A device (1) for patient body positioning and immobilizing has four pressing pieces (41-44) for immobilizing the lumbar region of a patient (P) in lateral decubitus position on a table (B). The first pressing piece (41) and the second pressing piece (42) are arranged in a position corresponding to the anterior superior iliac spine (AS) of the patient (P). The third pressing piece (43) is arranged in a position corresponding to the pubic symphysis (PS) of the patient (P). The fourth pressing piece (44) pushes against the back surface of the lumbar region of the patient (P). The plane (P2) containing each of the pressing planes (F1-F3) of the first, second and third pressing pieces (41-43) is parallel to the patient (P)'s pelvic floor reference plane (P1). An angle indicator (6) is attached to a stand (30) supporting the first, second and third pressing pieces (41-43). The angle indicator (6) has an indicating rod (63). A first angle (θ1) and a second angle (θ2) specifying the orientation of the indicating rod (63) with respect to the pelvic floor reference plane (P1) can be each regulated with a first angle regulator (61) and a second angle regulator (62). During a hip replacement arthroplasty, a rod (R) of a surgical instrument (OT) is held parallel with the indicating rod (63), and a cup (CP) is inserted in the patient (P)'s acetabulum using the surgical instrument (OT).Selon l'invention, un dispositif (1) de maintien de posture comprend 4 pièces (41-44) de poussée pour maintenir la région lombaire d'un patient (P) en position latérale sur une table (B). La première (41) et la deuxième (42) pièces de poussée sont placées dans une position correspondant à l'épine iliaque antéro-supérieure (AS) du patient (P). La troisième pièce (43) de poussée est placée dans une position correspondant à la symphyse pubienne (PS). La quatrième pièce (44) de poussée appuie sur l'arrière de la région lombaire. Le plan (P2) contenant chacune des faces (F1-F3) de poussée des première, d
