In an extension device comprising a patient support surface and an extension beam (16) that can be connected on its one end via an interface (14) to the patient support surface and that has a holder for a feed rod arrangement on its other end, whereby the patient support surface has at least two longitudinal beams (10) parallel to each other that carry a pelvic support plate, the interface (14) comprises a coupling part (36) on the support surface side and comprises a coupling part (38) on the beam side and rigidly connected to the extension beam (16), whereby the coupling part (36) on the support surface side on one of the longitudinal beams (10) is supported in such a manner that it can pivot about an axis perpendicular to the pelvic support plate, and whereby the coupling part (36) on the support surface side can be locked by a locking device against a rotation about its pivot axis relative to the longitudinal beam (10), which locking device can be actuated by a remote actuation.
