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ORIGINAL ARTICLE
Accuracy of patient-specific template-guided vs. free-handfluoroscopically controlled pedicle screw placement in the thoracicand lumbar spine: a randomized cadaveric study
Mazda Farshad1 • Michael Betz1 • Nadja A. Farshad-Amacker2 •
Manuel Moser1
Received: 5 May 2016 / Revised: 1 August 2016 /Accepted: 1 August 2016 / Published online: 9 August 2016
� Springer-Verlag Berlin Heidelberg 2016
Abstract
Purpose Dorsal spinal instrumentation with pedicle screw
constructs is considered the gold standard for numerous
spinal pathologies. Screw misplacement is biomechanically
disadvantageous and may create severe complications. The
aim of this study was to assess the accuracy of patient-
specific template-guided pedicle screw placement in the
thoracic and lumbar spine compared to the free-hand
technique with fluoroscopy.
Methods Patient-specific targeting guides were used for
pedicle screw placement from Th2–L5 in three cadaveric
specimens by three surgeons with different experience
levels. Instrumentation for each side and level was ran-
domized (template-guided vs. free-hand). Accuracy was
assessed by computed tomography (CT), considering per-
forations of\2 mm as acceptable (safe zone). Time effi-
ciency, radiation exposure and dependencies on surgical
experience were compared between the two techniques.
Results 96 screws were inserted with an equal distribution
of 48 screws (50 %) in each group. 58 % (n = 28) of
template-guided (without fluoroscopy) vs. 44 % (n = 21)
of free-hand screws (with fluoroscopy) were fully con-
tained within the pedicle (p = 0.153). 97.9 % (n = 47) of
template-guided vs. 81.3 % (n = 39) of free-hand screws
were within the 2 mm safe zone (p = 0.008). The mean
time for instrumentation per level was 01:14 ± 00:37 for
the template-guided vs. 01:40 ± 00:59 min for the free-
hand technique (p = 0.013), respectively. Increased radi-
ation exposure was highly associated with lesser experi-
ence of the surgeon with the free-hand technique.
Conclusions In a cadaver model, template-guided pedicle
screw placement is faster considering intraoperative
instrumentation time, has a higher accuracy particularly in
the thoracic spine and creates less intraoperative radiation
exposure compared to the free-hand technique.
Keywords Spine surgery � Pedicle screw � Accuracy �Pedicle perforation � Patient-specific
Introduction
Dorsal spinal instrumentation with pedicle screws and rod
constructs has become a widespread surgical procedure in
the treatment of degenerative spinal disease, spinal defor-
mity, trauma and tumors with continuously increasing
numbers [1, 2]. Numerous assistive techniques have been
elaborated over the years harboring advantages and dis-
advantages in terms of screw placement accuracy, radiation
exposure, surgical time, operating room equipment needs,
learning curves and health care costs. Accurate screw
placement can be technically challenging with a demand
for high level spine care centers and surgical expertise.
Screw misplacement not only carries the risk of neuro-
logical or vascular complications, but also has biome-
chanical disadvantages. Patient-specific templates used as
in situ drill guides are an alternative to free-hand or navi-
gated techniques, aiming to improve screw placement
accuracy while at the same time reducing radiation expo-
sure. Originally reported in the late 1990’s by Radermacher
et al. [3], recent advances in computer and additive
& Mazda Farshad
1 Division of Spine Surgery, Balgrist University Hospital
Zurich, Forchstrasse 340, 8008 Zurich, Switzerland
2 Institute of Diagnostic and Interventional Radiology,
University Hospital Zurich, Ramistrasse 101, 8091 Zurich,
Switzerland
123
Eur Spine J (2017) 26:738–749
DOI 10.1007/s00586-016-4728-5
manufacturing technology have led to a more sophisticated
and practical application of template-guided procedures in
spine surgery during the last decade with promising results
[4–13]. We hypothesized that template-guided screw
placement is superior to free-hand placement in terms of
accuracy, radiation exposure and time efficiency. Further,
we hypothesized that surgical experience is less pivotal in
template-guided vs. free-hand pedicle screw placement.
