Low molecular weight heparin (LMWH) at preventive doses after arthroscopic knee surgery or leg casting did not prevent venous thromboembolism (DVT or PE), in two Dutch randomized trials. The study helps fill a large gap in knowledge regarding risks and benefits of prophylactic anticoagulation in patients undergoing these procedures.
In one (POT-KAST), 1,543 patients received either nadroparin (Fraxiparine) or dalteparin (Fragmin) — both LMWH — once daily for 8 days after knee surgery or no anticoagulant (non-blinded, no placebo). Symptomatic venous thromboembolism (DVT or PE) occurred in 0.7% of the heparin group, and 0.4% rate among the controls. Major bleeding occurred in 0.1% of each group, with no deaths in 3 months of follow-up.
In POT-CAST, the same investigators used the same LMWH products among 1,519 patients who were immobile due to lower leg casting. Patients were randomized to either prophylactic anticoagulation or none: 1.4% of patients receiving LMWH, and 1.8% of controls experienced DVT or PE, with no major bleeding.
[R]outine thromboprophylaxis with the standard regimen is not effective after knee arthroscopy or lower-leg casting … In light of the high frequency of knee arthroscopy and casting worldwide, a considerable number of cases of venous thromboembolism will nevertheless occur, and any possible prevention of these events should still be pursued.
They argue against higher doses or longer duration of treatment for most patients, believing that bleeding risks would outweigh any benefits.
In the U.S., enoxaparin (Lovenox) is typically used rather than dalteparin. Nadroparin is not available in the U.S. There was only a 0.6% incidence of symptomatic DVT or PE in POT-KAST, lower than expected, making any benefit of prophylaxis almost impossible to detect.
The study provides convincing evidence against a practice of routine anticoagulation prophylaxis for patients undergoing the relatively less invasive arthroscopic knee surgeries or leg casting.
The study supports the 2012 guidelines from the American College of Chest Physicians, which state,
For patients with isolated lower-extremity injuries requiring leg immobilization, we suggest no thromboprophylaxis (Grade 2B). For patients undergoing knee arthroscopy without a history of VTE, we suggest no thromboprophylaxis (Grade 2B).
The American Academy of Orthopedic Surgeons (AAOS) has not previously published its recommendations for anticoagulation prophylaxis for leg casting or arthroscopy.
High-risk patients might still benefit from anticoagulation prophylaxis associated with these lower-risk procedures, and should be considered on a case by case basis.