A surgical distraction device is provided for applying extending or tensioning force non-invasively to a patient's skeleton or to an implant which comprises anchoring means for attaching first and second components of the device to a bone or to adjoining bones, said components being connected by a linkage of an extendible length, a magnet connected to the linkage via a reduction gearbox and actuating means located externally of the patient for generating a moving or varying electromagnetic field, thereby causing the magnet to rotate and the linkage to be extended.
