Re-evaluating the toughness of human cortical bone

Area of Science:

• Biomechanics
• Materials Science
• Orthopedics

Background:

• Linear-elastic fracture mechanics (LEFM) is the standard for analyzing bone toughness.
• LEFM assumes nonlinearity is confined to a very small zone, which may not hold true for bone.
• Assessing bone quality using LEFM in clinical studies may be inaccurate.

Purpose of the Study:

• To re-analyze fracture data in human humeral cortical bone.
• To assess the validity of linear-elastic fracture mechanics (LEFM) for bone.
• To propose and validate a more accurate nonlinear fracture model for bone.

Main Methods:

• Re-analyzed existing load vs. load-point displacement data from compact-tension tests on human cortical bone.
• Calibrated a nonlinear cohesive zone fracture model against experimental data.
• Compared predictions of the nonlinear model with those of LEFM.

Main Results:

• Conventional LEFM could not accurately represent the load-displacement curves of cortical bone.
• The nonlinear cohesive zone model accurately predicted peak load and displacement.
• The nonlinear zone in cortical bone was observed to be 3-10 mm, larger than LEFM assumptions.
• LEFM-derived fracture toughness is not a material constant for bone.

Conclusions:

• LEFM is an inaccurate model for human cortical bone fracture.
• A nonlinear cohesive zone model offers a more accurate representation of bone fracture mechanics.
• The cohesive law may serve as a superior measure of bone quality, potentially aiding osteoporosis therapy assessment.