The Phenix expandable prosthesis - Early American experience

One of the major dilemmas in limb preservation in skeletally immature child ren involves the ability to maintain leg length equality. Many attempts hav e been made to design a prosthesis that could be expanded easily either non operatively or through a minor surgical procedure. Most of these designs ha ve had mechanical difficulty or the lengthening procedure becomes a major s urgical 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, prost hetic lengthening is achieved via exposure to an external electromagnetic f ield that pilots the locking system and allows controlled release of the sp ring energy. Seven Phenix prostheses have been implanted in six patients. A ll 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 proce dures were completed without complications. One patient sustained a fractur e of the prosthesis in a fall and had an infection develop after implantati on of the second prosthesis. Twenty-one expansions have been performed in s ix patients (mean lengthening at each procedure, 8 mm). There were no acute complications attributable to the lengthening procedure. Prosthetic expans ions required an average of 20 to 30 seconds and were accompanied by very m ild discomfort, if any. Most patients were given an oral analgesic either b efore or during the lengthening procedure. The Phenix prosthesis shows prom ise in handling the difficult problem of limb preservation in a growing chi ld. Additional investigation is underway regarding limb lengthening and oth er dynamic applications.