***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
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    ***EXAMPLES*** 
    Input: INTRODUCTION Perioperative blood loss is a frequent cause of complications in total hip replacement ( THR ) . The present prospect i ve study assessed the efficacy of tranexamic acid ( Exacyl ( ® ) ) in reducing blood loss in primary THR associated to rivaroxaban ( Xarelto ( ® ) ) thromboprophylaxis . HYPOTHESIS Tranexamic acid associated to rivaroxaban reduces blood loss . MATERIAL AND METHOD A prospect i ve case-control study included 70 primary cementless THRs performed by a single surgeon on a st and ardized technique , between September 2009 and September 2010 . Thirty-seven patients received perioperative tranexamic acid ;  all patients received rivaroxaban thromboprophylaxis . RESULTS There was no significant difference between the two groups in terms of peroperative blood-loss volume or rates of thromboembolic or ischemic events or hematoma . Postoperative blood loss , D0 - 5 differential hemoglobinemia and real blood loss ( in mL 100 % hematocrit ) were significantly lower in the tranexamic acid group . No transfusions were required in the tranexamic acid group , versus four in the control group . DISCUSSION Tranexamic acid associated to direct anti-Xa ( antithrombin-independent ) oral anticoagulants was effective in reducing postoperative blood loss , improving hemoglobinemia at 5 days and reducing transfusion rates . The results also confirmed the efficacy of and tolerance for rivaroxaban thromboprophylaxis in primary THR , with no clinical thrombotic events induced by the association of tranexamic acid with rivaroxaban . CONCLUSIONS Tranexamic acid is a simple means of reducing postoperative blood loss in THR , without increased risk of thromboembolism when associated to rivaroxaban thromboprophylaxis . LEVEL OF EVIDENCE Level III prospect i ve case-control study OBJECTIVE Prevention of deep venous thrombosis ( DVT ) and associated pulmonary embolism following major orthopedic surgeries is challenging , and there is an increased interest in developing new treatment strategies . We compared 2 switch-therapy modalities-enoxaparin to rivaroxaban and enoxaparin to dabigatran- and enoxaparin monotherapy for preventing DVT after total knee arthroplasty ( TKA ) and total hip arthroplasty ( THA ) . METHODS This was a prospect i ve , non-blinded , r and omized controlled study . We selected 180 eligible patients out of 247 patients undergoing TKA or THA . During the preoperative checkup , patients were r and omized to receive either enoxaparin ( enoxaparin group ) or switch-therapy regimens , comprising enoxaparin during hospitalization and rivaroxaban ( rivaroxaban group ) or dabigatran ( dabigatran group ) during the outpatient period . All patients were evaluated for DVT using Doppler ultrasonography ( USG ) 6 weeks postoperatively . The primary efficacy outcome was the prevention of symptomatic or Doppler ultrasonography (USG)-proven DVT , whereas the primary safety outcome was the incidence of bleeding during the DVT-prophylaxis period . RESULTS Doppler USG at 6 weeks after surgery revealed no signs of DVT in any patient . During the hospitalization period , only 2 major bleeding events were reported ( 1 [ 1.6 % ] in the enoxaparin group and 1 [ 1.6 % ] in the dabigatran group ) . No major bleeding events were reported during the outpatient follow-up period in any group . Differences among the 3 groups regarding bleeding events were not statistically significant ( p>0.05 ) . CONCLUSION When using switch-therapy modalities , clinicians can take advantage of the safety of enoxaparin during the hospitalization period and ease of use of new oral anticoagulant drugs during the outpatient period Objective To examine the duration and magnitude of increased risk of venous thromboembolism  after different types of surgery . Design Prospect i ve cohort study ( Million Women Study ) . Setting Question naire data from the Million Women Study linked with hospital admission and death records . Participants 