title: Mechanical Analysis of Ultrasound-Activated Pins and Resorbable Screws: Two Different Techniques to Fixate Osteosynthesis in Craniosynostosis Surgery.
abstract: OBJECTIVE
  Ultrasound activation of resorbable pins directly into drilled holes of the calvarium was introduced to overcome the time-consuming installation in the resorbable osteosynthesis fixation in craniosynostosis surgery. There is paucity in the data comparing the mechanical properties of resorbable screws and ultrasound-activated pins produced by different manufacturers. The aim of this experimental study was to compare the mechanical properties of ultrasound-activated pins and resorbable screws.
  
  
  METHODS
  A mechanical testing machine was used to characterize the mechanical performance of screws and ultrasound pins. The screws and pins were tested individually in 2 directions with respect to the longitudinal axis: vertical, that is, axial pull-out strength and horizontal, that is, shear strength. The mean maximum strength of fixation was determined. Broken screws and pinheads were analyzed by a scanning electron microscope to determine the site of fracture.
  
  
  RESULTS
  All of the resorbable screws and pins broke at the point where the device enters bone. In pull-out testing, the mean maximum strength of the ultrasound-activated pins was 30.5 ± 5.4 N and that of the resorbable screws was 54.0 ± 0.3 N. In shear testing, the mean maximum strength of ultrasound-activated pins was 57.1 ± 20.1 N and that of the resorbable screws was 53.9 ± 0.4 N.
  
  
  CONCLUSIONS
  In their intended configuration, there is no clinically significant difference in fixation strength between ultrasound-activated pins and resorbable screws.
authors.affiliation: *Department of Plastic Surgery, Helsinki University Central Hospital, Helsinki †Aalto University, School of Electrical Engineering, Department of Electrical Engineering and Automation, Espoo, Finland.
authors.forename: Mikko J
authors.initials: MJ
authors.lastname: Savolainen
authors.forename: Antti G
authors.initials: AG
authors.lastname: Ritvanen
authors.forename: Virve S
authors.initials: VS
authors.lastname: Koljonen
authors.forename: Markus P K
authors.initials: MP
authors.lastname: Turunen
authors.forename: Hanna H
authors.initials: HH
authors.lastname: Hulkkonen
authors.forename: Vesa H O
authors.initials: VH
authors.lastname: Vuorinen
authors.forename: Junnu P
authors.initials: JP
authors.lastname: Leikola
mesh_terms: D020341:Absorbable Implants; D000818:Animals; D001860:Bone Plates; D001863:Bone Screws; D003394:Craniofacial Dysostosis / Q000601:surgery*; D003398:Craniosynostoses / Q000601:surgery*; D004195:Disease Models, Animal; D019220:High-Energy Shock Waves; D008422:Materials Testing / Q000379:methods*; D012886:Skull / Q000601:surgery*; D013314:Stress, Mechanical; D013552:Swine