title: The effect of cross-sectional stem shape on the torsional stability of cemented implant components.
abstract: Stability of a cemented implant, once the stem-cement interface has debonded, is reliant upon stem geometry and surface finish. There are relatively few studies addressing the effect of cross-sectional stem shape on cemented implant fixation. The purpose of this investigation was to compare the torsional stability of five different stem cross-sectional shapes-circular, oval, triangular, rectangular with rounded edges, and rectangular with sharp edges-under monotonically increasing and cyclic loading conditions. Seven samples of each stem geometry were tested. Stems were potted in bone cement and loaded to 5 deg of rotation. For monotonic loading, torque was applied at a constant rate of 2.5 deg/min. For cyclic loading, a sine wave torque pattern was applied, with a maximum magnitude that began at 4.5 Nm for 1500 cycles and then increased by 2.25 Nm every 1500 cycles until 5 deg of rotation. The rectangular stem with the sharp edges always provided the greatest resistance to torque, followed by the rectangular with rounded edges, triangular, oval, and circular. These results, including the effects of sharp corners, may differ for modes of loading other than torsion. These experimental results support the findings of earlier finite element models, indicating stem shape has a significant effect on resistance to torsional loading.
authors.affiliation: Biomechanical Testing Laboratory, Department of Mechanical and Materials Engineering, University of Western Ontario, London, Ontario N6A 5B9, Canada. akedgley@uwo.ca
authors.forename: Angela E
authors.initials: AE
authors.lastname: Kedgley
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Takaki
authors.forename: Pencilla
authors.initials: P
authors.lastname: Lang
authors.forename: Cynthia E
authors.initials: CE
authors.lastname: Dunning
mesh_terms: D001843:Bone Cements / Q000592:standards*; D002484:Cementation; D008422:Materials Testing; D011474:Prosthesis Design / Q000592:standards; D011475:Prosthesis Failure; D012399:Rotation; D013314:Stress, Mechanical; D013499:Surface Properties; D019415:Torque; D016474:Weight-Bearing
chemical_list: D001843:Bone Cements