title: Volar fixed-angle plating of extra-articular distal radius fractures--a biomechanical analysis comparing threaded screws and smooth pegs.
abstract: BACKGROUND
  Distal radius fractures represent the most common fractures in adult individuals. Volar fixed-angle plating has become a popular modality for treating unstable distal radius fractures. Most of the plates allow insertion of either threaded locking screws or smooth locking pegs. To date, no biomechanical studies compare locking screws and pegs under axial and torsional loading.
  
  
  METHODS
  Ten Sawbones radii were used to simulate an AO/OTA A3 fracture. Volar fixed-angle plates (Aptus Radius 2.5, Medartis, Switzerland) with threaded locking screws (n = 5) or smooth locking pegs (n = 5) were used to fix the distal metaphyseal fragment. Each specimen was tested under axial compression and under torsional load with a servohydraulic testing machine. Qualitative parameters were recorded as well as axial and torsional stiffness, torsion strength, energy absorbed during monotonic loading and energy absorbed in one cycle.
  
  
  RESULTS
  Axial stiffness was comparable between both groups (p = 0.818). If smooth pegs were used, a 17% reduction of torsional stiffness (p = 0.017) and a 12% reduction of minimum torque (p = 0.012) were recorded. A 12% reduction of energy absorbed (p = 0.013) during monotonic loading and unloading was recorded if smooth pegs were used. A 34% reduction of energy absorbed in one cycle (p < 0.007) was recorded if threaded screws were used. Sliding of the pegs out of the distal radius metaphyses of the synthetic bones was recorded at a mean torque of 3.80 Nm ± 0.19 Nm. No sliding was recorded if threaded screws were used.
  
  
  CONCLUSIONS
  According to the results of this study using Sawbones, volar fixed-angle plates with threaded locking screws alone are mechanically superior to volar fixed-angle plates with smooth locking pegs alone under torsional loading.
authors.affiliation: Lorenz Boehler Trauma Hospital, Ludwig Boltzmann Institute for Experimental and Clinical Traumatology, Cluster for Tissue Regeneration, Vienna, Austria. patrick.weninger@gmx.net
authors.forename: Patrick
authors.initials: P
authors.lastname: Weninger
authors.forename: Enrico
authors.initials: E
authors.lastname: Dall'Ara
authors.forename: Martin
authors.initials: M
authors.lastname: Leixnering
authors.forename: Christoph
authors.initials: C
authors.lastname: Pezzei
authors.forename: Harald
authors.initials: H
authors.lastname: Hertz
authors.forename: Herwig
authors.initials: H
authors.lastname: Drobetz
authors.forename: Heinz
authors.initials: H
authors.lastname: Redl
authors.forename: Philippe
authors.initials: P
authors.lastname: Zysset
mesh_terms: D001696:Biomechanical Phenomena; D001860:Bone Plates; D001863:Bone Screws; D002102:Cadaver; D005593:Fracture Fixation, Internal / Q000295:instrumentation*; D006801:Humans; D053401:Palmar Plate / Q000601:surgery*; D011474:Prosthesis Design; D011884:Radius / Q000601:surgery*; D011885:Radius Fractures / Q000503:physiopathology / Q000601:surgery*; D019415:Torque; D016474:Weight-Bearing / Q000502:physiology*; D014955:Wrist Joint / Q000503:physiopathology / Q000601:surgery