing orthopedic surgeons, four of five surgeons provide a form of thromboembolic prophylaxis to all patients undergoing elective total hip arthroplasty (THA).¹ The rates for prophylactic use in elective total knee arthroplasty (TKA) were similar.¹ However, compared with joint replacements, more lower extremity orthopedic procedures (eg, knee arthroscopy) are performed in the United States each year. More than 95% of these procedures are for therapeutic indications. When compared with diagnostic interventions, therapeutic arthroscopy requires more operating time and creates more local trauma. Therefore, therapeutic arthroscopy is likely to increase the risk of deep venous thrombosis.² This risk may increase further as the rate of therapeutic arthroscopies rises. Participation of the aging population in sports is another factor that may further increase the risk for deep venous thrombosis.²

The incidence of deep venous thrombosis in patients who have undergone knee arthroscopy is reported to be as high as 17.9%.² The effects of deep venous thrombosis in orthopedic surgery patients include pain and swelling, as well as an increased risk of recurrent venous thromboembolism and postthrombotic syndrome, which may compromise long-term functional improvement despite a positive surgical outcome and the clinical absence of postoperative deep venous thrombosis.³ Finally, deep venous thrombosis must also be considered to be a possible precursor for a potentially fatal pulmonary embolism.⁴ An analytic model applied to >42,000 patients undergoing TKA determined that, in the absence of prophylaxis, the mortality rate associated with venous thromboembolism is 3%.⁵

Despite the risk for venous thromboembolism in patients undergoing lower extremity procedures, such as knee arthroscopy, lower extremity fracture, and arthroscopic-assisted surgery, data that define which prophylactic approach should be used are sparse. Because there are no results from large controlled trials, clinicians have no single set of practical guidelines for preventing deep venous thrombosis in this patient population and thus face a significant clinical gap. This article examines risk factors and specific prophylactic strategies for deep venous thrombosis and offers recommendations for prophylaxis in patients undergoing knee arthroscopy, treatment for lower extremity fracture, and arthroscopic-assisted surgery.

Risk Factors for Deep Venous Thrombosis

Orthopedic surgery increases the risk of deep venous thrombosis, as does total joint surgery or trauma. Without prophylactic anticoagulation, the incidence of deep venous thrombosis after hip or knee arthroplasty is 40%-70% (as determined by venography).⁶ The risk associated with a particular procedure is additive to that of other procedure-related factors (eg, immobilization or use of a tourniquet), as well as to other risk factors (Table 1).

Thrombophilia (ie, a tendency toward hypercoagulability) is another important risk factor for deep venous thrombosis after orthopedic procedures. It may be caused by a variety of conditions including deficiencies in protein C, protein S, tissue plasminogen activator, plasminogen, or antithrombin III. Other causes to consider are activated protein C resistance; antiphospholipid antibody syndrome; hyperhomocystinemia; plasminogen activator inhibition, and an increase in alpha-2 antiplasmin. However, it is not necessary to investigate the possibility of thrombophilia in all patients. A work-up is indicated only in patients who have experienced a single idiopathic episode of venous thrombembolism and who have at least one of the following criteria: a family history of venous thromboembolism, thrombosis at age <50 years, thrombosis at an unusual site (such as the mesenteric or cerebral vein), a massive venous thrombosis, or recurrent episodes of venous thrombembolism.

The Caprini Thrombosis Risk Factor Assessment for Surgical Patients provides each patient with a total risk factor score based on points assigned to a variety of risk factors within 24 hours of surgery.⁷My colleagues and I modified the system into a form that is inserted directly into patients’ charts (Figure 1). Before surgery, the physician or care provider checks off each applicable risk factor and then tabulates a total score. In this scoring system, each risk factor, with the exception of age >60 years, thrombophilia, and a history of venous thrombembolism, has a value of 1. The total score then classifies a patient into low-, moderate-, or high-risk groups, each with its corresponding prophylactic strategy (Table 2). Patients at moderate risk (ie, those with two to four risk factors) receive mechanical or pharmacologic prophylaxis, whereas those with more than four risk factors receive a combination of mechanical and pharmacologic modalities.

The modified system allows physicians to follow a rational strategy with accountability and systematic assessment. Use of this system should improve the diagnostic yield associated with expensive screening procedures, such as venous duplex scanning, and should enable physicians to provide prophylaxis for similar patients in a reproducible fashion.

Incidence of Deep Venous Thrombosis

Knee Arthroscopy

Using accurate objective diagnostic tests, researchers in at least six prospective studies (Table 3) have attempted to assess the rate of deep venous thrombosis in patients who have undergone knee arthroscopy.^2,6,8-11 The average rate of deep venous thrombosis in 992 patients in the six trials is 6.2%, ranging from 2.9% in one ultrasound study¹¹ to 17.9% of 184 patients in a Canadian study of interpretable unilateral contrast venograms at 1 week.²

Figure 1: Thrombosis risk factor assessment for surgical patients. Click on the chart above for large view. (Adobe PDF format) Download a free copy of Acrobat Reader here.

