Examine the biomechanical effect of material properties, geometric variables, and anchoring arrangements in a segmental pedicle screw with connecting rods spanning the entire lumbar spine using finite element models (FEMs). The objectives of this study are (1) to understand how different variables associated with posterior instrumentation affect the lumbar spine kinematics and stresses in instrumentation, (2) to compare the multidirectional stability of the spinal instrumentation, and (3) to determine how these variables contribute to the rigidity of the long-segment fusion in a lumbar spine. A lumbar spine FEM was used to analyze the biomechanical effects of different materials used for spinal rods (TNTZ or Ti or CoCr), varying diameters of the screws and rods (5 mm and 6 mm), and different fixation techniques (multilevel or intermittent). The results based on the range of motion and stress distribution in the rods and screws revealed that differences in properties and variations in geometry of the screw-rod moderately affect the biomechanics of the spine. Further, the spinal screw-rod system was least stable under the lateral bending mode. Stress analyzes of the screws and rods revealed that the caudal section of the posterior spinal instrumentation was more susceptible to high stresses and hence possible failure. Although CoCr screws and rods provided the greatest spinal stabilization, these constructs were susceptible to fatigue failure. The findings of the present study suggest that a posterior instrumentation system with a 5-mm screw-rod diameter made of Ti or TNTZ is advantageous over CoCr instrumentation system.

References

References
1.
Panjabi
,
M. M.
,
1988
, “
Biomechanical Evaluation of Spinal Fixation Devices—I: A Conceptual Framework
,”
Spine
,
13
(
10
), pp.
1129
1134
.
2.
Ambati
,
D. V.
,
Wright
,
E. K.
, Jr.
,
Lehman
,
R. A.
, Jr
,
Kang, D. G.
,
Wagner, S. C.
, and
Dmitriev, A. E.
,
2015
, “
Bilateral Pedicle Screw Fixation Provides Superior Biomechanical Stability in Transforaminal Lumbar Interbody Fusion: A Finite Element Study
,”
Spine J.
,
15
(
8
), pp.
1812
1822
.
3.
Gong
,
Z.
,
Chen
,
Z.
,
Feng
,
Z.
,
Cao, Y.
,
Jiang, C.
, and
Jiang, X.
,
2014
, “
Finite Element Analysis of 3 Posterior Fixation Techniques in the Lumbar Spine
,”
Orthopedics
,
37
(
5
), pp.
e441
e448
.
4.
Galbusera
,
F.
,
Bassani
,
T.
,
La Barbera
,
L.
,
Ottardi, C.
,
Schlager, B.
,
Brayda-Bruno, M.
,
Villa, T.
, and
Wilke, H. J.
,
2015
, “
Planning the Surgical Correction of Spinal deformities: Toward the Identification of the Biomechanical Principals by Means of Numerical Simulation
,”
Front Bioeng. Biotechnol.
,
3
, p.
178
.
5.
Rohlmann
,
A.
,
Burra
,
N. K.
,
Zander
,
T.
, and
Bergmann, G.
,
2007
, “
Comparison of the Effects of Bilateral Posterior Dynamic and Rigid Fixation Devices on the Loads in the Lumbar Spine: A Finite Element Analysis
,”
Eur. Spine J.
,
16
(
8
), pp.
1223
1231
.
6.
Facchinello
,
Y.
,
Brailovski
,
V.
, and
Petit
,
Y.
,
2014
, “
Monolithic Superelastic Rods With Variable Flexural Stiffness for Spinal Fusion: Simplified Finite Element Analysis of an Instrumented Spine Segment
,” 36th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (
EMBC
), Chicago, IL, Aug. 26--30, pp.
6605
6608
.
7.
Charosky
,
S.
,
Moreno
,
P.
, and
Maxy
,
P.
,
2014
, “
Instability and Instrumentation Failures After a PSO: A Finite Element Analysis
,”
Eur. Spine J.
,
23
(
11
), pp.
2340
2349
.
8.
Cunningham
,
B. W.
,
Sefter
,
J. C.
,
Shono
,
Y.
, and
McAfee, P. C.
,
1993
, “
Static and Cyclical Biomechanical Analysis of Pedicle Screw Spinal Constructs
,”
Spine
,
18
(
12
), pp.
