Epidemiology

In the United States, more than 540,000 total knee replacements and more than 230,000 total hip replacements are performed annually. In addition to patients undergoing hip fracture repair surgery, patients undergoing these major orthopedic surgeries are one of the highest risk groups for developing postoperative VTE, which comprises deep vein thrombosis (DVT) and pulmonary embolism (PE). Large randomized clinical trials have shown that patients’ risk for developing proximal DVT, the thrombi that are most likely to cause PE, is 10% to 30%. Symptomatic VTE occurs in 1.3% to 10% of patients within 3 months of surgery, and after total hip replacement, 1 patient in 300 will die from PE if VTE prophylaxis is not used. Patients undergoing other types of orthopedic surgery are also at increased risk for VTE, and proximal DVT in these patients can also lead to life-threatening PE. VTE is also a common cause of readmission to the hospital. Moreover, hospital costs and hospital stay are doubled for patients who develop VTE after surgery. VTE is also associated with potentially serious long-term complications, including post-thrombotic syndrome, cardiorespiratory insufficiency, recurrent VTE, and bleeding associated with the use of treatment doses of anticoagulants.

Pathophysiology

Many factors contribute to the development of VTE after major orthopedic surgery (Table 59-1). Trauma and surgery both contribute to venous injury and activation of the coagulation system. Postoperatively, patients may have impaired mobility, which causes stasis of blood flow in the deep venous system. Patients undergoing certain types of orthopedic surgery, such as joint replacement and hip fracture repair surgery, also tend to be older and typically have medical comorbid conditions. Increased age is recognized as an independent risk factor for VTE as well.

Most episodes of postoperative DVT are clinically silent, since they develop when patients are recumbent or have limited mobility. (Typically, clinical features of vein obstruction in ambulatory patients cause lower limb swelling and pain.) Although a considerable proportion of such thrombi will resolve spontaneously without administration of antithrombotic therapy, 25% to 50% of clots grow and cause symptomatic DVT or PE.

Does This Patient Undergoing Hip Fracture Repair, Hip Replacement, or Knee Replacement Need VTE Prophylaxis?

Patients undergoing hip fracture repair, hip replacement, or knee replacement are considered to be at the highest risk for VTE among all orthopedic surgery patients. Prophylaxis is safe and effective in these patients. For this reason, VTE prophylaxis is routinely recommended.

Does This Patient Undergoing Elective Spine Surgery Need VTE Prophylaxis?

Though patients undergoing elective spine surgery are at lower risk of VTE than those undergoing hip fracture surgery or lower-extremity joint replacement, they should be considered for VTE prophylaxis. Patients undergoing these surgeries tend to be less mobile in the postoperative period, and the surgeries themselves tend to be longer. They may have additional risk factors, such as advanced age, malignancy, presence of a neurologic deficit, previous VTE, or an anterior surgical approach. If a patient has none of these risk factors and can ambulate early and frequently, no additional thromboprophylaxis needs to be considered. However, if there are additional risk factors present, thromboprophylaxis should be used. There are no large randomized trials in this area, but the data suggest that postoperative low-dose unfractionated heparin (LDUH) and postoperative low molecular weight heparin (LMWH) are beneficial. If intermittent pneumatic compression devices (IPC) are used (for example, in patients at increased bleeding risk), they should be put on in the operating room, and continued postoperatively.

Does This Patient Undergoing a Minor Orthopedic Procedure Need VTE Prophylaxis?

Knee arthroscopy, either to examine the knee or to perform minimally invasive surgery, is a very common orthopedic procedure. More than 5 million arthroscopies are performed in the United States every year. However, the risk of symptomatic VTE appears to be very low, at less than 1%. A systematic review concluded that the benefit of using LMWH compared with no prophylaxis in knee arthroscopy patients was similar to the harm. (Number need to treat = 20, number needed to harm = 17.) A recent randomized controlled trial that compared full-length graduated compression stockings to prophylactic LMWH showed that prophylactic LMWH for 1 week reduced a composite end point of asymptomatic proximal deep venous thrombosis, symptomatic venous thromboembolism, and all-cause mortality. However, nearly half of the events making up the composite outcome measure were distal vein thrombi, which have questionable clinical significance. At this time, routine thromboprophylaxis is not recommended after knee arthroscopy, unless the patient has other risk factors for clotting or has a complicated procedure that results in prolonged immobility.

Isolated distal leg injuries (occurring below the knee) that require orthopedic stabilization with a cast or splint but no surgical intervention are also very common problems in the orthopedic surgery setting. There have been a number of randomized clinical trials of prophylaxis in patients with these injuries. LMWH was not clearly shown to reduce the frequency of DVT compared with no prophylaxis. Practice patterns vary, but the most recent American College of Chest Physicians (ACCP) guidelines recommend that patients with isolated distal leg injuries do not receive routine thromboprophylaxis.

Physicians have a number of options available when choosing the type of VTE prophylaxis. In patients with an increased risk for bleeding (Table 59-2

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