title: [Comparison of stability of plate fixateurs with parallel and oblique screw directions].
abstract: BACKGROUND
  One of the main failure mechanisms of modern plate fixateurs is the tearing of the whole plate-screw construct out of the osteoporotic bone. The aim of this study was to show whether an oblique screw placement can improve the fixation of the plate to the bone.
  
  
  METHODS
  A steel probe was fixed to a synthetic bone (Fa. Sawbones) with standard titanium fixed-angle screws in parallel and 55° oblique positioning. We tested the static tear force and the dynamic stability (force distance 1.4 or 1.6 mm, 610 and 900 N, frequency of force shift of 560 or 380/min). Endpoint was a visible tear of the artificial bone. In addition we performed a morphological analysis of the torn fragments.
  
  
  RESULTS
  The maximal tear force was 2.04 kN (1.95-2.13) for oblique and 2.66 kN (2.55-2.77) for parallel placement (p < 0.05). With a parallel positioning a higher number of force shifts were performed before a visual tear appeared. With parallel positioning the screw canal was torn with an intact surrounding corticalis; in oblique positioning the threads remained intact, the corticalis was torn out with a wedge.
  
  
  CONCLUSIONS
  An oblique screw positioning does not result in a higher tear force in modern plate fixateurs.
authors: Ruhr-Universität Bochum.
authors: O
authors: O
authors: Ackermann
authors: Institut für Metallurgie und Umformtechnik der Universität Duisburg-Essen, Fakultät für Ingenieurwissenschaften, Duisburg.
authors: P J
authors: PJ
authors: Mauk
authors: Institut für Metallurgie und Umformtechnik der Universität Duisburg-Essen, Fakultät für Ingenieurwissenschaften, Duisburg.
authors: T
authors: T
authors: Beuke
authors: Sportorthopädie, Sportklinik Duisburg.
authors: L
authors: L
authors: Roslawski
authors: Orthopädische Universitätsklinik im St. Josef Hospital, Kliniken der Ruhruniversität Bochum.
authors: M
authors: M
authors: Lahner
authors: Klinik für Chirurgie, Elisabeth-Krankenhaus, Essen.
authors: K
authors: K
authors: Eckert
authors: Orthopädische Universitätsklinik im St. Josef Hospital, Kliniken der Ruhruniversität Bochum.
authors: C
authors: C
authors: von Schulze Pellengahr
mesh_terms: D001860:Bone Plates; D001863:Bone Screws; D004867:Equipment Design; D004868:Equipment Failure; D005593:Fracture Fixation, Internal / Q000295:instrumentation* / Q000379:methods; D006801:Humans; D058866:Osteoporotic Fractures / Q000601:surgery*; D013718:Tensile Strength