1677
1688
.
9.
Chen
,
P. Q.
,
Lin
,
S. J.
,
Wu
,
S. S.
, and
So, H.
,
2003
, “
Mechanical Performance of the New Posterior Spinal Implant: Effect of Materials, Connecting Plate and Pedicle Screw Design
,”
Spine
,
28
(
9
), pp.
881
886
.
10.
Pienkowski
,
D.
,
Stephens
,
G. C.
,
Doers
,
T. M.
, and
Hamilton, D. M.
,
1998
, “
Multicycle Mechanical Performance of Titanium and Stainless Steel Transpedicular Spine Implants
,”
Spine
,
23
(
7
), pp.
782
788
.
11.
Metzger
,
M. F.
,
Robinson
,
S. T.
,
Svet
,
M. T.
,
Liu, J. C.
, and
Acosta, F. L.
,
2016
, “
Biomechanical Analysis of the Proximal Adjacent Segment After Multilevel Instrumentation of the Thoracic Spine: Do Hooks Ease the Transition?
,”
Global Spine J.
,
6
(
4
), pp.
335
343
.
12.
Facchinello
,
Y.
,
Brailovski
,
V.
,
Petit
,
Y.
,
Brummund, M.
,
Tremblay, J.
, and
Mac-Thiong, J. M.
,
2015
, “
Biomechanical Assessment of the Stabilization Capacity of Monolithic Spinal Rods With Different Flexural Stiffness and Anchoring Arrangement
,”
Clin. Biomech. (Bristol, Avon)
,
30
(
10
), pp.
1026
1035
.
13.
Han
,
S.
,
Hyun
,
S. J.
,
Kim, K. J.
,
Jahng, T. A.
,
Lee, S.
, and
Rhim, S. C.
,
2017
, “
Rod Stiffness as a Risk Factor of Proximal Junctional Kyphosis After Adult Spinal Deformity Surgery: Comparative Study Between Cobalt Chrome Multiple-Rod Constructs and Titanium Alloy Two-Rod Construct
,”
Spine J.
,
17
(
7
), pp.
962
968
.
14.
Ashman
,
R. B.
,
Birch
,
J. G.
,
Bone
,
L. B.
,
Corin, J. D.
,
Herring, J. A.
,
Johnston, C. E., II
,
Ritterbush, J. F.
, and
Roach, J. W.
,
1988
, “
Mechanical Testing of Spinal Instrumentation
,”
Clin. Orthop. Relat. Res.
,
227
, pp.
113
125
.
15.
Ruberte
,
L. M.
,
Natarajan
,
R. N.
, and
Andersson
,
G. B.
,
2009
, “
Influence of Single-Level Lumbar Degenerative Disc Disease on the Behavior of the Adjacent Segments—A Finite Element Study
,”
J. Biomech.
,
42
(
3
), pp.
341
348
.
16.
Natarajan
,
R. N.
, and
Andersson
,
G. B.
,
2016
, “
Lumbar Disc Degeneration is an Equally Important Risk Factor as Lumbar Fusion for Causing Adjacent Segment Disc Disease
,”
J. Orthop. Res.
,
35
(1), pp. 123–130.
17.
Qasim
,
M.
,
Hong
,
J. T.
,
Natarajan
,
R. N.
, and
An, H. S.
,
2013
, “
A Biomechanical Comparison of Intralaminar C7 Screw Constructs With and Without Offset Connector Used for C6-7 Cervical Spine Immobilization: A Finite Element Study
,”
J. Korean Neurosurg. Soc.
,
53
(
6
), pp.
331
336
.
18.
Natarajan
,
R. N.
,
Williams
,
J. R.
, and
Andersson
,
G. B.
,
2006
, “
Modeling Changes in Intervertebral Disc Mechanics With Degeneration
,”
J. Bone Jt. Surg. Am.
,
88
(Suppl. 2), pp.
36
40
.https://www.researchgate.net/publication/7185215_Modeling_changes_in_intervertebral_disc_mechanics_with_degeneration
19.
