THROMBOPROPHYLAXIS AFTER TOTAL KNEE ARTHROPLASTY

Abstract

Total knee replacement surgery became one of the most common and successful surgeries in the last decades. Patients undergoing total knee replacement surgery are at high risk for developing venous thromboembolic events such as deep venous thrombosis and pulmonary embolism which may be a fatal condition. Therefore, different methods of thromboprophylaxis are essential after total knee replacement surgery. Detailed anatomy of the venous system of the lower limb was discussed in this essay. The role of venous valves and the calf muscle pump was shown in returning the blood back to the circulation avoiding its stagnation in the veins of the leg. In this essay we explained multiple risk factors that increase the incidence of deep venous thrombosis. Previous attacks of venous thromboembolism and family history are main risk factors for DVT. Patients with malignancies and others having chronic diseases such as congestive heart failure and respiratory failure have more chances for developing DVT. Other risk factors include obesity, old age, varicose veins and immobility. Also hypercoagulable conditions due to elevated coagulation factors or patients on oral contraceptive recommend thromboprphylaxis. Several mechanical methods are used in reducing the incidence of DVT. Although these methods are ineffective alone in moderate or high risk cases, yet their usage is advised in patients having high bleeding risk to avoid complications of anticoagulants. Modalities include graduated compression stockings, venous foot pumps and intermittent pneumatic devices. Mechanical methods have been shown to be useful adjunct to anticoagulation therapy. These methods act by increasing blood flow of venous return in leg veins. But generally, mechanical methods are not well tolerated by the patients as they do not have established standards for size, pressure, and duration. They always need continues effort to ensure their proper use. Also, postoperative autologous blood transfusion showed to reduce the incidence of thromboembolism after TKA. Various pharmacological agents werediscussedwith stress on new oral anticoagulants. Although aspirin and warfarin have the advantages of ease of use and low cost, but it is clearly not the best evidence-based approach for DVT prophylaxis. Aspirin showed to have high rate of wound and gastrointestinal bleeding, while Warfarin requires continuous laboratory monitoring to adjust its dose. LMWHs are commonly used nowadays in prophylaxis of DVT after major orthopedic operations. They have the advantages of predictable dose response and less bleeding incidence. In comparison with other prophylactic methods such as warfarin and UFH, LMWHs have demonstrated improvement in DVT prophylaxis without increase in hemorrhagic complications. Fondaparinux was proven to be more effective than enoxaparin in preventing VTE after elective major knee surgery. Studies showed that the superiority of fondaparinux was related to its initiate selective inhibition of factor Xa, its predictable pharmacokinetics, the choice of dose and the starting time after surgery. New oral anticoagulant agents are more convenient than parenteral agents. They have predictable pharmacokinetic and pharmacodynamic properties, which means thatthey may be administered at a fixed dose without the need for coagulation monitoring. Recent studies showed that dabigatran (150 mg or 220 mg once/day) is a well-tolerated alternative to enoxaparin for the prevention of VTE after total knee replacement without increasing the incidence of bleeding. Rivaroxaban is a factor Xa inhibitor that is approved to be used in thromboprophylaxis after joint replacement surgery. Trials revealed that rivaroxaban was more effective than enoxaparin in preventing venous thrombosis, with similar rates of bleeding. Also apixaban, another factor Xa inhibitor, was compared with LMWH in prophylaxis of DVT. Trials showed that Apixaban did not decrease the incidence of thrombosis but was associated with lower rates of bleeding. Generally, anticoagulants must be taken for 10 to 14 days after the surgery and the doses of anticoagulants must be adjusted in patients with chronic renal insufficien