EXTENDIBLE ENDOPROSTHESES FOR THE SKELETALLY IMMATURE

Aseptic loosening was identified as the predominant cause of implant r elated failure in a retrospective study of a consecutive series of 168 Stanmore custom made extendible endoprosthetic replacements used in s keletally 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 extendib le endoprosthesis was inserted in 1976, 4 types of extension mechanism s have been used. Thirty eight of the 164 cases with followup data wer e revised, of which 19 were as a result of aseptic loosening. Survival analysis revealed that the overall probability of surviving an implan t related failure was 0.512 (+/- 0.005) at 5 years, highlighting the h igh complication rate of these extendible replacements that required a revision procedure. Sixteen of the 19 aseptic loosening cases were di stal 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 repl acement before skeletal maturity had been reached.