In the latter trial, Demers et al² studied a consecutive cohort of patients who did not receive thromboprophylaxis before or after the procedure. The overall rate of proximal thrombosis in this study was 4.9%. Of the patients with demonstrated deep venous thromboses, 39.4% were asymptomatic.² Clinical assessment did not accurately detect deep venous thrombosis in this population, and an extensive list of risk factors for thromboembolism, with the exception of tourniquet application for >60 minutes, was not predictive of deep venous thrombosis.²

In addition to the 8% rate of deep venous thrombosis detected by duplex ultrasonography and phlebography (Table 3), Schippinger et al¹⁰ also found that 9% of study patients had objective evidence of pulmonary embolism on follow-up ventilation/perfusion lung scans obtained at 5 weeks postsurgery. Because of the absence of symptoms, eight of nine patients with pulmonary embolism would not have been diagnosed without the scan. Similarly, 50% of the deep venous thromboses would not have been detected based on clinical criteria alone.¹⁰ These data led the investigators to recommend routine prophylaxis in patients undergoing arthroscopic knee surgery.¹⁰

In the study conducted by Schippinger et al,¹⁰ 12% of patients had a thromboembolic event despite perioperative anticoagulation with high-dose dalteparin (5000 IU subcutaneously each day). However, the low-molecular-weight heparin was stopped at discharge rather than continued for a longer period. Similarly, another study found that four out of five occurrences of symptomatic postoperative deep venous thromboses developed once thromboprophylaxis with nadroparin (2850 U subcutaneously each day) was stopped at day 5 or 6.¹²

These data confirm that deep venous thrombosis is a clinical challenge in patients undergoing TKA because of its asymptomatic nature and the associated risk, though low, of pulmonary embolism.

Lower Extremity Fractures

Although fractures of the lower extremity are common, the risk of venous thromboembolism in this patient population has been poorly studied. Key studies that have been conducted are discussed in Table 4.

Older data indicate that 17.1% of patients treated surgically for tibial fractures experience thrombosis, as well as 38.7% of patients with tibial fractures managed conservatively.¹³ The overall incidence of thrombosis in this study was 44.7%. Patients in the lowest age stratum (15-24 years) exhibited an 11.8% incidence of thrombosis in the absence of thromboprophylaxis.¹³

In a more recent venographic study of 102 patients undergoing early operative fixation of isolated lower extremity fractures distal to the hip, the overall rate of clinically occult deep venous thrombosis was 28%.¹⁴ The incidence of deep venous thrombosis by fracture site in this prospective study is shown in Table 5. Of 33 positive venograms, four demonstrated deep venous thrombosis in or proximal to the popliteal fossa.¹⁴The risk of chronic leg swelling after these types of fractures is unknown.

In this study, three factors significantly predicted occurrence of deep venous thrombosis: older age (>60 years), longer intervals until surgery (>27 hours), and longer surgical time (105 minutes). The researchers advocate prophylaxis with an anticoagulant or screening for deep venous thrombosis in patients with any of the following: femoral shaft or tibial plateau fractures, prolonged operations, high-energy injury, or lower-limb trauma in older persons.¹⁴

Wang et al¹⁵ described three case reports of pulmonary embolism after surgical repair of malleolar fractures and reviewed the medical literature for the reported prevalence of symptomatic venous thromboembolism after foot and ankle surgery. Although the incidence of deep venous thrombosis (0.22%) and nonfatal pulmonary embolism (0.15%) after foot and ankle surgery reported in one study was lower than that associated with hip or knee surgery, Wang et al¹⁵ found that the delayed occurrence of such events reported in that study (an average of 34.8 days after surgery) may contribute to underrecognition.¹⁶

In 1993, Spannagel and Kujath¹⁷ reported the results of a prospective trial that assessed the efficacy of self-injected low-molecular-weight heparin (nadroparin 2850 U per day subcutaneously) in preventing thromboembolism in 253 patients who required plaster casts due to injury of the lower limb. The overall rate of thrombosis in patients who did not receive thromboprophylaxis was 16.5%, and the rate in the subgroup of untreated patients with fractures was 29%. Prophylactic administration of the anticoagulant significantly lowered both of these rates. The overall rate of thrombosis in patients receiving low-molecular-weight heparins decreased to 4.8% and the rate in patients with fractures decreased to 10.3%.¹⁷ In a similar study, the rate of deep venous thrombosis in the control group was 4.3%; prophylactic administration of a low-molecular-weight heparin (certoparin, 3000 U per day subcutaneously) decreased the rate of deep venous thrombosis to 0, although results from this unblinded trial are limited by its design.¹⁸

Recently, Lassen et al¹⁹ reported the results of a prospective, randomized, double-blind trial of subcutaneous reviparin (1750 anti-Xa IU per day) versus placebo in patients undergoing plaster-cast immobilization for lower extremity fracture or rupture of the Achilles tendon. In the absence of thromboprophylaxis, 19% of patients demonstrated deep venous thrombosis by unilateral venography. The rate of deep venous thrombosis decreased to 9% in patients receiving a low-molecular-weight heparin.¹⁹

Recommendations for Prophylaxis

Knee Arthroscopy

Postoperative thromboprophylaxis is standard practice in patients undergoing hip procedures. However, it is relatively uncommon in patients undergoing TKA.

