A rotatable arm is provided which provides an ability to rotate a working end of an instrument such as a surgical retractor. Rotation of a key hub transfers torque to a drive hub which causes an extension or retraction of a lead screw along a center axis of the rotating arm. The extension or retraction forces a drive pin to bear against sides of helical slots of a driven tip, producing a rotation of the driven tip along a pitch line of the helical slots. The driven tip is connected to the working end such that the two rotate together. The rotatable arm has a low profile, a non-reversible torque transmission, and may be hermetically sealed.