IRCT20200118046174N2 IRCT 2021-01-09 Tehran University of Medical Sciences Comparison of aspirin for the prevention of venous thrombosis after knee and pelvic orthoplasty Comparison of low and high dose aspirin in prevention of venous thromboembolism after hip and knee arthroplasty 2020-05-21 anticipated 540 Complete https://irct.ir/trial/52520 interventional Randomization: Randomized, Blinding: Double blinded, Placebo: Not used, Assignment: Parallel, Purpose: Other, Other design features: comparison, Randomization description: In this study, the law of random allocation based on computer program randomization is used to randomize the treatment groups, so that 540 samples are randomly assigned to group A (aspirin 80) and B (aspirin 320) ( Random allocation table). In this way, patients attended to the hospital for surgery receive a single code and based on that code, one of the two treatment groups is considered for them. Also, in order to blind the study, envelopes containing cards with numbers 1 to 540 (number of study sample volumes) are prepared and the lids of the letter envelopes are glued and placed in a box. At the beginning of the registration, according to the order of entry of eligible participants to the study , one of the envelopes opened and its assigned group revealed based on the number registered on the participant card. It should be noted that these envelopes are only for one person and that number cant any longer be taken. Example: For the first patient, one of the envelopes in the box is selected. It is seen after opening box number 25. After referring to the random allocation table, it is observed that patient 25 should receive drug B, which is defined as aspirin 320. In order to ensure the status of the allocations and non-repetition, after selecting the groups and knowing the status of the treatment, the information will be inserted in a table (like the table below) , Blinding description: The study is double-blind ,means both surgeon (specialist assistant) and patient don't know the dose of prophylactic medicine .After surgery doctor will be informed .Hospitalization time, surgeon, pain control protocol ,anesthesia technique and volume of intraoperative lavage are similar in both groups and postoperative rehabilitation is the same . 3 deep vein thrombosis. Intervention 1: Intervention group: patients who underwent total knee or hip arthroplasty receive 80 mg aspirin twice a day for 4-6 weeks. Intervention 2: Intervention group2 : patients who underwent total knee or hip arthroplasty receive 325mg aspirin twice a day for 4-6 weeks. Undecided - It is not yet known if there will be a plan to make this available Justification or reason for indecision in sharing IPD is "There is no further information."