Elective hinge and polyethylene exchange for lower limb tumor endoprostheses: Is it a good idea?

Abstract

Background Long-term survival of endoprosthetic implants is a major concern, with reported 20-year survival rates of lower limb tumor endoprostheses at only 25–38%. Mechanical failure of polyethylene (PE)-bearing surfaces may result in irreversible damage and contribute to osteolysis and aseptic loosening. The practice in our institution is to electively change replaceable parts of lower limb endoprosthesis ~7 years after index surgery. Patients and methods From 2014 to 2019, five patients underwent an elective change of parts at an average of 7 years from the initial surgery. All patients had rotating-hinge implants including one proximal tibia, three distal femurs, and one total femur prosthesis. Three had a fixed-poly (FP) with a rotating femur (Stryker GMRS), and two had a rotating mobile polyethylene (MP) design (Zimmer ZSS). PE liners, hinge pin protectors, and bushings were retrieved for analysis. The parts were examined for macroscopic wear and under a light microscope at up to 40 times magnification. Linear wear was measured at standardized points. Results There were no major perioperative complications. MP inserts showed minimal burnishing. FP liners showed macroscopically visible surface pitting and posterior edge delamination. Submillimeter linear wear was noted on PE liners, bushings, and hinge pin protectors, with minimal evidence of macroscopic wear. Conclusion Elective PE exchange is a possible option for extending the longevity of tumor endoprostheses. The optimal timing of surgery is to be determined. Our retrieval study suggests that 7 years is appropriate for the FP design but may be early for the MP design. Further studies are required to determine implant survival benefits.