An extension device, comprising a support surface for the patient and an extension bar (16), which can be attached at one of its ends by means of an interface (14) to the support surface for the patient and which has in its another end a retaining element (26) for a traction spindle arrangement (28), the support surface for the patient having at least two longitudinal bars (10) parallel to each other, which carry a support plate for the pelvis, characterized in that the interface (14) comprises a coupling part on the side of the support surface (36) and a coupling part on the side of the bar (38) rigidly attached to the extension bar (16), whereby the part of coupling on the side of the support surface (36) is housed in one of the longitudinal bars (10) rotatably about a perpendicular axis with respect to the support plate for the pelvis and by which the coupling part of the side of the A support surface (36) can be immobilized to prevent a rotation around its axis of rotation with respect to the extension bar (10) by means of an immobilization device (72, 74), which can be actuated by a remote drive device (94, 90).Un dispositivo de extensión, que comprende una superficie de soporte para el paciente y una barra de extensión (16), que puede unirse en uno de sus extremos mediante una interfaz (14) a la superficie de soporte para el paciente y que tiene en su otro extremo un elemento de retención (26) para una disposición de husillo de tracción (28), teniendo la superficie de soporte para el paciente al menos dos barras longitudinales (10) paralelas entre sí, que portan una placa de apoyo para la pelvis, caracterizado porque la interfaz (14) comprende una parte de acoplamiento del lado de la superficie de soporte (36) y una parte de acoplamiento del lado de la barra (38) rígidamente unida a la barra de extensión (16), por que la parte de acoplamiento del lado de la superficie de soporte (36) está alojada en una de las barras longitudinales (10) de forma giratoria alre
