Effects of age and loading rate on equine cortical bone failure.

The research explored how the age of a horse and the speed at which force is applied affect the failure of bone in the horse’s leg. They found that bone is stronger but fractures more easily when force is applied quickly, and that as a horse ages, the bone becomes less tough under slow loading but doesn’t change under rapid loading.

Objective of the Research

The study aimed to fill in gaps in our understanding of bone fractures, which most often occur from impact loading such as in sporting accidents or falls. Despite these being the most common cause of fractures, few studies had tested how bone behaves under such rapid force application. It involved testing femoral samples from deceased horses aged between 6 months and 28 years.

Methodology

• The researchers carried out fracture toughness and compressive tests under both slow (quasi-static) and rapid (dynamic) loading conditions. This helped determine how the speed of the force application and the bone’s age influenced its mechanical behaviour.
• They used single and double-notch specimens in four-point bending geometry setups to measure fracture toughness and note differences in crack initiation between dynamic and quasi-static tests.
• To measure compressive properties, the team applied force parallel and perpendicular to the direction of osteonal growth.
• They utilized scanning electron and scanning confocal microscopy to analyze fracture propagation and study the impact of microstructural toughening mechanisms at different strain rates.
• The team also analyzed specimens for dry, wet, and mineral densities and weight percent mineral to establish any effects of composition on mechanical behaviour.

Major Findings

• The results indicated that bones demonstrated a higher compressive strength but lesser fracture toughness when tested dynamically compared to quasi-static tests. This suggests that bones can withstand more force but are more likely to fracture if the force is applied quickly.
• The study also discovered that fracture toughness decreases with age under quasi-static conditions but remains consistent under dynamic loading. This finding shows that the aging process predominantly weakens the bone’s ability to resist fracturing under slow loading conditions, rather than under rapid ones.