Extendible Endoprostheses for the Skeletally Immature

Abstract

Aseptic loosening was identified as the predominant cause of implant related failure in a retrospective study of a consecutive series of 168 Stanmore custom made extendible endoprosthetic replacements used in skeletally immature patients. Most of the replacements were used in the treatment of bone tumor and the remainder for the revision of failed massive endoprosthetic replacements. Since the first Stanmore extendible endoprosthesis was inserted in 1976, 4 types of extension mechanisms have been used. Thirty eight of the 164 cases with followup data were revised, of which 19 were as a result of aseptic loosening. Survival analysis revealed that the overall probability of surviving an implant related failure was 0.512 (+/- 0.005) at 5 years, highlighting the high complication rate of these extendible replacements that required a revision procedure. Sixteen of the 19 aseptic loosening cases were distal femoral replacements. The probability of a patient with a distal femoral replacement surviving aseptic loosening was 0.773 (+/- 0.008) at 5 years. Other modes of implant related failure included jamming of the extending mechanism, infection, and maximum extension of the replacement before skeletal maturity had been reached.