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

Transcription

1 Validating FE predictions of distal radius failure load: standard region and 4% region M Hosseinitabatabaei, N Soltan, M McDonald, C Kawalilak, G Johnston, S Kontulainen, JD Johnston

2 Fixed Scan Position vs Relative Scan Position Bonaretti et al 1 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 HRpQCT data from 4% site) 2 1. Bonaretti et al (2017), Osteoporosis Int

3 2. Mueller et al (2011), Osteoporosis Int 3. MacNeil & Boyd (2008), Bone Finite Element (FE) Modeling Experimental studies validating finite element (FE) predictions of distal radius bone failure load 2 and other strength metrics 3 have evaluated the standard site Unclear if FE predictions acquired from the 4% site accurately predict distal radius failure load 3

4 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 4

5 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 5

6 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 PMMA Edwards & Troy (2012), Medical Engineering & Physics

7 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 PMMA Edwards & Troy (2012), Medical Engineering & Physics

8 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 approach 1 to identify the 4% site Reference line Standard clinical ROI 8 9-block ROI 1. Bonaretti et al (2017), Osteoporosis Int

9 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 approach 1 to identify the 4% site 1. Bonaretti et al (2017), Osteoporosis Int

10 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 approach 1 to identify the 4% site 4% Standard reference line Proximal tip reference line 4% Region 1. Bonaretti et al (2017), Osteoporosis Int

11 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 approach 1 to identify the 4% site 4% 9.5mm Standard reference line Standard Region 1. Bonaretti et al (2017), Osteoporosis Int

12 Methods FE Analysis Employed the single tissue FE model Young s Modulus: GPa 3 Poisson s ratio: 0.3 High-friction axial compression Pistoia s failure criteria 5 Failure load defined as the load leading to 2% of bone tissue exceeding an energy equivalent strain of 7000 µstrain U z y z x 3. MacNeil & Boyd (2008), Bone 5. Pistoia et al (2002), Bone

13 Methods FE Analysis Employed the single tissue FE model 0 mstrain 7000 mstrain Young s Modulus: GPa 3 Poisson s ratio: 0.3 High-friction axial compression Pistoia s failure criteria 4 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

14 4. Edwards & Troy (2012), Medical Engineering & Physics 5. Pistoia et al (2002), Bone 6. Lochmuller et al (2008), JBMR Methods - Experimental Testing Forearms mounted vertically (axial compression) with 0 dorsal inclination and 3-6 radial inclination 6 Compression testing performed at 3mm/s until failure 4,5 Determined ultimate failure load from experimental data 14

15 4. Edwards & Troy (2012), Medical Engineering & Physics 5. Pistoia et al (2002), Bone 6. Lochmuller et al (2008), JBMR Methods - Experimental Testing Forearms mounted vertically (axial compression) with 0 dorsal inclination and 3-6 radial inclination 6 Compression testing performed at 3mm/s until failure 4,5 Determined ultimate failure load from experimental data 15

16 Methods - Experimental Testing 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 16

17 Methods - Statistics Linear regression used to assess relationships between FEderived and experimentally derived failure loads Paired t-test used to compare FE-derived failure load of the standard region and the 4% region 17

18 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)

19 Experimental Failure Load [kn] Experimental Failure Load [kn] Results Standard region and 4% region offered similar predictions of 5 4 distal radius Bone failure failure load (kn) load 5 4 Bone failure load (kn) FE-derived failure load of the standard region and the 4% region did not differ (p = 0.58) 3 Standard VOI 3 4% VOI 2 R² = R² = FE Failure Load [kn] FE Failure Load [kn] 19

20 Discussion 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 20

21 Discussion 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 al Bonaretti et al (2017), Osteoporosis Int

22 Discussion 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 al Bonaretti et al (2017), Osteoporosis Int

23 Discussion Future Research Additional mechanical testing Investigate different modeling approaches and failure criteria Repeat study with off-axis experimental data 23

24 Conclusions 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 24

25 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 25

26 Questions?