title: Effect of Stabilization on the Healing Process of Femur Fractures in Aged Mice.
abstract: BACKGROUND
  The influence of mechanical stability on fracture healing has previously been studied in adult mice, but is poorly understood in aged animals. Therefore, we herein studied the effect of stabilization on the healing process of femur fractures in aged mice.
  
  
  METHODS
  Twenty-four 18-month-old CD-1 mice were stabilized after midshaft fracture of the femur with an intramedullary screw. In another 24 18-month-old mice, the femur fractures were left unstabilized. Bone healing was studied by radiological, biomechanical, histomorphometric, and protein expression analyses.
  
  
  RESULTS
  After 2 and 5 weeks of healing, the callus of nonstabilized fractures compared to stabilized fractures was significantly larger, containing a significantly smaller amount of osseous tissue and a higher amount of cartilaginous tissue. This was associated with a significantly lower biomechanical stiffness during the early phase of healing. However, during the late phase of fracture healing both nonstabilized and stabilized fractures showed a biomechanical stiffness of ∼40%. Of interest, Western blot analyses of callus tissue demonstrated that the expression of proteins related to angiogenesis, bone formation and remodeling, i.e. VEGF, CYR61, BMP-2, BMP-4, Col-2, Col-10, RANKL, OPG, did not differ between nonstabilized and stabilized fractures.
  
  
  CONCLUSIONS
  Nonstabilized fractures in aged mice show delayed healing and remodeling. This is not caused by an altered protein expression in the callus but rather by the excessive interfragmentary movements.
authors.affiliation: a Department of Trauma, Hand and Reconstructive Surgery , Saarland University , D-66421 Homburg/Saar, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Histing
authors.affiliation: a Department of Trauma, Hand and Reconstructive Surgery , Saarland University , D-66421 Homburg/Saar, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Heerschop
authors.affiliation: a Department of Trauma, Hand and Reconstructive Surgery , Saarland University , D-66421 Homburg/Saar, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Klein
authors.affiliation: b Institute for Clinical & Experimental Surgery , Saarland University , Homburg/Saar, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Scheuer
authors.affiliation: a Department of Trauma, Hand and Reconstructive Surgery , Saarland University , D-66421 Homburg/Saar, Germany.
authors.forename: D
authors.initials: D
authors.lastname: Stenger
authors.affiliation: a Department of Trauma, Hand and Reconstructive Surgery , Saarland University , D-66421 Homburg/Saar, Germany.
authors.forename: S C
authors.initials: SC
authors.lastname: Herath
authors.affiliation: a Department of Trauma, Hand and Reconstructive Surgery , Saarland University , D-66421 Homburg/Saar, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Pohlemann
authors.affiliation: b Institute for Clinical & Experimental Surgery , Saarland University , Homburg/Saar, Germany.
authors.forename: M D
authors.initials: MD
authors.lastname: Menger
mesh_terms: D000367:Age Factors; D000818:Animals; D001696:Biomechanical Phenomena; D002146:Bony Callus / Q000378:metabolism*; D004195:Disease Models, Animal; D005264:Femoral Fractures / Q000601:surgery*; D005592:Fracture Fixation; D017102:Fracture Healing / Q000502:physiology*; D006801:Humans; D051379:Mice; D010012:Osteogenesis / Q000502:physiology; D053245:RANK Ligand; D011859:Radiography
chemical_list: D053245:RANK Ligand
keywords: aging; bone remodeling; fracture; mechanical stability; nonstabilization; stabilization