<qa>  What is the most common orthopaedic procedure in the world?Total knee replacement TKR surgery is one the most common orthopaedic procedure in the world. Morbility in perioperative TKR is associated to: blood loss, pain, infection, wound complications, stiffness and thrombotic events. Blood loss and transfusion have been associated to increased hospital stay, costs, morbility and mortality of the patient. Indications for blood transfusions are now limited and it is well known that is not a free risk procedure. Complications such as; ABO incompatibility, viral transmission, hemolysis, immunosuppression and wound infection have been reported. 