title: Dynamic locking screw improves fixation strength in osteoporotic bone: an in vitro study on an artificial bone model.
abstract: OBJECTIVE
  The novel dynamic locking screw (DLS) was developed to improve bone healing with locked-plate osteosynthesis by equalising construct stiffness at both cortices. Due to a theoretical damping effect, this modulated stiffness could be beneficial for fracture fixation in osteoporotic bone. Therefore, the mechanical behaviour of the DLS at the screw-bone interface was investigated in an artificial osteoporotic bone model and compared with conventional locking screws (LHS).
  
  
  METHODS
  Osteoporotic surrogate bones were plated with either a DLS or a LHS construct consisting of two screws and cyclically axially loaded (8,500 cycles, amplitude 420 N, increase 2 mN/cycle). Construct stiffness, relative movement, axial screw migration, proximal (P) and distal (D) screw pullout force and loosening at the bone interface were determined and statistically evaluated.
  
  
  RESULTS
  DLS constructs exhibited a higher screw pullout force of P 85 N [standard deviation (SD) 21] and D 93 N (SD 12) compared with LHS (P 62 N, SD 28, p = 0.1; D 57 N, SD 25, p < 0.01) and a significantly lower axial migration over cycles compared with LHS (p = 0.01). DLS constructs showed significantly lower axial construct stiffness (403 N/mm, SD 21, p < 0.01) and a significantly higher relative movement (1.1 mm, SD 0.05, p < 0.01) compared with LHS (529 N/mm, SD 27; 0.8 mm, SD 0.04).
  
  
  CONCLUSIONS
  Based on the model data, the DLS principle might also improve in vivo plate fixation in osteoporotic bone, providing enhanced residual holding strength and reducing screw cutout. The influence of pin-sleeve abutment still needs to be investigated.
authors.affiliation: Department of Trauma, Hand and Reconstructive Surgery, University Hospital Saarland, Saar, Germany, tim.pohlemann@uks.eu.
authors.forename: Tim
authors.initials: T
authors.lastname: Pohlemann
authors.forename: Boyko
authors.initials: B
authors.lastname: Gueorguiev
authors.forename: Yash
authors.initials: Y
authors.lastname: Agarwal
authors.forename: Dieter
authors.initials: D
authors.lastname: Wahl
authors.forename: Christoph
authors.initials: C
authors.lastname: Sprecher
authors.forename: Karsten
authors.initials: K
authors.lastname: Schwieger
authors.forename: Mark
authors.initials: M
authors.lastname: Lenz
mesh_terms: D001863:Bone Screws; D018786:Bone Substitutes; D005593:Fracture Fixation, Internal / Q000295:instrumentation*; D017102:Fracture Healing; D006801:Humans; D066298:In Vitro Techniques; D008953:Models, Anatomic; D010024:Osteoporosis / Q000601:surgery*
chemical_list: D018786:Bone Substitutes