title: The Effect of Impact Location on Force Transmission to the Modular Junctions of Dual-Taper Modular Hip Implants.
abstract: The purpose of this study was to investigate the effect that off-axis impaction has on stability of dual-taper modular implants as measured by forces delivered to and transmitted through the head-neck and neck-stem tapers, respectively.
  
  
  
  One hundred forty-four impact tests were performed using 6 different directions: one on-axis and five 10° off-axes. Four different simulations were performed measuring the head-neck only and 3 different neck angulations: 0°, 8°, and 15°. A drop tower impactor delivered both on- and off-axis impaction from a constant height. Load cells positioned in the drop mass and at the head-neck (HN) or neck-stem (NS) junction measured the impact and joint forces, respectively.
  
  
  
  Impact force of the hammer on the head ranged from 3800-4500 N. Greatest impact force delivered to the head was typically with axial impact. However, greatest force transmission to the neck-stem junction was not necessarily with axial impacts. There was limited variability in the force measured at the NS junction for all impaction directions seen in the 8° neck, whereas the 15° neck had greater forces transmitted to the NS junction with off-axes impactions directed in the proximal and posterior-proximal directions.
  
  
  
  The location of the impact significantly influences the force transmitted to the head-neck and neck-stem junctions in dual-taper modular hip implants. Although axial impacts proved superior to off-axis impacts for the straight 0° neck, greater force transmission with off-axis impacts for the angled necks suggests that off-axis impacts may potentially compromise the stability of dual-taper components.
authors.affiliation: Department of Orthopaedic Surgery, Henry Ford Health System, Detroit, Michigan.
authors.forename: Nicholas B
authors.initials: NB
authors.lastname: Frisch
authors.affiliation: Department of Orthopaedic Surgery, Henry Ford Health System, Detroit, Michigan.
authors.forename: Jonathan R
authors.initials: JR
authors.lastname: Lynch
authors.affiliation: Department of Orthopaedic Surgery, Henry Ford Health System, Detroit, Michigan.
authors.forename: Richard F
authors.initials: RF
authors.lastname: Banglmaier
authors.affiliation: Department of Orthopaedic Surgery, Henry Ford Health System, Detroit, Michigan.
authors.forename: Craig D
authors.initials: CD
authors.lastname: Silverton
mesh_terms: D019644:Arthroplasty, Replacement, Hip / Q000379:methods*; D003198:Computer Simulation; D006622:Hip Prosthesis; D006801:Humans; D008962:Models, Theoretical; D011474:Prosthesis Design; D013314:Stress, Mechanical
keywords: corrosion; fretting; impaction; modular necks; stability; total hip arthroplasty