title: Dynamization at the near cortex in locking plate osteosynthesis by means of dynamic locking screws: an experimental study of transverse tibial osteotomies in sheep.
abstract: BACKGROUND
  Locking plates are widely used in fracture fixation, mainly for meta-diaphyseal fractures, comminuted fractures, fractures with a critical-size bone defect, periprosthetic fractures, osteotomies, and fractures in osteoporotic bone. The aim of this animal study was to evaluate the effect on bone-healing of dynamization of locking plate constructs by means of new 5.0-mm dynamic locking screws (in the DLS group), which allow near-cortex micromotion, compared with a more rigid construct utilizing standard bicortical locking-head screws (in the LS group). Use of dynamic locking screws allows modulation of the stiffness of existing locking compression plate systems via parallel interfragmentary micromotion.
  
  
  METHODS
  A standardized diaphyseal tibial osteotomy (90°, 3-mm fracture gap) was performed and stabilized with a six-hole large-fragment locking compression plate in twelve female sheep (six in each group). Radiographs were made postoperatively and then weekly from week three until sacrifice at nine weeks. Macroscopic, biomechanical, histologic, and radiographic assessments and microcomputed tomography were performed.
  
  
  RESULTS
  The callus in the tested specimens in the DLS group had better biomechanical stability, with a significantly greater maximum failure moment (mean and standard deviation [SD] as a percentage of intact, 55.15 ± 20.65 compared with 26.80 ± 14.96 in the LS group; p = 0.021). The DLS group also had greater periosteal callus volume at the near cortex (mean volume and SD as a percentage of the tibial shaft volume, 36.21% ± 10.08% compared with 18.98% ± 8.61% in the LS group; p = 0.026) and in the intercortical region (mean volume and SD as a percentage of the bone volume of the tibial shaft, 3.56% ± 0.52% compared with 2.64% ± 0.98% in the LS group; p = 0.045), as shown by microcomputed tomography. The DLS group also had significantly greater torsional stiffness (mean and SD as a percentage of intact, 84.88 ± 13.51 compared with 58.89 ± 20.61 in the LS group; p = 0.027).
  
  
  CONCLUSIONS
  Controlled micromotion and nearly homogeneous interfragmentary strain at the fracture site, together with the stable bicortical fixation achieved by the new dynamic locking screw, led to more uniform callus formation, significantly more callus formation at the near cortex, and biomechanically more competent bone-healing compared with use of rigid locking plate constructs with locking-head screws.
authors: Musculoskeletal Research Unit (MSRU), Equine Hospital, Vetsuisse Faculty, University of Zürich, Winterthurerstrasse 260, 8057 Zürich, Switzerland. E-mail address for H. Richter: henning.richter@uzh.ch. E-mail address for K. Klein: kklein@vetclinics.uzh.ch. E-mail address for K. Nuss: katja.nuss@vetclinics.uzh.ch. E-mail address for B. von Rechenberg: bvonrechenberg@vetclinics.uzh.ch.
authors: Henning
authors: H
authors: Richter
authors: Trauma Hospital Graz UKH), Göstinger Strasse 24, 8021 Graz, Austria. E-mail address: Michael.Plecko@usz.ch.
authors: Michael
authors: M
authors: Plecko
authors: Synthes GmbH, Luzernstrasse 21, 4528 Zuchwil/Solothurn, Switzerland. E-mail address for D. Andermatt: Andermatt.Daniel@synthes.com. E-mail address for R. Frigg: robert.frigg@me.com.
authors: Daniel
authors: D
authors: Andermatt
authors: Synthes GmbH, Luzernstrasse 21, 4528 Zuchwil/Solothurn, Switzerland. E-mail address for D. Andermatt: Andermatt.Daniel@synthes.com. E-mail address for R. Frigg: robert.frigg@me.com.
authors: Robert
authors: R
authors: Frigg
authors: Veterinary Anaesthesia Services International, Zürcherstrasse 39, 8400 Winterthur, Switzerland. E-mail address: peter.kronen@vas-int.com.
authors: Peter W
authors: PW
authors: Kronen
authors: Musculoskeletal Research Unit (MSRU), Equine Hospital, Vetsuisse Faculty, University of Zürich, Winterthurerstrasse 260, 8057 Zürich, Switzerland. E-mail address for H. Richter: henning.richter@uzh.ch. E-mail address for K. Klein: kklein@vetclinics.uzh.ch. E-mail address for K. Nuss: katja.nuss@vetclinics.uzh.ch. E-mail address for B. von Rechenberg: bvonrechenberg@vetclinics.uzh.ch.
authors: Karina
authors: K
authors: Klein
authors: Musculoskeletal Research Unit (MSRU), Equine Hospital, Vetsuisse Faculty, University of Zürich, Winterthurerstrasse 260, 8057 Zürich, Switzerland. E-mail address for H. Richter: henning.richter@uzh.ch. E-mail address for K. Klein: kklein@vetclinics.uzh.ch. E-mail address for K. Nuss: katja.nuss@vetclinics.uzh.ch. E-mail address for B. von Rechenberg: bvonrechenberg@vetclinics.uzh.ch.
authors: Katja
authors: K
authors: Nuss
authors: Institute for Surgical Technology and Biomechanics, University of Berne, Stauffacherstrasse 78, 3014 Berne, Switzerland. E-mail address: sferguson@ethz.ch.
authors: Stephen J
authors: SJ
authors: Ferguson
authors: Berufsgenossenschaftliche Unfallklinik Tübingen, Schnarrenbergstrasse 95, 72076 Tübingen, Germany. E-mail address: ustoeckle@bgu-tuebingen.de.
authors: Ulrich
authors: U
authors: Stöckle
authors: Musculoskeletal Research Unit (MSRU), Equine Hospital, Vetsuisse Faculty, University of Zürich, Winterthurerstrasse 260, 8057 Zürich, Switzerland. E-mail address for H. Richter: henning.richter@uzh.ch. E-mail address for K. Klein: kklein@vetclinics.uzh.ch. E-mail address for K. Nuss: katja.nuss@vetclinics.uzh.ch. E-mail address for B. von Rechenberg: bvonrechenberg@vetclinics.uzh.ch.
authors: Brigitte
authors: B
authors: von Rechenberg
mesh_terms: D000818:Animals; D001860:Bone Plates; D001863:Bone Screws; D004195:Disease Models, Animal; D005260:Female; D005593:Fracture Fixation, Internal / Q000295:instrumentation*; D017102:Fracture Healing; D010027:Osteotomy; D011859:Radiography; D012756:Sheep; D013977:Tibia / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D013978:Tibial Fractures / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*