02/03/2026
Why You Should Separate Cortical and Cancellous Bone in FEA
Introduction
When performing Finite Element Analysis (FEA) of bone structures, one common shortcut is modeling the entire bone as a single material.
It seems efficient.
But bone is not a solid block.
It is layered — and each layer behaves differently under load.
Understanding this difference is essential for accurate biomechanical simulation.
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Bone Is Like a Coconut
Think of bone like a coconut:
• The hard outer shell = cortical bone
• The softer inner structure = cancellous bone
They are part of the same object, but they serve different mechanical roles.
Cortical bone
• Dense
• Stiff
• Main load-bearing layer
Cancellous bone
• Porous
• Less stiff
• Distributes load internally
If we ignore this structure in FEA, we change how force flows through the model.
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Why Material Stiffness Matters
In linear elastic analysis, stress depends on stiffness:
σ = Eε
Where:
• σ = stress
• E = Young’s modulus
• ε = strain
Cortical bone typically has a Young’s modulus several times higher than cancellous bone.
This means:
• Cortical bone carries higher stress under the same deformation.
• Cancellous bone deforms more under load.
If we assign one averaged modulus to the entire bone:
• The model may become too stiff or too soft.
• Stress distribution may shift artificially.
• Local stress peaks may disappear or move.
This directly affects engineering decisions.
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Example 1: Implant Screw Design
When an orthopedic screw is inserted into bone:
• The threads engage strongly with the cortical layer.
• The cancellous bone provides secondary support.
If both layers are merged into one material:
• Peak stress in the thin cortical rim may be underestimated.
• Fracture risk may not be visible.
• Pull-out strength predictions may be inaccurate.
By separating the layers:
• Load transfer becomes more realistic.
• Stress concentration can be properly evaluated.
• Design improvements can be targeted more effectively.
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Example 2: Stress Shielding in Implants
Stress shielding occurs when an implant carries too much load, reducing mechanical stimulation in the surrounding bone.
The inner cancellous bone plays a key role in internal load sharing.
If not modeled separately:
• Internal strain levels may be miscalculated.
• Bone remodeling predictions may be unreliable.
• Long-term stability assessment may be incomplete.
Separating cortical and cancellous regions allows better understanding of internal load distribution.
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When Is Simplification Acceptable?
Using a single material model may be acceptable for:
• Early concept screening
• Quick comparative studies
• Cases focusing only on implant stress
However, for:
• Design validation
• Research publications
• Regulatory documentation
• Patient-specific simulation
Separating cortical and cancellous bone should be considered best practice.
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Final Thought
Biomechanical simulation is not just about generating colorful stress plots.
It is about representing biological structure in a mechanically meaningful way.
Bone is layered.
Load transfer is layered.
Your model should reflect that reality.
Separating cortical and cancellous bone is not unnecessary complexity.
It is responsible engineering.
Work With Us
If you are developing orthopedic implants or conducting biomechanical FEA and want your model to better reflect real bone structure, we can help.
At NRP Engineering Simulation, we specialize in biomechanical finite element analysis with a focus on realistic material modeling and engineering-driven decision support.
Learn more about our biomechanical simulation services at:
👉 www.nrp.co.th
Let’s build simulations that reflect reality — not assumptions.