Materials and methods
Three fresh frozen adult cadavers without prior surgery or
deformity of the spine were randomly assigned to three
surgeons with different experience levels, namely two
board-certified orthopedic spine surgeons (chief of spine
surgery and attending spine surgeon at a academic spine
division) and one senior-level neurosurgical resident, all
right-handed. The mean diameter of the pedicles on axial
CT scans at the level Th7 was 4.67 ± 0.85 mm (ranges
3.5–5.5 mm). A randomization list (computerized ran-
domization) was prepared for each cadaver, allocating the
template-guided (MySpine�, Medacta SA International,
Switzerland) and the free-hand technique to the left or right
of each vertebral level (intra-vertebral randomization).
Surgical instrumentation time as well as cumulative radi-
ation dose was recorded. No fluoroscopy was used during
template-guided instrumentation. Time measurement for
the template-guided technique started with the positioning
of the guide onto the vertebra or with the osteotomy to
exhibit the entry point for the free-hand technique. Time
measurement stopped at definitive screw placement. The
diameter of the pedicle screws (MUST�-Medacta Uncon-
strained Screw Technology) ranged from 5 to 6 mm
depending on pre-instrumentation planning on CT and the
screw length ranged from 25 to 55 mm. An illustrative
flow-chart comparing both techniques step-by-step is
shown in Fig. 1.
Presurgical planning, vertebra replica and drill
guide fabrication
According to the manufacturer’s protocol a 0.64 mm
spiral CT scan was performed of each specimen’s spine.
After three-dimensional reconstruction with Mimics�
(Materialise, Leuven, Belgium) a digital surgical plan was
developed including entry point, screw length, screw
diameter, as well as screw angulation in the sagittal,
transversal and coronal plane for each level using Solid-
works� (Dassault Systemes, Velizy-Villacoublay,
France). An illustration of the planning report for one of
the thoracic levels (Th5) is shown in Fig. 2. Planned ‘out
screws’ due to narrow pedicles were marked in the pro-
tocol. The participating surgeons reviewed and validated
the planning. Three-dimensional replicas of all vertebrae
and level-specific drill guides were produced using a rapid
prototyping technique with medical grade polyamide
(P2200) and selective laser sintering (SLS) technology
(P395, EOS e-Manufacturing Solutions, Munich, Ger-
many). The dorsal third of the vertebral replicas including
lamina, spinous process, transverse and articulate pro-
cesses (Fig. 3) allowed the surgeons to check for adequate
contact areas and positioning of the guides prior to
definitive in situ placement.
Surgical technique
A dorsal midline incision was performed at the levels Th1–
L5, including dissection and retraction of the paravertebral
musculature to expose the anatomical bony landmarks,
including the transverse processes. Facet joints and their
respective capsules were fully preserved and the supras-
pinous ligament completely removed. The lamina, spinous
process and transverse processes were depicted as being the
main contact areas for the template (Fig. 3). For this rea-
son, instrumentation was first done with the template-gui-
ded system (Fig. 4) according to the randomization list,
which was blinded to the surgeons until the experiments
started. A K-wire was drilled into the vertebra following
the guide trajectory to a depth consistent with the presur-
gical planning of the desired screw length. With the K-wire
in place the guide was removed and a cannulated drill was
used to burr cortical bone. Finally, predefined cannulated
pedicle screws were inserted over the K-wire. For the free-
hand technique intraoperative fluoroscopy was installed
and the surgeon was free to use it or not for proper screw
placement, depending on how safe he felt with the free-
hand instrumentation. First, an osteotomy was done using
bone rongeurs or a chisel to expose the entry point. The
pedicle was prepared with a Lenke bone probe (Fig. 5) and
a small ball tip was used to check bony integrity of the
pedicle wall. No taps were used. Finally, a screw of the
same diameter and length as planed for the template-guided
technique was inserted free-hand. The level Th1 had to be
excluded from the analysis due to anatomical difficulties
with the specimens and repeated failure to prepare the
pedicles for both techniques.
