Use of the XXXX forelimb compression model to create discrete levels of bone damage in vivo.

@entity3604 @entity174 @entity16 @entity35 @entity1642
Skeletal responses to damage are significant for understanding the etiology of @entity1642 and possibly @entity3604 . We refined the @entity35 forelimb-loading model to produce a range of sub- @entity174 damage levels during in vivo cyclic loading. A total of 98 right forelimbs of anesthetized, male, 5-month old Fischer @entity35 were loaded cyclically (2 Hz) in axial compression. @entity35 were killed immediately after loading. In the first experiment, forelimbs were loaded to @entity174 , which occurred after an increase in peak displacement of 2.0+/-0.2 mm, independent of peak force or cycle number. In the next experiment, we loaded forelimbs at a constant peak force until the peak displacement increased by 0.6-1.8 mm (30-90% of @entity174 ). Mechanical properties of the loaded (right) and contralateral control (left) ulnae were determined ex vivo using three-point bending, and cracks were analyzed using micro-computed tomography. Results demonstrated a dose-response between increased forelimb displacement and @entity16 , with four discrete damage levels. "Low" damage was produced by cyclic loading to 30% of @entity174 , with no visible cracks and a 10% strength loss. "Mild" damage was produced by loading to 45% of @entity174 , with variable linear cracks and 20% strength loss. "Moderate" damage was produced by loading to 60-75% of @entity174 , with consistent linear cracks and 40% strength loss. "High" damage was produced by loading to 85-90% of @entity174 , with branching cracks and 60% strength loss. This loading model will be useful for examining biological responses to a range of sub- @entity174 damage levels in future experiments.
