Imaging of the Microstructural Failure Mechanism in the Human Hip

Area of Science:

• Biomechanics
• Orthopedic Research
• Medical Imaging

Background:

• Understanding bone failure mechanisms is crucial for fracture prevention and treatment.
• Existing imaging techniques often lack the resolution or dynamic range to capture microstructural bone failure.
• Elderly individuals with lower bone mineral density are at higher risk for hip fractures.

Purpose of the Study:

• To develop and validate a protocol for in situ micro-computed tomography (micro-CT) imaging of proximal femur failure under physiological loading.
• To investigate the microstructural behavior and energy absorption capacity of elderly female femora leading to femoral neck fractures.

Main Methods:

• A novel radio-transparent compressive stage was designed for micro-CT scanning of human femora under simulated one-leg stance loading.
• Four elderly female femora (T-score range = -2.09 to -4.75) were subjected to progressively increasing loads until fracture.
• Micro-CT imaging captured 3D microstructural changes, correlated with applied load and displacement measurements.

Main Results:

• The protocol successfully induced clinically relevant sub-capital femoral neck fractures (shear and opening types).
• Bone cortex instability was observed early in loading, with subchondral bone deforming up to 16% before fracture.
• Specimens exhibited significant energy absorption capacity, with stiffness decreasing to near-zero before failure.

Conclusions:

• The developed micro-CT imaging protocol provides unprecedented insight into bone failure mechanics.
• Elderly femora demonstrate remarkable damage tolerance and synergistic interaction between cortical and trabecular bone.
• This method can advance our understanding of fracture etiology and inform therapeutic strategies.