Micromotion and Stress Shielding Between Taper Fluted and Cylindrical Femoral Stems for Paprosky Bone Deficiency Type IIIB

Abstract

Purpose: Taper fluted and cylindrical femoral stems have been commonly used for revision surgery with femoral bone loss. Shape and material differences between taper fluted and cylindrical confused surgeons whether superiority and inferiority in comparisons especially for type IIIB Paprosky bone deficiency. This study aims to investigate the micromotion between implant and bone interface and stress distribution around the implant in human cadaveric experiments.Methods: Paired comparisons of 7 cadavers between taper fluted stem and cylindrical stem were tested under dynamic cyclic loading. Results:The results showed appropriate bone-implant micromotions for bone osteointegration could be observed between both taper fluted and cylindrical stems (85±10m and 113±80m respectively, p=0.59). Taper fluted stem attained the load distribution from the proximal to distal surrounding bone (from 4.92±2.87MPa to 2.14±1.43MPa, p=0.43), while the cylindrical stem type obviously showed the proximal bone stress shielding (from 2.56±0.76MPa to 5.23±0.77MPa, p=0.03). Conclusion:Both taper fluted and cylindrical stems are feasible for Paprosky type IIIB reconstruction. However, the taper fluted stem is preferred since it seems to have better bone-implant stability and no further proximal surrounding bone stress shielding, especially for the thin femoral cortex. Be aware of over-reaming and appropriate stem diameter selection are crucial to prevent an early subsidence for the taper fluted stem.