title: Determination of rat vertebral bone compressive fatigue properties in untreated intact rats and zoledronic-acid-treated, ovariectomized rats.
abstract: CONCLUSIONS
  Compressive fatigue properties of whole vertebrae, which may be clinically relevant for osteoporotic vertebral fractures, were determined in untreated, intact rats and zoledronic-acid-treated, ovariectomized rats. Typical fatigue behavior was found and was similar to that seen in other species. Fatigue properties were comparable between both groups.
  
  
  BACKGROUND
  Osteoporosis is often treated with bisphosphonates, which reduce fracture risk. Effects of bisphosphonates on fatigue strength, which may be clinically relevant for vertebral fractures, are unknown. We determined vertebral, compressive fatigue properties in normal and zoledronic acid (ZOL)-treated, OVX rats.
  
  
  METHODS
  Thirty-five-week old Wistar rats were divided into SHAM-OVX (n = 7) and OVX with ZOL treatment (n = 5; single injection, 20 microg/kg b.w. s.c.). After 16 weeks, vertebral trabecular microarchitecture and cortical thickness were determined using micro-CT. Vertebrae were cyclically compressed in load-control at 2 Hz starting at 0.75% apparent strain. A line parallel to the apparent strain curve was drawn at 0.5% higher offset, after which the intersection was defined as the time to failure and the apparent strain at failure. Data were compared using Student's t test.
  
  
  RESULTS
  Morphology and fatigue properties were the same in both groups. Samples failed between 10 min and 15 h. Force-displacement curves displayed typical fatigue behavior. Displacement increased over time due to mostly creep and to decreasing secant stiffness.
  
  
  CONCLUSIONS
  We established a technique to determine compressive fatigue properties in the rat vertebral body. Our initial results indicate that ZOL-treated OVX rats have similar vertebral fatigue properties as SHAM-OVX controls.
authors.affiliation: Eindhoven University of Technology, Eindhoven, The Netherlands.
authors.forename: J E M
authors.initials: JE
authors.lastname: Brouwers
authors.forename: M
authors.initials: M
authors.lastname: Ruchelsman
authors.forename: B v
authors.initials: Bv
authors.lastname: Rietbergen
authors.forename: M L
authors.initials: ML
authors.lastname: Bouxsein
mesh_terms: D000818:Animals; D050071:Bone Density Conservation Agents / Q000494:pharmacology*; D019245:Compressive Strength / Q000187:drug effects; D004164:Diphosphonates / Q000494:pharmacology*; D005260:Female; D007093:Imidazoles / Q000494:pharmacology*; D010024:Osteoporosis / Q000150:complications / Q000503:physiopathology; D010052:Ovariectomy; D051381:Rats; D017208:Rats, Wistar; D016103:Spinal Fractures / Q000209:etiology / Q000503:physiopathology; D013131:Spine / Q000187:drug effects* / Q000503:physiopathology; D055114:X-Ray Microtomography; D000077211:Zoledronic Acid
chemical_list: D050071:Bone Density Conservation Agents; D004164:Diphosphonates; D007093:Imidazoles; D000077211:Zoledronic Acid