A driver assembly detachably coupled between a flexible shaft drive transmission having an outer casing and an elongated drive transmitting shaft rotatable within the outer casing and a handle assembly of a power operated toot to provide rotational power from a coupler fitting of the drive transmitting shaft and a drive train of the power operated rotary knife. The driver assembly includes: a tube assembly comprising a main tube defining a throughbore and first and second bushings disposed within the throughbore at respective first and second ends of the main tube and a casing coupler secured to and extending beyond the second end of the main tube, the casing coupler configured to releasably attach the driver assembly to the outer casing; and an elongated shaft supported for rotation by the first and second bushings of the tube assembly.