947 454 middle aged women in the United Kingdom recruited in 1996 - 2001 and followed by record linkage to routinely collected NHS data on hospital admissions and deaths . During follow-up 239 614 admissions were for surgery ; 5419 women were admitted , and a further 270 died , from venous thromboembolism . Main outcome measures Adjusted relative risks and st and ardised incidence rates for hospital admission or death from venous thromboembolism ( pulmonary embolism or deep vein thrombosis ) , by time since and type of surgery . Results Compared with not having surgery , women were 70 times more likely to be admitted with venous thromboembolism in the first six weeks after an inpatient operation ( relative risk 69.1 , 95 % confidence interval 63.1 to 75.6 ) and 10 times more likely after a day case operation ( 9.6 , 8.0 to 11.5 ) . The risks were lower but still substantially increased 7 - 12 weeks after surgery ( 19.6 , 16.6 to 23.1 and 5.5 , 4.3 to 7.0 , respectively ) . This pattern of risk was similar for pulmonary embolism ( n=2487 ) and deep venous thrombosis ( n=3529 ) . The postoperative risks of venous thromboembolism varied considerably by surgery type , with highest relative risks after inpatient surgery for hip or knee replacement and for cancer—1 - 6 weeks after surgery the relative risks were , respectively , 220.6 ( 187.8 to 259.2 ) and 91.6 ( 73.9 to 113.4 ) . Conclusion The risk of deep vein thrombosis and pulmonary embolism after surgery is substantially increased in the first 12 postoperative weeks , and varies considerably by type of surgery . An estimated 1 in 140 middle aged women undergoing inpatient surgery in the UK will be admitted with venous thromboembolism during the 12 weeks after surgery ( 1 in 45 after hip or knee replacement and 1 in 85 after surgery for cancer ) , compared with 1 in 815 after day case surgery and only 1 in 6200 women during a 12 week period without surgery BACKGROUND This phase 3 trial compared the efficacy and safety of rivaroxaban , an oral direct inhibitor of factor Xa , with those of enoxaparin for extended thromboprophylaxis in patients undergoing total hip arthroplasty . METHODS In this r and omized , double-blind study , we assigned 4541 patients to receive either 10 mg of oral rivaroxaban once daily , beginning after surgery , or 40 mg of enoxaparin subcutaneously once daily , beginning the evening before surgery , plus a placebo tablet or injection . The primary efficacy outcome was the composite of deep-vein thrombosis ( either symptomatic or detected by bilateral venography if the patient was asymptomatic ) , nonfatal pulmonary embolism , or death from any cause at 36 days ( range , 30 to 42 ) . The main secondary efficacy outcome was major venous thromboembolism ( proximal deep-vein thrombosis , nonfatal pulmonary embolism , or death from venous thromboembolism ) . The primary safety outcome was major bleeding . RESULTS A total of 3153 patients were included in the superiority analysis ( after 1388 exclusions ) , and 4433 were included in the safety analysis ( after 108 exclusions ) . The primary efficacy outcome occurred in 18 of 1595 patients ( 1.1 % ) in the rivaroxaban group and in 58 of 1558 patients ( 3.7 % ) in the enoxaparin group ( absolute risk reduction , 2.6 % ; 95 % confidence interval [ CI ] , 1.5 to 3.7 ; P<0.001 ) . Major venous thromboembolism occurred in 4 of 1686 patients ( 0.2 % ) in the rivaroxaban group and in 33 of 1678 patients ( 2.0 % ) in the enoxaparin group ( absolute risk reduction , 1.7 % ; 95 % CI , 1.0 to 2.5 ; P<0.001 ) . Major bleeding occurred in 6 of 2209 patients ( 0.3 % ) in the rivaroxaban group and in 2 of 2224 patients ( 0.1 % ) in the enoxaparin group ( P=0.18 ) . CONCLUSIONS A once-daily , 10-mg oral dose of rivaroxaban was significantly more effective for extended thromboprophylaxis than a once-daily , 40-mg subcutaneous dose of enoxaparin in patients undergoing elective total hip arthroplasty . The two drugs had similar safety profiles . ( Clinical Trials.gov number , NCT00329628 . BACKGROUND The role of aspirin in thromboprophylaxis