Early multicenter experience with a noninvasive expandable prosthesis.

A noninvasive expandable prosthesis for skeletally immature children after limb salvage surgery has been developed. Between 1998 and 2001, 18 Phenix prostheses were implanted in 15 pediatric patients who had been diagnosed and treated for osteosarcoma about the knee. Of the 15 original prostheses, 10 were implanted at the time of primary tumor resection and five were revisions from an endoprosthetic modular knee system. Sixty expansions of the 18 prostheses were done, with all but two done as outpatient procedures. An average 8.5 mm was obtained per lengthening (range, 1-30 mm). The average followup was 21.5 months (range, 12-33 months) and the latest Musculoskeletal Tumor Society functional scores averaged 90%. Eight revisions were required for stem fracture or loosening. There was one amputation because of a postoperative arterial thrombosis. The principle of the Phenix prosthesis involves storage of energy in a spring compressed by a locking system. Lengthening is achieved via exposure to an electromagnetic field that allows controlled release of the spring. This is a unique expandable custom prosthesis that offers many benefits in maintaining limb length equality in growing patients. Although the early experience is promising, additional data are required regarding the long-term structural integrity of the prosthesis. We are optimistic that this technology will prove beneficial, not only for patients with malignant bone tumors but in applications requiring serial limb length equalizations or for spinal deformities.