Clinical Pearls & Morning Reports
Published February 8, 2017
Patients who undergo arthroscopic knee surgery and patients who are treated with casting of the lower leg are at increased risk for venous thromboembolism (i.e., deep-vein thrombosis or pulmonary embolism). The Prevention of Thrombosis after Knee Arthroscopy (POT-KAST) and the Prevention of Thrombosis after Lower Leg Plaster Cast (POT-CAST) trials compared the incidence of symptomatic venous thromboembolism after these procedures between patients 18 years of age or older who received anticoagulant therapy (low-molecular-weight heparin) and those who received no anticoagulant therapy. (Read the Original Article.)
Q: What is known about the role of thromboprophylaxis for patients undergoing knee arthroscopy or lower-leg casting?
A: The use of pharmacologic thromboprophylaxis after most orthopedic interventions is well established, because it strongly reduces the risk of thrombosis while only slightly increasing the risk of bleeding. However, whether such prophylaxis is effective after arthroscopic knee surgery is uncertain, despite the fact that this procedure is the most commonly performed orthopedic procedure worldwide (performed in more than 4 million patients per year). It is also uncertain whether such prophylaxis is effective after casting of the lower leg, a treatment for which the risk for venous thromboembolism has not been reliably estimated.
Q: Is there evidence that routine thromboprophylaxis is effective for patients who undergo knee arthroscopy or lower-leg casting?
A: In the POT-KAST trial, low-molecular-weight heparin was administered once daily for the 8 days after arthroscopy; the first dose was administered postoperatively but before discharge on the day of surgery. In the POT-CAST trial, low-molecular weight heparin was administered for the full period of immobilization; the first dose was administered in the emergency department. In the two parallel trials, the authors found that treatment with anticoagulants, either for the 8 days after arthroscopy or during the complete period of immobilization due to casting, was not effective for the prevention of symptomatic venous thromboembolism.
A: In the POT-KAST trial, two patients had major bleeding: 1 patient (0.1%) in the treatment group had hemarthrosis of the knee, and 1 patient (0.1%) in the control group had bleeding at the surgical site 2 days after the procedure and underwent reoperation. In the POT-CAST trial, one clinically relevant nonmajor bleeding event occurred in 1 patient (0.1%) in the treatment group and in no patients in the control group, and no major bleeding events occurred.
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A: POT-KAST had limited power because the incidence of symptomatic venous thromboembolism was lower than expected (i.e., 0.6%). This incidence is in line with two recent observational studies that reported incidences of symptomatic venous thromboembolism of 0.3% (95% CI, 0.3 to 0.5) within 3 months after the procedure and 0.4% (95% CI, 0.2 to 0.5) within 6 weeks after the procedure, and in both studies, the vast majority of patients did not receive any anticoagulants. Furthermore, a meta-analysis showed a pooled incidence of symptomatic venous thromboembolism of 0.6% (95% CI, 0.3 to 1.1) in 571,793 arthroscopic meniscectomy procedures. In contrast, randomized trials have shown much higher incidences, ranging from 0.9% (95% CI, 0.3 to 2.1) to 5.3% (95% CI, 2.4 to 11.0), and sample sizes for POT-KAST and POT-CAST were calculated on the basis of these data.