Osteonal effects on elastic modulus and fatigue life in equine bone

Area of Science:

• Biomechanics
• Orthopedic Research
• Veterinary Science

Background:

• Osteons, the basic structural units of bone, undergo continuous remodeling throughout life.
• Incompletely mineralized osteons are more deformable and may influence bone's mechanical properties.
• Understanding factors affecting bone fatigue life is crucial for preventing fractures in athletic animals.

Purpose of the Study:

• To investigate the role of recently formed, incompletely mineralized osteons in enhancing the fatigue life of equine metacarpal bone.
• To determine if osteonal compliance and cement lines contribute to improved load-controlled fatigue life.
• To analyze the relationship between osteon characteristics, elastic modulus, and fatigue life.

Main Methods:

• Sixteen bone beams from thoroughbred racehorses' third metacarpus were subjected to load-controlled fatigue testing.
• Basic fuchsin-stained cross-sections were analyzed to quantify intact osteon density, area fraction, and cement line length.
• Statistical analysis correlated these microstructural parameters with elastic modulus and logarithm of fatigue life.

Main Results:

• Fatigue life (logN(F)) was negatively correlated with elastic modulus (E).
• Higher intact osteon area fraction and density were associated with lower elastic modulus.
• Increased intact osteon density and cement line density correlated with extended fatigue life relative to elastic modulus.

Conclusions:

• Bone remodeling, through the formation of compliant osteons and cement lines, enhances load-controlled fatigue life in equine metacarpal bone.
• Osteonal compliance reduces stress concentration, while cement lines act as barriers to microcrack propagation.
• These microstructural adaptations contribute to improved fracture resistance in equine limb bones.