Stress fracture of bone under physiological multiaxial cyclic loading: Activity-based predictive models.

Area of Science:

• Biomechanics
• Orthopedics
• Materials Science

Background:

• Excessive fatigue damage from daily activities contributes to bone fracture.
• Current uniaxial loading models overestimate bone fatigue life, limiting effective fracture management strategies.

Purpose of the Study:

• Develop a physiologically relevant model for bone failure under multiaxial cyclic loading.
• Investigate the efficacy of engineering failure criteria for predicting tibial fractures.

Main Methods:

• Utilized four engineering failure criteria (Von Mises, Tsai-Wu, Findley critical plane, maximum shear strain) on human tibiae from cadavers (ages 21-85).
• Analyzed failure criteria effectiveness in combined and age-stratified donor groups (younger: 21-52, older: 57-85).
• Validated the maximum shear strain model using published in vivo human data.

Main Results:

• All four failure criteria effectively modeled in vitro tibial fracture (r² > 0.84 combined, r² > 0.83 stratified).
• Older age groups exhibited significantly lower fatigue curves across all criteria (p < 0.001).
• The maximum shear strain model predicted in vivo failure cycles (5,000-200,000) and showed a 3-fold reduction in fatigue life for older donors.

Conclusions:

• Engineering failure criteria provide effective in vitro models for multiaxial bone loading and fracture prediction.
• Age-related bone changes significantly increase susceptibility to fatigue-induced fractures.
• These findings improve fatigue life estimations and inform fracture management strategies.