title: Fracture near press-on interlocking enhances callus mineralisation in a sheep midshaft tibia osteotomy model.
abstract: BACKGROUND
  Factors which impair fracture healing after intramedullary (IM) nailing of long bone fractures range from surgical and biological factors to mechanical parameters. Mechanical parameters known to prolong bony consolidation are share forces at the site of the fracture. Fracture near press-on interlocking reduces share forces directly at the fracture site and is hypothesised to enhance callus mineralisation. A sheep model of midshaft tibia osteotomies evaluates the technique.
  
  
  METHODS
  Fracture near interlocking was achieved by surfacing a custom made nail with special hutches that enable firm screw seating on top of the nail ("golf ball" structure). Virtual (fine element analysis (FEA)) and biomechanical pilot tests were completed before in vivo application in 12 adult female German black sheep. Midshaft tibia osteotomy was performed creating a subcritical 7 mm gap for delay in union. One group (n=6) was treated with reamed IM nailing employing the custom made nail and in addition to proximal and distal standard interlocking a fracture near press on interlocking was employed. A second group of six sheep without additional press on interlocking served as control. 10 weeks after operation the quality of fracture healing was determined by micro-CT.
  
  
  RESULTS
  The FEA showed that axial loading up to 4000N did not lead to implant fatigue. Fracture near press on interlocking led to significantly more callus mineralisation compared to the conventional interlocking procedure (0.567 g/cm(3) ± 0.106 g/cm(3) versus 0.434 g/cm(3) ± 0.0836 g/cm(3), p=0.043).
  
  
  CONCLUSIONS
  Fracture near press on interlocking increases callus mineralisation in a subcritical osteotomy model in sheep. The results indicate that the reduction of share forces at the fracture site after nailing procedures may be effective in reducing the time until bony consolidation.
authors.affiliation: Department for Trauma and Reconstructive Surgery, University of Rostock, Germany. Electronic address: georg.gradl@med.uni-rostock.de.
authors.forename: G
authors.initials: G
authors.lastname: Gradl
authors.affiliation: Department for Trauma and Reconstructive Surgery, University of Rostock, Germany.
authors.forename: P
authors.initials: P
authors.lastname: Herlyn
authors.affiliation: Department for Trauma and Reconstructive Surgery, University of Rostock, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Emmerich
authors.affiliation: MediClin Müritz-Klinikum, Clinic for Anaestesiology and Intensive Care Medicine, Waren, Germany.
authors.forename: U
authors.initials: U
authors.lastname: Friebe
authors.affiliation: Institute of Biomedical Engineering, University of Rostock, Germany.
authors.forename: H
authors.initials: H
authors.lastname: Martin
authors.affiliation: Department for Trauma and Reconstructive Surgery, University of Rostock, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Mittlmeier
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D001858:Bone Nails; D002146:Bony Callus / Q000473:pathology*; D005260:Female; D005594:Fracture Fixation, Intramedullary; D017102:Fracture Healing; D010027:Osteotomy; D012756:Sheep; D013978:Tibial Fractures / Q000473:pathology / Q000601:surgery*
keywords: Callus mineralisation; Intramedullary nailing; Micro-CT; Midshaft tibia osteotomy; Press-on interlocking; Vascularisation