Posterior spinal fixation based on long spinal rods is the clinical gold standard for the treatment of severe deformities. Rods need to be contoured prior to implantation to fit the natural curvature of the spine. The contouring processes is known to introduce residual stresses and strains which affect the static and fatigue mechanical response of the implant, as determined through time- and cost-consuming experimental tests. Finite element (FE) models promise to provide an immediate understanding on residual stresses and strains within a contoured spinal rods and a further insight on their complex distribution. This study aims at investigating two rod contouring strategies, French bender (FB) contouring (clinical gold standard), and uniform contouring, through validated FE models. A careful characterization of the elastoplastic material response of commercial implants is led. Compared to uniform contouring, FB induces highly localized plasticizations in compression under the contouring pin with extensive lateral sections undergoing tensile residual stresses. The sensitivity analysis highlighted that the assumed postyielding properties significantly affect the numerical predictions; therefore, an accurate material characterization is recommended.

References

References
1.
Luca
,
A.
,
Ottardi
,
C.
,
Sasso
,
M.
,
Prosdocimo
,
L.
,
La Barbera
,
L.
,
Brayda-Bruno
,
M.
,
Galbusera
,
F.
, and
Villa
,
T.
,
2016
, “
Instrumentation Failure Following Pedicle Subtraction Osteotomy: The Role of Rod Material, Diameter, and Multi-Rod Constructs
,”
Eur. Spine J.
,
26
(
3
), pp.
764
770
.
2.
Barton
,
C.
,
Noshchenko
,
A.
,
Patel
,
V.
,
Cain
,
C.
,
Kleck
,
C.
, and
Burger
,
E.
,
2015
, “
Risk Factors for Rod Fracture After Posterior Correction of Adult Spinal Deformity With Osteotomy: A Retrospective Case-Series
,”
Scoliosis
,
10
(
1
), p.
30
.
3.
Smith
,
J. S.
,
Shaffrey
,
E.
,
Klineberg
,
E.
,
Shaffrey
,
C. I.
,
Lafage
,
V.
,
Schwab
,
F. J.
,
Protopsaltis
,
T.
,
Scheer
,
J. K.
,
Mundis
,
G. M.
,
Fu
,
K. M.
,
Gupta
,
M. C.
,
Hostin
,
R.
,
Deviren
,
V.
,
Kebaish
,
K.
,
Hart
,
R.
,
Burton
,
D. C.
,
Line
,
B.
,
Bess
,
S.
, and
Ames
,
C. P.
, and
International Spine Study Group
,
2014
, “
Prospective Multicenter Assessment of Risk Factors for Rod Fracture Following Surgery for Adult Spinal Deformity
,”
J. Neurosurg. Spine
,
21
(
6
), pp.
994
1003
.
4.
Smith
,
J. S.
,
Shaffrey
,
C. I.
,
Ames
,
C. P.
,
Demakakos
,
J.
,
Fu
,
K. M.
,
Keshavarzi
,
S.
,
Li
,
C. M.
,
Deviren
,
V.
,
Schwab
,
F. J.
,
Lafage
,
V.
, and
Bess
,
S.
, and
International Spine Study Group
,
2012
, “
Assessment of Symptomatic Rod Fracture After Posterior Instrumented Fusion for Adult Spinal Deformity
,”
Neurosurgery
,
71
(
4
), pp.
862
867
.
5.
Berjano
,
P.
,
Bassani
,
R.
,
Casero
,
G.
,
Sinigaglia
,
A.
,
Cecchinato
,
R.
, and
Lamartina
,
C.
,
2013
, “
Failures and Revisions in Surgery for Sagittal Imbalance: Analysis of Factors Influencing Failure
,”
Eur. Spine J.
,
22
(
S6
), pp.
853
858
.
6.
Charosky
,
S.
,
Guigui
,
P.
,
Blamoutier
,
A.
,
Roussouly
,
P.
, and
Chopin
,
P.
,
2012
, “
Complications and Risk Factors of Primary Adult Scoliosis Surgery: A Multicenter Study of 306 Patients
,”
Spine
,
37
(
8
), pp.
