The Phenix expandable prosthesis: early American experience.

One of the major dilemmas in limb preservation in skeletally immature children involves the ability to maintain leg length equality. Many attempts have been made to design a prosthesis that could be expanded easily either nonoperatively or through a minor surgical procedure. Most of these designs have had mechanical difficulty or the lengthening procedure becomes a major surgical endeavor. The Phenix technology has been used in France for several years. The basic principle involves storage of energy in a spring which is maintained compressed by an original locking system. Once implanted, prosthetic lengthening is achieved via exposure to an external electromagnetic field that pilots the locking system and allows controlled release of the spring energy. Seven Phenix prostheses have been implanted in six patients. All patients had been treated for Stage II-B osteosarcoma. Six of the seven prostheses were implanted during revision procedures in salvage situations; one prosthesis was implanted during an index procedure. The surgical procedures were completed without complications. One patient sustained a fracture of the prosthesis in a fall and had an infection develop after implantation of the second prosthesis. Twenty-one expansions have been performed in six patients (mean lengthening at each procedure, 8 mm). There were no acute complications attributable to the lengthening procedure. Prosthetic expansions required an average of 20 to 30 seconds and were accompanied by very mild discomfort, if any. Most patients were given an oral analgesic either before or during the lengthening procedure. The Phenix prosthesis shows promise in handling the difficult problem of limb preservation in a growing child. Additional investigation is underway regarding limb lengthening and other dynamic applications.