M Hosseinitabatabaei, N Soltan, M McDonald, C Kawalilak,

G Johnston, S Kontulainen, JD Johnston

Validating FE predictions of distal radius failure load: standard region and 4% region

Fixed Scan Position vs Relative Scan Position

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Bonaretti et al1 recently recommended imaging at the 4% site of the distal radius instead of the standard fixed scan site

Benefits:

Avoids measurement bias related to bone length variability

Compare to existing reference data (e.g., pQCT data, other HR-pQCT data from 4% site)

1. Bonaretti et al (2017), Osteoporosis Int

Finite Element (FE) Modeling

3

Experimental studies validating finite element (FE) predictions of distal radius bone failure load2 and other strength metrics3 have evaluated the standard site

Unclear if FE predictions acquired from the 4% site accurately predict distal radius failure load

2. Mueller et al (2011), Osteoporosis Int 3. MacNeil & Boyd (2008), Bone

Objective

Primary objective:

Evaluate FE-predictions of distal radius failure load acquired from the standard region and the 4% region in relation to experimental failure load

Secondary objective:

Compare FE-predictions of distal radius failure load acquired from the standard region and the 4% region

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Objective

Primary objective:

Evaluate FE-predictions of distal radius failure load acquired from the standard region and the 4% region in relation to experimental failure load

Secondary objective:

Compare FE-predictions of distal radius failure load acquired from the standard region and the 4% region

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Methods – Samples

Acquired 19 female, fresh-frozen cadaveric arms (age: 84 ± 8.3 years)

Arms were intact and extended from finger-tip to mid-humerus

Radius measured from radial head to tip of radial styloid process

Soft tissue was removed from radius and ulna

Forearms were potted (fixated) midshaft in PMMA4

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4. Edwards & Troy (2012), Medical Engineering & Physics

Methods – Samples

Acquired 19 female, fresh-frozen cadaveric arms (age: 84 ± 8.3 years)

Arms were intact and extended from finger-tip to mid-humerus

Radius measured from radial head to tip of radial styloid process

Soft tissue was removed from radius and ulna

Forearms were potted (fixated) midshaft in PMMA4

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4. Edwards & Troy (2012), Medical Engineering & Physics

Methods – HR-pQCT Imaging

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First generation XtremeCT with an isotropic voxel size of 82 µm

First scan: Standard region of interest (ROI) located 9.5mm proximal to the reference line

Second scan: 9 blocks starting from the standard reference line

Employed Bonaretti’s “skier” approach1 to identify the 4% site

Reference line

Standard clinical ROI

9-b

lock

RO

I

1. Bonaretti et al (2017), Osteoporosis Int

Methods – HR-pQCT Imaging

First generation XtremeCT with an isotropic voxel size of 82 µm

First scan: Standard region of interest (ROI) located 9.5mm proximal to the reference line

Second scan: 9 blocks starting from the standard reference line

Employed Bonaretti’s “skier” approach1 to identify the 4% site

1. Bonaretti et al (2017), Osteoporosis Int

Methods – HR-pQCT Imaging

Standard reference line

Proximal tip reference line

4% Region

4%

First generation XtremeCT with an isotropic voxel size of 82 µm

First scan: Standard region of interest (ROI) located 9.5mm proximal to the reference line

Second scan: 9 blocks starting from the standard reference line

Employed Bonaretti’s “skier” approach1 to identify the 4% site

1. Bonaretti et al (2017), Osteoporosis Int

Methods – HR-pQCT Imaging

First generation XtremeCT with an isotropic voxel size of 82 µm

First scan: Standard region of interest (ROI) located 9.5mm proximal to the reference line

Second scan: 9 blocks starting from the standard reference line

Employed Bonaretti’s “skier” approach1 to identify the 4% site

Standard reference line

4% 9.5mm

Standard Region

1. Bonaretti et al (2017), Osteoporosis Int

Methods – FE Analysis x y

z Uz

Employed the single tissue FE model

Young’s Modulus: 6.829 GPa 3

Poisson’s ratio: 0.3

High-friction axial compression

Pistoia’s failure criteria5

Failure load defined as the load leading to 2% of bone tissue exceeding an energy equivalent strain of 7000 µstrain

