Abstract: A therapeutic hospital bed (1) comprises a patient support platform (2) rotatably and pivotally secured within a main bed frame (3). The main bed frame (3) is supported on a base frame (5). An end board on the patient support platform (2) has an arcuate track (14) engaged by a drive belt (15) which is connected to a drive motor for oscillating the patient support platform (2) relative to the main bed frame (3). Opposite ends of the drive belt (15) are connected to disengagement arms (18, 25) which are pivotally interconnected to form a scissors mechanism. The arms (18, 25) are operable to tension or release the belt (15) to engage or disengage drive to the patient support platform (2). A spring (27) extends between the arms (18, 25) to bias the arms (18, 25) into a belt tensioning position. To disengage the drive for turning the patient support platform (2) manually, the arms (18, 25) are movable against spring bias to a disengaged position.