Williams
,
J. R.
,
Natarajan
,
R. N.
, and
Andersson
,
G. B.
,
2007
, “
Inclusion of Regional Poroelastic Material Properties Better Predicts Biomechanical Behavior of Lumbar Disc Subjected to Dynamic Loading
,”
J. Biomech.
,
40
(
9
), pp.
1981
1987
.
20.
Niinomi
,
M.
,
2007
, “
Fatigue Characteristics of Metallic Biomaterials
,”
Int. J. Fatigue
,
29
(
6
), pp.
992
1000
.
21.
Weinstein
,
J. N.
,
Spratt
,
K. F.
,
Spengler
,
D.
,
Brick, C.
, and
Reid, S.
,
1988
, “
Spinal Pedicle Fixation: Reliability and Validity of Roentgenogram-Based Assessment and Surgical Factors on Successful Screw Placement
,”
Spine
,
13
(
9
), pp.
1012
1018
.
22.
Rohlmann
,
A.
,
Bergmann
,
G.
, and
Graichen
,
F.
,
1997
, “
Loads on an Internal Spinal Fixation Device During Walking
,”
J. Biomech.
,
30
(
1
), pp.
41
47
.
23.
Renner
,
S. M.
,
Natarajan
,
R. N.
,
Patwardhan
,
A. G.
,
Havey, R. M.
,
Voronov, L. I.
,
Guo, B. Y.
,
Andersson, G. B.
, and
An, H. S.
,
2007
, “
Novel Model to Analyze the Effect of a Large Compressive Follower Pre-Load on Range of Motions in a Lumbar Spine
,”
J. Biomech.
,
40
(
6
), pp.
1326
1332
.
24.
Li
,
G.
,
Wang
,
S.
,
Passias
,
P.
,
Xia, Q.
,
Li, G.
, and
Wood, K.
,
2009
, “
Segmental In Vivo Vertebral Motion During Functional Human Lumbar Spine Activities
,”
Eur. Spine J.
,
18
(
7
), pp.
1013
1021
.
25.
Passiac
,
P. G.
,
Wang
,
S.
,
Kozanek
,
M.
,
Xia, Q.
,
Li, W.
,
Grottkau, B.
,
Wood, K. B.
, and
Li, G.
,
2011
, “
Segmental Lumbar Rotation in Patients With Discogenic Low Back Pain During Functional Weight-Bearing Activities
,”
J. Bone Jt. Surg. Am.
,
93
(
1
), pp.
29
37
.
26.
Jutte
,
P. C.
, and
Castelein
,
R. M.
,
2002
, “
Complications of Pedicle Screws in Lumbar and Lumbosacral Fusions in 105 Consecutive Primary Operations
,”
Eur. Spine J.
,
11
(
6
), pp.
594
598
.
27.
Pihlajamaki
,
H.
,
Myllynen
,
P.
, and
Bostman
,
O.
,
1997
, “
Complications of Transpedicular Lumbosacral Fixation for Non-Traumatic Disorders
,”
J. Bone Jt. Surg. Br.
,
79
(
2
), pp.
183
189
.
28.
Farrokhi
,
M. R.
,
Razmkon
,
A.
,
Maghami, Z.
, and
Nikoo, Z.
,
2010
, “
Inclusion of the Fracture Level in Short Segment Fixation of Thoracolumbar Fractures
,”
Eur. Spine J.
,
19
(
10
), pp.
1651
1656
.
29.
Chen
,
C. S.
,
Chen
,
W. J.
,
Cheng, C. K.
,
Jao, S. H.
,
Chueh, S. C.
, and
Wang, C. C.
,
2005
, “
Failure Analysis of Broken Pedicle Screws on Spinal Instrumentation
,”
Med. Eng. Phys.
,
27
(
6
), pp.
487
496
.
30.
Kwon
,
B. K.
,
Elgafy
,
H.
,
Keynan, O.
,
Fisher, C. G.
,
Boyd, M. C.
,
Paquette, S. J.
, and
Dvorak, M. F.
,
2006
, “
Progressive Junctional Kyphosis at the Caudal End of Lumbar Instrumented Fusion: Etiology, Predictors, and Treatment
,”
Spine
,
31
(
17
), pp.
1943
1951
.
You do not currently have access to this content.