title: Concave polyethylene component improves biomechanical performance in lumbar total disc replacement--modified compressive-shearing test by finite element analysis.
abstract: Failure of ultra-high molecular weight polyethylene components after total disc replacements in the lumbar spine has been reported in several retrieval studies, but immediate biomechanical evidence for those mechanical failures remained unclear. Current study aimed to investigate the failure mechanisms of commercial lumbar disc prostheses and to enhance the biomechanical performances of polyethylene components by modifying the articulating surface into a convex geometry. Modified compressive-shearing tests were utilized in finite element analyses for comparing the contact, tensile, and shearing stresses on two commercial disc prostheses and on a concave polyethylene design. The influence of radial clearance on stress distributions and prosthetic stability were considered. The modified compressive-shearing test revealed the possible mechanisms for transverse and radial cracks of polyethylene components, and would be helpful in observing the mechanical risks in the early design stage. Additionally, the concave polyethylene component exhibited lower contact and shearing stresses and more acceptable implant stability when compared with the convex polyethylene design through all radial clearances. Use of a concave polyethylene component in lumbar disc replacements decreased the risk of transverse and radial cracks, and also helped to maintain adequate stability. This design concept should be considered in lumbar disc implant designs in the future.
authors.affiliation: Orthopaedic Biomechanics Laboratory, Institute of Biomedical Engineering, National Yang Ming University, Taipei, Taiwan.
authors.forename: Wen-Chuan
authors.initials: WC
authors.lastname: Chen
authors.forename: Yu-Liang
authors.initials: YL
authors.lastname: Liu
authors.forename: Kun-Jhih
authors.initials: KJ
authors.lastname: Lin
authors.forename: Colin Joseph
authors.initials: CJ
authors.lastname: McClean
authors.forename: Hung-Jen
authors.initials: HJ
authors.lastname: Lai
authors.forename: Chi-Wei
authors.initials: CW
authors.lastname: Chou
authors.forename: Tsung-Wei
authors.initials: TW
authors.lastname: Chang
authors.forename: Chan-Tsung
authors.initials: CT
authors.lastname: Yang
authors.forename: Chang-Hung
authors.initials: CH
authors.lastname: Huang
authors.forename: Yu-Shu
authors.initials: YS
authors.lastname: Lai
authors.forename: Cheng-Kung
authors.initials: CK
authors.lastname: Cheng
mesh_terms: D001672:Biocompatible Materials; D001696:Biomechanical Phenomena; D019245:Compressive Strength; D020342:Finite Element Analysis; D008159:Lumbar Vertebrae / Q000601:surgery*; D008422:Materials Testing; D020959:Polyethylene; D033081:Shear Strength; D013314:Stress, Mechanical; D013499:Surface Properties; D013718:Tensile Strength; D059145:Total Disc Replacement
chemical_list: D001672:Biocompatible Materials; D020959:Polyethylene