693
700
.
7.
Yang
,
J. S.
,
Sponseller
,
P. D.
,
Thompson
,
G. H.
,
Akbarnia
,
B. A.
,
Emans
,
J. B.
,
Yazici
,
M.
,
Skaggs
,
D. L.
,
Shah
,
S. A.
,
Salari
,
P.
, and
Poe-Kochert
,
C.
,
2011
, “
Growing Rod Fractures: Risk Factors and Opportunities for Prevention
,”
Spine
,
36
(
20
), pp.
1639
1644
.
8.
La Barbera
,
L.
,
Galbusera
,
F.
,
Wilke
,
H. J.
, and
Villa
,
T.
,
2016
, “
Preclinical Evaluation of Posterior Spine Stabilization Devices: Can the Current Standards Represent Basic Everyday Life Activities?
,”
Eur. Spine J.
,
25
(
9
), pp.
2909
2918
.
9.
La Barbera
,
L.
,
Brayda-Bruno
,
M.
,
Liebsch
,
C.
,
Villa
,
T.
,
Luca
,
A.
,
Galbusera
,
F.
, and
Wilke
,
H. J.
,
2018
, “
Biomechanical Advantages of Supplemental Accessory and Satellite Rods With and Without Interbody Cages Implantation for the Stabilization of Pedicle Subtraction Osteotomy
,”
Eur. Spine J.
(accepted).
10.
Dick
,
J. C.
, and
Bourgeault
,
C.
,
2001
, “
Notch Sensitivity of Titanium Alloy, Commercially Pure Titanium, and Stainless Steel Spinal Implants
,”
Spine
,
26
(
15
), pp.
1668
1672
.
11.
Demura
,
S.
,
Murakami
,
H.
,
Hayashi
,
H.
,
Kato
,
S.
,
Yoshioka
,
K.
,
Yokogawa
,
N.
,
Ishii
,
T.
,
Igarashi
,
T.
,
Fang
,
X.
, and
Tsuchiya
,
H.
,
2015
, “
Influence of Rod Contouring on Rod Strength and Stiffness in Spine Surgery
,”
Orthopedics
,
38
(
6
), pp.
e520
e523
.
12.
Noshchenko
,
A.
,
Xianfeng
,
Y.
,
Armour
,
G. A.
,
Baldini
,
T.
,
Patel
,
V. V.
,
Ayers
,
R.
, and
Burger
,
E.
,
2011
, “
Evaluation of Spinal Instrumentation Rod Bending Characteristics for in-Situ Contouring
,”
J. Biomed. Mater. Res. B: Appl. Biomater.
,
98
(
1
), pp.
192
200
.
13.
Tang
,
J. A.
,
Leasure
,
J. M.
,
Smith
,
J. S.
,
Buckley
,
J. M.
,
Kondrashov
,
D.
, and
Ames
,
C. P.
,
2013
, “
Effect of Severity of Rod Contour on Posterior Rod Failure in the Setting of Lumbar Pedicle Subtraction Osteotomy (PSO): A Biomechanical Study
,”
Neurosurgery
,
72
(
2
), pp.
276
282
.
14.
Slivka
,
M. A.
,
Fan
,
Y. K.
, and
Eck
,
J. C.
,
2013
, “
The Effect of Contouring on Fatigue Strength of Spinal Rods: Is It Okay to Re-Bend and Which Materials Are Best?
,”
Spine Deform.
,
1
(
6
), pp.
395
400
.
15.
Lindsey
,
C.
,
Deviren
,
V.
,
Xu
,
Z.
,
Yeh
,
R. F.
, and
Puttlitz
,
C. M.
,
2006
, “
The Effects of Rod Contouring on Spinal Construct Fatigue Strength
,”
Spine
,
31
(
15
), pp.
1680
1687
.
16.
ASTM,
2016
, “
Standard Test Methods for Tension Testing of Metallic Materials
,” American Society for Testing and Materials, West Conshohocken, PA, Standard No.
