Time-dependent circumferential deformation of cortical bone upon internal radial loading

Area of Science:

• Biomedical Engineering
• Orthopedic Biomechanics
• Materials Science

Background:

• Cortical bone's mechanical properties are crucial for bone implant stability.
• Understanding bone creep response under load is essential for predicting implant longevity.
• Intramedullary loading is a common scenario for orthopedic implants.

Purpose of the Study:

• To investigate the circumferential (hoop) creep behavior of cortical bone under radial load.
• To determine if a stress threshold exists that differentiates linear and nonlinear creep responses in bone.
• To characterize the relationship between hoop stress, time, and creep strain in femoral bone cylinders.

Main Methods:

• Conducting short and long duration creep tests on hollow femoral bone cylinders.
• Applying intramedullary radial loads to induce hoop stress.
• Analyzing creep strain, creep strain rate, and residual strain.
• Assessing damage morphology and fitting data to a power-law relationship.

Main Results:

• A distinct hoop stress threshold was identified for cortical bone.
• Below the threshold, creep strain, strain rate, and residual strain showed linear behavior.
• Above the threshold, these parameters exhibited nonlinear behavior, indicating a shift in mechanical response.
• A power-law relationship effectively described creep strain as a function of hoop stress and time.

Conclusions:

• Cortical bone exhibits a stress threshold governing its creep behavior.
• Linear viscoelasticity dominates at low hoop stress, while nonlinear effects prevail above the threshold.
• The findings provide critical data for modeling bone mechanics and designing orthopedic implants.