Torsional strength reduction due to cortical defects in bone

Area of Science:

• Orthopedic biomechanics
• Surgical planning
• Bone defect analysis

Background:

• Understanding the impact of bone defects on structural integrity is crucial for surgical procedures.
• Existing theories suggest distinct "stress riser" and "open-section" effects, but experimental validation is needed.

Purpose of the Study:

• To experimentally determine the relationship between circular defect size and torsional strength reduction in cortical bone.
• To define the "stress riser" and "open-section" effects in the context of bone defects.
• To inform surgical guidelines regarding acceptable bone defect sizes.

Main Methods:

• Development and verification of an experimental model for assessing torsional strength.
• Creation of circular defects ranging from 10% to 60% of bone diameter in sheep femora.
• Loading of bone specimens to failure to measure torsional strength and energy absorption.

Main Results:

• Defects up to 10% of bone diameter showed no significant reduction in torsional strength.
• A 20% defect resulted in a 34% decrease in torsional strength, indicative of a "stress riser" effect.
• Torsional strength decreased linearly with increasing defect size from 20% to 60%, without a discrete "open-section" threshold.
• A 50% defect led to a 62% reduction in torque strength and an 88% reduction in energy to failure.

Conclusions:

• The study challenges the concept of a discrete "open-section" effect for circular bone defects.
• Current surgical guidelines on defect size (e.g., avoiding >50% diameter) may be overly conservative based on these findings.
• The data provide valuable insights for surgical planning involving bone defect creation, such as for infection, biopsy, or prosthesis removal.