Postoperative evaluation of pedicle wall integrity
Following instrumentation, a 0.64 mm spiral CT scan of all
cadaveric specimens was performed. An independent
Eur Spine J (2017) 26:738–749 739
123
board certified radiologist, who was blinded to the surgical
technique of screw insertion, reviewed all scans in the
sagittal, transversal and coronal plane on two different
occasions. In cases of disagreement between the two
readouts, the worse grade was used for analysis. Pedicle
wall integrity was classified as normal when the
surrounding cortical bone was fully intact in all three
planes on CT. Perforation was documented whenever the
cortex was harmed or interrupted by any part of the screw,
evident in at least one of the three planes on CT. Perfo-
rations were classified as following: (A) \2 mm,
(B) 2–4 mm or (C) [4 mm (see Fig. 6 for illustrative
Fig. 1 Simplified step-by-step procedures of the free-hand and
template-guided pedicle screw placement technique in the presurgical
phase and during surgery. Dotted lines indicate possible returns to an
earlier stage of the procedure or switching to the free-hand technique
if drill-guide application fails or screw misplacement is suspected
740 Eur Spine J (2017) 26:738–749
123
cases). A perforation of \2 mm was considered accept-
able (safe zone). Additionally, the localization of the per-
foration, if present, was categorized into superior, inferior,
lateral or medial. Possible dependencies on the practical
experience of the surgeons were also evaluated, as well as
individual expenditure of time and cumulative radiation
dose.
Statistical analyses
For the comparison of categorical data Pearson’s Chi-
squared test and Fisher’s exact test were used. A two-tailed
Student’s t test was used for the comparison of means and
descriptive statistics was employed to report means, stan-
dard deviations and ranges. Analysis was performed with
Fig. 2 Three-dimensional planning report for template-guided pedi-
cle screw placement on the level Th5 in one of three cadavers used.
SAR/SAL sagittal plane angle right/left with angulation of the screw
shaft in relation to pedicle center line while center of rotation is
located at the minimal cross section of the pedicle (red dot), TAR/TAL
transversal plane angle right/left with angulation of the screw shaft in
relation to the pedicle center line while center of rotation is located at
the minimal cross section of the pedicle (red dot), HDL/HDR
horizontal distance left/right, VDL/VDR vertical distance left/right
Eur Spine J (2017) 26:738–749 741
123
SPSS Statistics version 23.0 (IBM Corp., Armonk NY,
USA). Results at a probability value p\ 0.05 were con-
sidered statistically significant.
Results
Pedicle perforation rates and grading
96 pedicle screws were inserted with an equal distribution
of 48 screws (50 %) in each group (template-guided vs.
free-hand). 4 screws (Th6 right, Th8 left, Th11 right and L1
right) were repositioned in the free-hand group and 1 screw
(L5 left) in the template-guided group because of suspected
misplacement while operating. Accuracies for each tech-
nique are illustrated in Fig. 7 and categorized in Fig. 8
using the 2 mm cutoff (safe zone).
58.33 % (n = 28) of template-guided screws were fully
contained inside the pedicle, 39.58 % (n = 19) were grade
A and 2.08 % (n = 1) grade B perforations. No grade C
perforation was observed in the template-guided screws.
Lateral perforations were the most frequent ones in this
Fig. 3 Replica of the vertebra Th11 and corresponding drill guide, seen from cranial as labeled on the guide. a Bony contact areas for
appropriate placement of the template. b K-wires inserted on both sides illustrating the screw trajectory and entry points
Fig. 4 Left-sided template-guided screw placement in the upper thoracic spine. a K-wire drilling while ensuring adequate bony contact of the
template. b Use of a cannulated drill to burr cortical bone for widening the entry point. c Screw insertion over the K-wire. d Final screw position
742 Eur Spine J (2017) 26:738–749
123
group with 40 % (n = 8) followed by 35 % (n = 7) medial
perforations, 15 % (n = 3) inferior, 5 % (n = 1) lateral-
inferior and 5 % (n = 1) lateral-medial perforations. All
medial, lateral-inferior and lateral-medial perforations were
grade A. The only grade B perforation was inferior.
43.75 % (n = 21) of the free-hand screws were fully
contained inside the pedicle, 37.5 % (n = 18) were grade
A, 10.42 % (n = 5) grade B and 8.33 % (n = 4) grade C
perforations. Lateral perforations were most frequent in
this group with 81.48 % (n = 22). The remaining 18.52 %
(n = 5) were medial perforations. All medial perforations
were grade A. Grade B and C perforations (n = 9) were
laterally.
Comparison of no perforation vs. any perforation
(grades A–C), in terms of a simple ‘in or out’ method
showed no statistically significant difference depending on
the used surgical technique (p = 0.153). Considering per-
forations of \2 mm as acceptable (safe zone), 97.92 %
(n = 47) of template-guided vs. 81.25 % (n = 39) of free-
hand screws were ‘safe’. A C2 mm breach of the pedicle
cortex was observed in only one pedicle (2.08 %) in the
template-guided group vs. in nine pedicles (18.75 %) in the
free-hand group. Therefore, the selected surgical technique
had a statistically important influence on the severity of
perforation (p = 0.008).
