Anti–PF4/heparin antibody formation in patients receiving fondaparinux or enoxaparin after orthopedic surgery (current status analysis). Data are combined for patients undergoing knee and hip replacement. (A) Anti–PF4/heparin antibodies of IgG class. There is no significant difference between the groups (P = .86). (B) All anti–PF4/heparin antibodies. There is no significant difference between the study drug groups (P = .24).