Sagittal profile has a significant impact on the explantability of well-fixed cemented stems in revision knee arthroplasty: a biomechanical comparison study of five established knee implant models.

Background: Easy revisability is gaining increasingly in importance. The removal of well-fixed cemented stems is very demanding and is often associated with increased operative morbidity. Implant design may be here a decisive impact factor, and the best way to ascertain it is experimentally. Aim of this study is to assess different cemented stems of established knee revision implants in regard to their removal capability.

Methods: Based on their sagittal profile, five stem extensions from known manufacturers were divided in conical, conical-cylindrical and cylindrical designs. The pedicles were also characterized in respect to their cross section, diameter and surface roughness. The cemented stems were dismounted six times each in a reproducible biomechanical setup. The explantation energy required was determined and statistical analyzed.

Results: The conical shaft needed significantly the slightest explantation energy with 19.2 joules (p = 0.004). There was a strong negative linear correlation between conicity proportion and explantation energy of the cemented stems (R = 0.983). The removal of the three purely cylindrical shafts-regardless of their differences in diameter, cross-sectional design and surface- was the most demanding (98.3, 105, and 116.7 joules) with only secondary differences between them.

Conclusion: The longitudinal stem profile may have a primary impact on the explantability of well-fixed cemented shafts with conical designs showing superiority. Cross-sectional profile and surface roughness had here a less decisive influence on the explantability. Surgeons can choose proper implants and removal techniques depending on potential implant-associated revision risks and re-revisions to be expected.