title: [Finite element analysis for modular hemipelvic endoprosthesis during loaded gait cycle].
abstract: OBJECTIVE
  To analyze the biomechanical characteristics of modular hemipelvic endoprosthesis in gait cycle using finite element analysis method, and the effect of pubic connection plate on stress distribution.
  
  
  METHODS
  Three dimensional finite element model of periacetabular defect reconstructed with modular hemipelvic endoprosthesis was established. The hip contact forces, which were published from Free University of Berlin, under gait cycle were applied in the load of Abaqus 6.7. Then the simulation was conducted and four characteristic time points were identified, 17%, 36%, 43% and 86% of gait cycle. The von Mises stress distribution of the prosthesis was calculated. Stress concentration was ascertained and the difference of stress distribution between reconstruction with and without pubic connection plate was analyzed. The displacement and stress peak value of iliac fixation part under the four points of gait cycle were recorded; Comparison of stress on the four transverse iliac fixation screws was studied and the effect of pubic connection plate ascertained.
  
  
  RESULTS
  During the gait cycle, both the stress peak and maximum displacement occurred in the single-leg stance phase, according to 17%-36% of gait cycle. More rational stress distribution could be achieved under the reconstruction with pubic connection plate at 17% and 86% of gait cycle, representing ipsilateral and contralateral single-leg stance respectively, resulting in more even distribution. The maximum stresses of the iliac fixation part were 148.5 MPa and 270.1 MPa under the reconstruction with and without pubic connection plate, with significant difference (P=0.04); The mean displacements of the iliac fixation part were 9.3 mm and 11.7 mm with and without pubic connection plate reconstruction (P=0.03). The average stress level of iliac fixation part could be decreased to 50% and 24% for the iliac fixation screws. However, no micromotions were decreased under the reconstruction with pubic connection plate. Also no significant difference was observed for the relative shift of the iliac fixation part with and without pubic connection plate (P=0.41).
  
  
  CONCLUSIONS
  The stability of the implant could satisfy the normal walk activity. The pubic connection plate played an important role in the stability of the endoprosthesis, decreasing the stress peak and elongation of the durability.
authors.affiliation: Musculoskeletal Tumor Center, Peking University People's Hospital, Beijing 100044, China.
authors.forename: Tao
authors.initials: T
authors.lastname: Ji
authors.forename: Wei
authors.initials: W
authors.lastname: Guo
authors.forename: Xiao-dong
authors.initials: XD
authors.lastname: Tang
authors.forename: Sen
authors.initials: S
authors.lastname: Dong
mesh_terms: D001696:Biomechanical Phenomena; D003198:Computer Simulation; D020342:Finite Element Analysis; D005684:Gait / Q000502:physiology*; D006801:Humans; D010384:Pelvic Bones / Q000502:physiology / Q000601:surgery*; D019736:Prostheses and Implants; D019919:Prosthesis Implantation; D013314:Stress, Mechanical; D016474:Weight-Bearing / Q000502:physiology