The relative risk of infection from transfusions after arthroplasty: Commentary on articles by Richard Friedman, MD, FRCSC, et al.: "Allogeneic blood transfusions and postoperative infections after total hip or knee arthroplasty" and Erik T. Newman, MD, et al.: "Impact of perioperative allogeneic and autologous blood transfusion on acute wound infection following total knee and total hip arthroplasty".