title: Torsional stiffness in healing fractures: influence of ossification: an experimental study in rats.
abstract: BACKGROUND
  Different fracture fixation techniques and fracture environment influence bone formation in healing fractures. However, the influence on the development of biomechanical properties has not been clear described. We evaluated the influence of fracture fixation stability and fracture environment on mechanical properties in healing femoral fractures in rats.
  
  
  METHODS
  Animals were treated surgically with external fixation: 1 group (27 rats) with 0-mm fracture gap size with bone ends touching, corresponding to an axial stiffness of 265 (SD 34) N/mm, and a second group (27 rats) with 2-mm fracture gap size corresponding to an axial stiffness of 30 (SD 2.1) N/mm. From each group, 6-7 animals were killed at 2, 4, 6 and 12 weeks. Torsional test revealed a delay in torsional stiffness in fractures in group 2 compared to group 1. In group 2, the torsional stiffness of the contralateral femora was found to be greater at 12 weeks than the torsional stiffness in group 1.
  
  
  CONCLUSIONS
  We found that during fracture healing, the development of torsional stiffness corresponds to the magnitude of endochondral ossification and late response of bone formation. A significantly increased torsional stiffness in the non-fractured leg of rats with delayed fracture healing was also found, possibly indicating a response to loading conditions or a systemic stimulation of bone mass.
authors.affiliation: Department of Plastic Surgery, Göteborg University, Göteborg, Sweden. hans.mark@vgregion.se
authors.forename: Hans
authors.initials: H
authors.lastname: Mark
authors.forename: Björn
authors.initials: B
authors.lastname: Rydevik
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D005264:Femoral Fractures / Q000503:physiopathology* / Q000601:surgery; D005592:Fracture Fixation / Q000379:methods*; D017102:Fracture Healing / Q000502:physiology*; D010012:Osteogenesis / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014102:Torsion Abnormality