• Alexander Maslaris, Frank Layher, Olaf Brinkmann, Matthias Bungartz, Timo Zippelius, and Georg Matziolis.
• Department of Orthopedics, Friedrich-Schiller-University of Jena, Campus Eisenberg, Klosterlausnitzer Straße 81, 07607, Eisenberg, Germany. alexander_maslaris@hotmail.com.
• Arch Orthop Trauma Surg. 2018 Dec 1; 138 (12): 1747-1754.

BackgroundAccording to literature, more than 30% of revised knee arthroplasties will require at least one re-revision. Practical experience has shown that there are considerable product-specific differences in the explantability of cemented long-stem prostheses. In the registers of successful implants, stem geometry varies considerably between the manufacturers. However, comparative data on explantability of the respective stems are missing. Objective of the present study was to identify a correlation between the geometry of a smooth cemented long stem and the necessary explantation energy required until failure of the implant-cement interface occurs.MethodsEight cemented stems with different conical profile angles (0°-3°) were explanted in a reproducible biomechanical setup each six times to evaluate the correlation between the stem design and the required explantation energy.ResultsThe average explantation energy was highest in the case of the cylindrical stem, at 18.1 ± 3.6 J. At a cone angle of 0.25°, it was just 12.1 ± 2.1 J (p < 0.001) and dropped beyond 0.5° to an average of 5.7 ± 1.8 J (p < 0.001). Between 0.5° and 3°, no significant difference in the required extraction energy was observed.ConclusionsWhereas smooth conical stems can mostly be removed easily, an early decision in favour of osteotomy or fenestration can be taken in the case of cylindrical cemented stems.

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