after total hip arthroplasty ( THA ) is controversial . OBJECTIVE To compare extended prophylaxis with aspirin and dalteparin for prevention of symptomatic venous thromboembolism ( VTE )  after THA . DESIGN Multicenter r and omized , controlled trial with a noninferiority design based on a minimal clinical ly important difference of 2.0 % . R and omization was electronically generated ; patients were assigned to a treatment group through a Web-based program . Patients , physicians , study coordinators , health care team members , outcome adjudicators , and data analysts were blinded to interventions . ( Current Controlled Trials : IS RCT N11902170 ) . SETTING 12 tertiary care orthopedic referral centers in Canada . PATIENTS 778 patients who had elective unilateral THA between 2007 and 2010 . INTERVENTION After an initial 10 days of dalteparin prophylaxis after elective THA , patients were r and omly assigned to 28 days of dalteparin ( n = 400 ) or aspirin ( n = 386 ) . MEASUREMENTS Symptomatic VTE confirmed by objective testing ( primary efficacy outcome ) and bleeding . RESULTS Five of 398 patients ( 1.3 % ) r and omly assigned to dalteparin and 1 of 380 ( 0.3 % ) r and omly assigned to aspirin  had VTE ( absolute difference , 1.0 percentage point [ 95 % CI , -0.5 to 2.5 percentage points ] ) . Aspirin was noninferior ( P < 0.001 ) but not superior ( P = 0.22 ) to dalteparin . Clinical ly significant bleeding occurred in 5 patients ( 1.3 % ) receiving dalteparin and 2 ( 0.5 % ) receiving aspirin . The absolute between-group difference in a composite of all VTE and clinical ly significant bleeding events was 1.7 percentage points ( CI , -0.3 to 3.8 percentage points ; P = 0.091 ) in favor of aspirin . LIMITATION The study was halted prematurely because of difficulty with patient recruitment . CONCLUSION Extended prophylaxis for 28 days with aspirin was noninferior to and as safe as dalteparin for the prevention of VTE after THA in patients who initially received dalteparin for 10 days . Given its low cost and greater convenience , aspirin may be considered a reasonable alternative for extended thromboprophylaxis after THA . PRIMARY FUNDING SOURCE Canadian Institutes of Health Research Rivaroxaban demonstrated superior efficacy and a similar safety profile to enoxaparin for the prevention of venous thromboembolism in the phase III RECORD programme in patients undergoing elective hip or knee replacement surgery . The XAMOS study investigated adverse events , including bleeding and thromboembolic events , in patients receiving rivaroxaban for thromboprophylaxis in routine clinical practice . XAMOS was a non-interventional , open-label cohort study in patients undergoing major orthopaedic surgery of the hip or knee ( predominantly elective arthroplasty ) , in which rivaroxaban was compared with other pharmacological thromboprophylaxis . All adverse events were documented , including symptomatic thromboembolic and bleeding events . Crude and adjusted incidences based on propensity score subclasses were calculated and compared between the rivaroxaban and st and ard-of-care groups . A total of 17,701 patients were enrolled from 252 centres in 37 countries .  Crude incidences of symptomatic thromboembolic events three months after surgery in the safety population were 0.89 % in the rivaroxaban group ( n=8,778 ) and 1.35 % in the st and ard-of-care group ( n=8,635 ; odds ratio [ OR ] 0.65 ; 95 % confidence interval [ CI ] 0.49 - 0.87 ) , and 0.91 % and 1.31 % ( weighted ) in the propensity score-adjusted analysis ( OR 0.69 ; 95 % CI 0.56 - 0.85 ) , respectively . Treatment-emergent major bleeding events ( as defined in the RECORD studies ) occurred in 0.40 % and 0.34 % 
    Output:
    
The results of the studies showed some cases of pulmonary embolism , deep vein thrombosis , and bleeding ; even then , the NOACs were effective in preventing thromboembolic events .
There is no consensus regarding the prophylaxis method for these events , which is why the challenge is to obtain high levels of prevention while minimizing the adverse effects .