In the first randomized, controlled trial of thromboprophylaxis in this population, Wirth et al⁶ found that patients who received a 7- to 10-day course of a low-molecular-weight heparin (reviparin, 1750 IU per day subcutaneously) had an 80% relative risk reduction in developing venous thromboembolism than patients who received no active prophylaxis. The researchers concluded that because of the risk of deep venous thrombosis, routine prophylaxis should be administered to patients undergoing knee arthroscopic procedures.

In the absence of multiple prospective, controlled clinical trials of specific prophylactic interventions, how should physicians proceed clinically? It is appropriate to apprise all patients of the risk of deep venous thrombosis, especially when the procedure is for therapeutic purposes. Prophylaxis with a low-molecular-weight heparin or warfarin should be considered in patients with other risk factors who will be undergoing a procedure lasting >1 hour in which a tourniquet is used, such as collateral ligament reconstruction. If warfarin is used, it should be started 2-3 days before the procedure, so that the international normalized ratio is approximately 1.3 or 1.4 at the time of surgery. Depending on the patient’s other risk factors, postoperative prophylaxis for 7-10 days may be appropriate.

Lower Extremity Fracture

As reviewed earlier, prospective data from several clinical trials of various low-molecular-weight heparins indicate that prophylaxis may decrease the incidence of deep venous thrombosis in patients who are immobilized with plaster casts or braces for lower extremity fractures.¹⁹ For this population, I recommend to administer warfarin perioperatively, with the aim of maintaining a target international normalized ratio of 2.0-3.0 for 3-4 weeks. This regimen is followed with a 7- to 10-day postoperative course of either enoxaparin 40 mg subcutaneously once daily or dalteparin 5000 IU subcutaneously daily. Therapy may be continued when the patient has additional risk factors or a history of deep venous thrombosis or pulmonary embolism, or when the patient requires continued immobility.

Arthroscopic-Assisted Surgery

Patients who are undergoing medial or lateral meniscectomy or loose body surgery can be classified into type I or type II risk levels. The type I risk group involves patients who are 30-40 years old with no other risk factors. Generally, these patients can be managed with elastic graduated compression stockings, early ambulation, and probably no pharmacologic prophylaxis. Type II risk includes older patients who have multiple risk factors; these patients require more aggressive prophylaxis.

Patients undergoing arthroscopic-assisted repair of the anterior cruciate ligament (ACL) should be questioned to obtain a precise history of any previous deep venous thrombosis. Answers to the following questions should be solicited: Was the diagnosis made by venous Doppler, ultrasound, or venogram? Was a needle stick performed in the foot? Did the patient receive any dye? Which anticoagulants were administered?

A patient requiring arthroscopic-assisted repair of an ACL injury who has documentation of a previous deep venous thrombosis or pulmonary embolism by accurate diagnostic studies would be considered in the type II risk group. In such a patient, treatment with warfarin (5-7.5 mg) can be started the night before the procedure or enoxaparin (30 mg subcutaneously) every 12-24 hours after surgery. Home healthcare personnel and/or patients’ family members should be notified that the patient will be taking a low-molecular-weight heparin for 5 days in conjunction with warfarin and will require home or laboratory prothrombin/international normalized ratio tests. The low-molecular-weight heparin should be continued until the patient’s international normalized ratio is >1.8. Warfarin should be administered for 3-4 weeks, with the international normalized ratio between 2.0 and 3.0. Alternatively, the low-molecular-weight heparin can be continued for 3-4 weeks.

Conclusion

Multiple studies that systematically screen for venous thromboembolism with accurate tests such as venography and lung scans demonstrate that orthopedic procedures in the lower extremities are associated with a definite incidence of deep venous thrombosis and a risk of pulmonary embolism. These studies also underscore the prominence of clinically occult findings. Few prospective studies evaluating the efficacy and safety of thromboprophylaxis are available. However, limited data suggest that routine administration of a low-molecular-weight heparin reduces the rate of deep venous thrombosis in patients undergoing non–large-joint surgeries. In the absence of substantive clinical data for this indication, it is difficult to determine whether the benefits of prophylaxis outweigh any risks and whether it is a cost-effective strategy. The risk for deep venous thrombosis must be evaluated in all patients. Patients at high risk may benefit from prophylaxis.

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Authors

From the Baylor College of Medicine, Houston, Tex.