Dr. Betz's Therapiezentrum Martinsmühle site also provides good information about the procedure. See especially the "Implantation technique" link on the left side of the home page.

The Fitbone® device is being used by Prof. Augustin Betz in Germany and appears to be the only device that uses a powered system to lengthen the legs. The bones of the leg (Tibia and/or Femur) are cut and the intramedullary telescoping nail is implanted in the bone marrow of each bone. Each end of the telescope nail is attached to each end of the cut bone. The nail is connected to an induction receiver that is placed just under the skin. An external control unit powers the telescope nail though the induction plate. A similar technique has been used to power artificial hearts.Additional information is available from the The Fitbone® site.