title: Ultrasound melted polymer sleeve for improved screw anchorage in trabecular bone--A novel screw augmentation technique.
abstract: BACKGROUND
  Screw anchorage in osteoporotic bone is still limited and makes treatment of osteoporotic fractures challenging for surgeons. Conventional screws fail in poor bone quality due to loosening at the screw-bone interface. A new technology should help to improve this interface. In a novel constant amelioration process technique, a polymer sleeve is melted by ultrasound in the predrilled screw hole prior to screw insertion. The purpose of this study was to investigate in vitro the effect of the constant amelioration process platform technology on primary screw anchorage.
  
  
  METHODS
  Fresh frozen femoral heads (n=6) and vertebrae (n=6) were used to measure the maximum screw insertion torque of reference and constant amelioration process augmented screws. Specimens were cut in cranio-caudal direction, and the screws (reference and constant amelioration process) were implanted in predrilled holes in the trabecular structure on both sides of the cross section. This allowed the pairwise comparison of insertion torque for constant amelioration process and reference screws (femoral heads n=18, vertebrae n=12). Prior to screw insertion, a micro-CT scan was made to ensure comparable bone quality at the screw placement location.
  
  
  RESULTS
  The mean insertion torque for the constant amelioration process augmented screws in both, the femoral heads (44.2 Ncm, SD 14.7) and the vertebral bodies (13.5 Ncm, SD 6.3) was significantly higher than for the reference screws of the femoral heads (31.7 Ncm, SD 9.6, p<0.001) and the vertebral bodies (7.1 Ncm, SD 4.5, p<0.001).
  
  
  CONCLUSIONS
  The interconnection of the melted polymer sleeve with the surrounding trabecular bone in the constant amelioration process technique resulted in a higher screw insertion torque and can improve screw anchorage in osteoporotic trabecular bone.
authors.affiliation: Department of Trauma Surgery, Medical University of Innsbruck, Innsbruck, Austria. Electronic address: werner.schmoelz@i-med.ac.at.
authors.forename: W
authors.initials: W
authors.lastname: Schmoelz
authors.affiliation: Department of Trauma Surgery, Medical University of Innsbruck, Innsbruck, Austria. Electronic address: raul.mayr@tirol-kliniken.at.
authors.forename: R
authors.initials: R
authors.lastname: Mayr
authors.affiliation: Thommen Medical, Neckarsulmstrasse 28, Grenchen 2540, Switzerland. Electronic address: Falko.Schlottig@nexilis.ch.
authors.forename: F
authors.initials: F
authors.lastname: Schlottig
authors.affiliation: Department of Trauma Surgery, Medical University of Innsbruck, Innsbruck, Austria. Electronic address: Nikola.Ivanovic@i-med.ac.at.
authors.forename: N
authors.initials: N
authors.lastname: Ivanovic
authors.affiliation: Division of Clinical and Functional Anatomy, Department of Anatomy, Medical University of Innsbruck, Innsbruck, Austria. Electronic address: Romed.Hoermann@i-med.ac.at.
authors.forename: R
authors.initials: R
authors.lastname: Hörmann
authors.affiliation: Institute for Biomechanics, ETH Zurich, Switzerland. Electronic address: jgoldhahn@ethz.ch.
authors.forename: J
authors.initials: J
authors.lastname: Goldhahn
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D001863:Bone Screws; D002102:Cadaver; D004867:Equipment Design; D004868:Equipment Failure; D005270:Femur Head / Q000601:surgery; D006801:Humans; D058866:Osteoporotic Fractures / Q000601:surgery*; D011108:Polymers; D013131:Spine / Q000601:surgery; D019415:Torque; D014463:Ultrasonography
chemical_list: D011108:Polymers
keywords: Augmentation; Bone amelioration; Insertion torque; Primary stability; Screw anchorage; Trabecular bone