Embodiments of the invention include implantable apparatus including a magnet and related methods that can be used to lengthen the limbs of a subject. In an embodiment, the invention includes a limb lengthening apparatus including a magnet and a piston having a lengthwise axis, the magnet oriented so as to cause movement of the piston along its lengthwise axis in response to application of an external magnetic field. The apparatus also includes a first body member and a second body member, the first body member and second body member configured to be disposed lengthwise within the bone of a limb to be lengthened. The apparatus also includes a lengthening mechanism, the mechanism including a drive nut, wherein sequential application and removal of the external magnetic field causes the drive nut to rotate around the lengthwise axis of the piston causing the distance between the first body member and the second body member to increase. Other embodiments are also included herein.
