This document discusses meshing the human lumbar spine for finite element analysis (FEA). It describes how CT scan data was used to generate 3D models of vertebrae in the lumbar spine. Each vertebra was then meshed using techniques like circular lines, shell elements, and solid mapping to create a hybrid mesh. The meshed vertebrae were then connected together along with intervertebral discs. Loads applied to the neck and pelvis allowed large displacement simulation to predict deformation and stresses. An implant was introduced between discs in the FEA model to study stresses before and after a surgical procedure. The meshing techniques allowed NuVasive to use FEA to analyze the human lumbar spine.

1. Meshing the Human Lumbar Spine
2015 Americas Altair Technology Conference
May 5-7, 2015
Jeff Harris
Sundar Gopalan

2. ABOUT NUVASIVE®
#3 in the global spine industry
A pure play
spine company
Specializing in minimally
disruptive surgical procedures
Driving the shift toward minimally
invasive spine surgery
Pioneered lateral access spine
surgery with eXtreme Lateral
Interbody Fusion (XLIF®)
NuVasive, Inc.

3. ABOUT NUVASIVE®
The NuVasive® approach to
Minimally Invasive Surgery (MIS) is
a surgical platform considered to be
Maximum Access Surgery (MAS®).
MAS procedures deliver the benefits
of less invasive surgery through safe
and reproducible techniques.
HISTORY OF
EXPLOSIVE
GROWTH
REVENUE IN MILLIONS
Source: NuVasive Company Financial
Statements
• From start-up to #3 in the U.S. Spine Industry in less
than 10 years
• Growth fueled by innovation and by the shift
from traditional to MAS/MIS spine procedures
$12 $23 $38 $63
$98
$154
$250
$370
$478
$540
$620
$685
2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013

4. SPEED OF INNOVATION
Source: Idata Research Inc.
All percentages are estimates.
NUVASIVE® IS
DRIVING THE SHIFT
TOWARD MINIMALLY
DISRUPTIVE SURGERY
Within 10 years, MAS/MIS procedures are
expected to represent 80% of all spine surgeries.
Others
23%
Medtronic
24%
NuVasive
19%Depuy Synthes
18%
Stryker
8%
Zimmer
4%
Globus
4%
Minimally Invasive Spinal
Implant Market in 2012

5. NuVasive® offers more than
90 products in its portfolio.
Our products have been
used in tens of thousands
of cases worldwide.
®
Affix®
2008
ABOUT NUVASIVE

6. • Biomechanical functions of the spine
– Transfer weight & bending moments
from the head, trunk, and external loads
to the pelvis
– Allow physiologic motion between head,
trunk, and pelvis
– Protect the spinal cord
INTRODUCTION

7. • Complex geometry requires a robust meshing tool.
LUMBAR SPINE ANATOMY
Spinous Process
Vertebral Body
Transverse Process
Superior Facet
Inferior Facet
Pedicle
Interior
Region
Posterior
Region

8. • Cadaveric testing typically performed to evaluate the biomechanics of
medical devices in a more clinically relevant setting.
• FEA offers significant advantages in repeatability and direct
comparison
• Simulate cadaveric testing with a computer model:
– Eliminates specimen variability.
– Less cost/time (once base model is created).
– Can evaluate multiple designs under the same anatomical and
biomechanical conditions.
• Stress analysis of bone, soft tissue and implants.
• Requires complex anatomical model + complex anisotropic, non-linear
materials.
FEA IN BIOMECHANICS

9. REGULATORY APPLICATIONS

10. • Anatomic geometry obtained using thresholded CT
Segmentation
– CT scan produces “virtual slices” from many different
angles
– Slices can be stacked together to create a 3D rendering.
• Mesh generation
• Apply appropriate material models
GEOMETRY

11. 1. Import STL and partition the vertebral
body elements away from the
posterior elements.
2. Create circular line and circular
mesh.
3. Create shell elements inside line and
morph to create oblong shape to
capture the body profile.
METHODS

12. 4. Duplicate morph those shells to
the top and bottom surfaces of
the vertebral body.
5. Solid Map mesh between the
shells to create the core solid
elements.
6. Create faces (i.e. shells) to create
elements around solid elements
METHODS

13. 7. Then duplicate morph those shells
outward to the original body
geometry
8. Solid Map mesh between those
transverse shells
9. Using same Solid Map technique,
solid mesh around the remaining top
and bottom areas
METHODS

14. 10.Connect the shell elements to the body and tetramesh using node
merging. This will create a volume that can be meshed and create the
hybrid meshed vertebrae
METHODS

15. 12.Use same process to mesh the other vertebrae.
13.Connect the vertebrae by solid map meshing
between the faces defining the intervertebral
discs
METHODS

16. 14.Use morphing to add any needed shaping
METHODS

17. • HyperMesh was critical in meshing the complex STL file and Moments
from the neck and pelvis were applied to the meshed model
• Large Displacement simulation was carried out to predict the
deformation and stress in the test experiment before the surgical
procedure
• To the existing FEA model an implant was introduced between the
discs with the corresponding material and properties
• This study helped NuVasive predict stresses induced in the Human
Lumbar Spine before and after the surgical procedure
CONCLUSION

18. • Jeff Harris – Senior Engineer, Computational Biomechanics
NuVasive, Inc.
7475 Lusk Blvd. San Diego, CA 92121
jharris@nuvasive.com
(858)909-1939
CONTACT

19. NuVasive, Inc. 7475 Lusk Blvd., San Diego, CA 92121 • phone: 800-475-9131 fax: 800-475-9134
NuVasive UK Ltd. Ste. B, Ground Floor, Caspian House, The Waterfront, Elstree, Herts WD6 3BS UK
phone: +44 (0) 208-238-7850 fax: +44 (0) 207-998-7818
www.nuvasive.com
© 2013. NuVasive, Inc. All rights reserved. , , NuVasive, Speed of Innovation, ILIF, MAS, NVJJB, NVM5,
PCM, SOLAS, The Better Way Back, and XLIF are registered trademarks of NuVasive, inc. NuVasive Spine
Foundation is a common law trademark of NuVasive, Inc. 13-NUVA-451