ASTM E8/E8M-16a
.http://www.astm.org/cgi-bin/resolver.cgi?E8E8M
17.
Pérez-Pevida
,
E.
,
Brizuela-Velasco
,
A.
,
Chávarri-Prado
,
D.
,
Jiménez-Garrudo
,
A.
,
Sánchez-Lasheras
,
F.
,
Solaberrieta-Méndez
,
E.
,
Diéguez-Pereira
,
M.
,
Fernández-González
,
F. J.
,
Dehesa-Ibarra
,
B.
, and
Monticelli
,
F.
,
2016
, “
Biomechanical Consequences of the Elastic Properties of Dental Implant Alloys on the Supporting Bone: Finite Element Analysis
,”
Biomed. Res. Int.
,
2016
, p. 1850401.
18.
ASTM
,
2014
, “
Standard Specifications and Test Methods for Metallic Angled Orthopedic Fracture Fixation Devices
,” American Society for Testing and Materials, West Conshohocken, PA, Standard No. ASTM F2193-14.
19.
Eberle
,
S.
,
Gerber
,
C.
,
von Oldenburg
,
G.
,
Högel
,
F.
, and
Augat
,
P.
,
2010
, “
A Biomechanical Evaluation of Orthopaedic Implants for Hip Fractures by Finite Element Analysis and In-Vitro Tests
,”
Proc. Inst. Mech. Eng. H
,
224
(
10
), pp.
1141
1152
.
20.
Niinomi
,
M.
,
1998
, “
Mechanical Properties of Biomedical Titanium Alloys
,”
Mater. Sci. Eng. A
,
243
(
1–2
), pp.
231
236
.
21.
Davis
,
J. R.
,
2003
,
Handbook of Materials for Medical Devices
,
ASM International
, Materials Park, OH, p.
41
.
22.
Mirone
,
G.
,
Barbagallo
,
R.
,
Corallo
,
D.
, and
Di Bella
,
S.
,
2016
, “
Static and Dynamic Response of Titanium Alloy Produced by Electron Beam Melting
,”
Procedia Struct. Integr.
,
2
, pp.
2355
2366
.
23.
ASTM,
2013
, “
Standard Specification for Wrought Titanium-6Aluminum-4Vanadium ELI (Extra Low Interstitial) Alloy for Surgical Implant Applications (UNS R56401)
,” American Society for Testing and Materials, West Conshohocken, PA, Standard No.
ASTM F136-13
.http://www.astm.org/cgi-bin/resolver.cgi?F136
24.
Melkerson
,
M. N.
,
Griffith
,
S. L.
, and
Kirkpatrick
,
J. S.
,
2003
, “
Spinal Implants: Are We Evaluating Them Appropriately?
,” ASTM International, West Conshohocken, PA, Standard No.
ASTM STP1431-EB
.https://www.astm.org/DIGITAL_LIBRARY/STP/SOURCE_PAGES/STP1431.htm
25.
Nguyen
,
T. Q.
,
Buckley
,
J. M.
,
Ames
,
C.
, and
Deviren
,
V.
,
2011
, “
The Fatigue Life of Contoured Cobalt Chrome Posterior Spinal Fusion Rods
,”
Proc. Inst. Mech. Eng. H
,
225
(
2
), pp.
194
198
.
26.
Oberwinkler
,
B.
,
2016
, “
On the Anomalous Mean Stress Sensitivity of Ti-6Al-4V and Its Consideration in High Cycle Fatigue Lifetime Analysis
,”
Int. J. Fatigue
,
92
, pp.
368
381
.
27.
Takakuwa
,
O.
,
Nakai
,
M.
,
Narita
,
K.
,
Niinomi
,
M.
,
Hasegawa
,
K.
, and
Soyama
,
H.
,
2016
, “
Enhancing the Durability of Spinal Implant Fixture Applications Made of Ti–6Al–4V ELI by Means of Cavitation Peening
,”
Int. J. Fatigue
,
92
, pp.
360
367
.
You do not currently have access to this content.