3. MacNeil & Boyd (2008), Bone 5. Pistoia et al (2002), Bone

Methods – FE Analysis

Employed the single tissue FE model

Young’s Modulus: 6.829 GPa 3

Poisson’s ratio: 0.3

High-friction axial compression

Pistoia’s failure criteria4

Failure load defined as the load leading to 2% of bone tissue exceeding an energy equivalent strain of 7000 µstrain

0 mstrain 7000 mstrain

3. MacNeil & Boyd (2008), Bone 5. Pistoia et al (2002), Bone

Methods - Experimental Testing

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Forearms mounted vertically (axial compression) with 0° dorsal inclination and 3-6° radial inclination6

Compression testing performed at 3mm/s until failure 4,5

Determined ultimate failure load from experimental data

4. Edwards & Troy (2012), Medical Engineering & Physics 5. Pistoia et al (2002), Bone

6. Lochmuller et al (2008), JBMR

Methods - Experimental Testing

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Forearms mounted vertically (axial compression) with 0° dorsal inclination and 3-6° radial inclination6

Compression testing performed at 3mm/s until failure 4,5

Determined ultimate failure load from experimental data

4. Edwards & Troy (2012), Medical Engineering & Physics 5. Pistoia et al (2002), Bone

6. Lochmuller et al (2008), JBMR

Methods - Experimental Testing

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Forearms mounted vertically (axial compression) with 0° dorsal inclination and 3-6° radial inclination

Compression testing performed at 3mm/s until failure

Determined ultimate failure load from experimental data

Ultimate Failure Load

Methods - Statistics

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Linear regression used to assess relationships between FE-derived and experimentally derived failure loads

Paired t-test used to compare FE-derived failure load of the standard region and the 4% region

Results 14 specimens experienced a Colles-type distal radius fracture

5 specimens were excluded

Wrist dislocation (n=2)

Scaphoid fracture (n=1)

Ulna fracture (n=1)

Hand fracture (n=1)

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Results

R² = 0.69

0

1

2

3

4

5

0 1 2 3 4 5E

xper

imen

tal

Fai

lure

Load

[kN

]

FE Failure Load [kN]

Bone failure load (kN)

R² = 0.72

0

1

2

3

4

5

0 1 2 3 4 5

Exper

imen

tal

Fai

lure

Load

[kN

]

FE Failure Load [kN]

Bone failure load (kN)

4% VOI Standard VOI

Standard region and 4% region offered similar predictions of distal radius failure load

FE-derived failure load of the standard region and the 4% region did not differ (p = 0.58)

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Standard region and 4% region explained similar variance in experimentally-derived distal radius failure load

Findings indicate that either region can be used to estimate distal radius failure load using HR-pQCT and FE

Discussion

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Study Strengths

Representative experimental loading configuration

Tested intact wrist joint

Utilized fresh-frozen specimens

Study Limitations

Small sample size (n=14)

Study only included postmenopausal women

Slow testing speed (3 mm/s)

Measured radius length vs ulna length used by Bonaretti et al1

Discussion

1. Bonaretti et al (2017), Osteoporosis Int

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Study Strengths

Representative experimental loading configuration

Tested intact wrist joint

Utilized fresh-frozen specimens

Study Limitations

Small sample size (n=14)

Study only included postmenopausal women

Slow testing speed (3 mm/s)

Measured radius length vs ulna length used by Bonaretti et al1

Discussion

1. Bonaretti et al (2017), Osteoporosis Int

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Future Research

Additional mechanical testing

Investigate different modeling approaches and failure criteria

Repeat study with off-axis experimental data

Discussion

Conclusions

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Standard region and 4% region explained similar variance in experimentally-derived distal radius failure load

Results indicate that either region can be used to estimate distal radius failure load using HR-pQCT and FE

Acknowledgements

Natural Sciences and Engineering Research Council (NSERC)

Saskatchewan Health Research Foundation (SHRF)

Student assistants from the Musculoskeletal & Orthopaedic Biomechanical Imaging Laboratory (MOBIL), including: Dustin Eichhorn, Nima Ashjaee, Amy Bunyamin, Mehrdad Hosseini

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Questions?