title: More is not necessarily better. A biomechanical study on distal screw numbers in volar locking distal radius plates.
abstract: BACKGROUND
  Currently available volar locking plates for the treatment of distal radius fractures incorporate at least two distal screw rows for fixation of the metaphyseal fragment and have a variable-angle locking mechanism which allows placement of the screws in various directions There is, however no evidence that these plates translate into better outcomes or have superior biomechanical properties to first generation plates, which had a single distal screw row and fixed-angle locking. The aim of our biomechanical study was to compare fixed-angle single-row plates with variable-angle multi-row plates to clarify the optimal number of locking screws.
  
  
  METHODS
  Five different plate-screw combinations of three different manufacturers were tested, each group consisting of five synthetic fourth generation distal radius bones. An AO type C2 fracture was created and the fractures were plated according to each manufacturer's recommendations. The specimens then underwent cyclic and load-to-failure testing. An optical motion analysis system was used to detect displacement of fragments.
  
  
  RESULTS
  No significant differences were detected after cyclic loading as well as after load-to-failure testing, neither in regard to axial deformation, implant rigidity or maximum displacement. The fixed-angle single-row plate showed the highest pre-test rigidity, least increase in post-testing rigidity and highest load-to-failure rigidity and least radial shortening. The radial shortening of plates with two distal screw rows was 3.1 and 4.3 times higher, respectively, than that of the fixed-angle single-row plate.
  
  
  CONCLUSIONS
  The results of our study indicate that two distal screw rows do not add to construct rigidity and resistance against loss of reduction. Well conducted clinical studies based on the findings of biomechanical studies are necessary to determine the optimal number of screws necessary to achieve reproducibly good results in the treatment of distal radius fractures.
authors.affiliation: Department of Orthopaedic Surgery and James Cook University School of Medicine, Mackay Base Hospital, Queensland, Australia. drobo@aon.at
authors.forename: Herwig
authors.initials: H
authors.lastname: Drobetz
authors.forename: Patrick
authors.initials: P
authors.lastname: Weninger
authors.forename: Caroline
authors.initials: C
authors.lastname: Grant
authors.forename: Clare
authors.initials: C
authors.lastname: Heal
authors.forename: Reinhold
authors.initials: R
authors.lastname: Muller
authors.forename: Michael
authors.initials: M
authors.lastname: Schuetz
authors.forename: Minh
authors.initials: M
authors.lastname: Pham
authors.forename: Roland
authors.initials: R
authors.lastname: Steck
mesh_terms: D000704:Analysis of Variance; D001696:Biomechanical Phenomena; D001860:Bone Plates; D001863:Bone Screws; D004867:Equipment Design; D005593:Fracture Fixation, Internal / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D008422:Materials Testing; D053401:Palmar Plate; D011885:Radius Fractures / Q000473:pathology / Q000601:surgery*; D015203:Reproducibility of Results; D013314:Stress, Mechanical