In the thoracic spine, 96.97 % (n = 32) of the template-
guided screws were within and 3.03 % (n = 1, grade B,
Th2 right) outside the safe zone compared to 75.76 %
(n = 25) and 24.24 % (n = 8) of free-hand screws
(p = 0.027), respectively. No significant difference was
seen in the lumbar spine as 100 % (n = 15) of template-
guided and 93.33 % (n = 14) of free-hand screws were
within the safe zone. Only one severe perforation was
observed in the free-hand group (grade C, L1 right) in the
lumbar region.
Surgeon’s experience
Given the \2 mm safe zone, the practical experience of
the surgeons (board-certified vs. senior-level resident) had
no influence on the severity of pedicle perforation with
the free-hand technique (p = 0.697). The limited amount
of severe perforations of the template-guided screws did
not allow analysis in this regard. Likewise, the side of
instrumentation (right vs. left) had no influence on the
severity of pedicle perforation in the free-hand group
(p = 0.137). There was practically no difference in the
template-guided group with 24 left-sided and 23 right-
sided screws within the safe zone and one grade B per-
foration (Th2 right).
Radiation dose and fluoroscopy time
Spiral CT scans for surgical planning had a mean dose
length product (DLP) of 1627.5 ± 71.65 mGy*cm (range
1526.3–1682.4 mGy*cm). It should be noted that, because
of the use of cadavers, these CTs were scanned with a
higher dose [fixed X-ray tube current of 399 mAs instead
of automatic exposure control (AEC)] than would have
been used in living individuals with standard protocols.
Mean intraoperative fluoroscopy dose was 889 ± 604.6
mGycm2 (range 225.1–1687.5 mGycm2) for the free-hand
instrumentation of L5–Th1, and the mean radiation time
was 01:14 ± 00:29 min (range 00:37–01:49 min). Fluo-
roscopy time and cumulative dose showed a negative
correlation with the practical experience of the performing
surgeon (ranges corresponding to the most and least
experienced—see Table 1 for details).
Expenditure of time
Time values for each technique and level are listed for each
cadaver in Table 1. Mean time for template-guided
instrumentation (n = 48) per level was 01:14 ± 00:37 min
(range 00:38–03:58 min) and 01:40 ± 00:59 min (range
00:28–05:48 min) for free-hand instrumentation (n = 48),
the difference being statistically significant (p = 0.013).
Mean total time for template-guided instrumentation of
Th2–L5 was 19:47 ± 04:35 min (range 14:42–25:49 min)
per specimen as compared to 26:40 ± 09:38 min (range
13:21–35:46 min) for the free-hand technique.
Fig. 5 Intraoperative lateral fluoroscopy showing free-hand prepara-
tion of the right pedicle Th5 using a Lenke bone probe with cranial
corresponding to the left side of the picture with template-guided
screws already inserted. The same specimen is also depicted in
Fig. 6c
Eur Spine J (2017) 26:738–749 743
123
Discussion
Screw placement accuracy is based on definition and
assessment with no standardized method or consensus. A
review by Aoude et al. [14] showed that the 2 mm incre-
ment grading, originally proposed in 1990 by Gertzbein
and Robbins [15], is the most commonly used method to
assess pedicle screw accuracy with substantial intra-rater
(j = 0.83) [16] and inter-rater agreement (j = 0.65–0.85)
[16, 17]. Nevertheless, it is a pure radiological grading
system not taking into account possible clinical or biome-
chanical consequences of misplaced pedicle screws, which
are not always necessarily negative (see Fig. 6c).
Parker et al. [18] retrospectively reviewed 6816 free-
hand placed pedicle screws and found a thoracic and
lumbar spine screw accuracy rate of 97.5 and 99.1 %,
respectively. Belmont et al. [19] showed that only 57 % of
279 free-hand placed thoracic pedicle screws in 40 patients
were fully inside the pedicle and 28 % within a 2 mm
breach, the accuracy being the highest in the lower thoracic
spine (Th9–Th12) and lateral breaches occurring signifi-
cantly more often than medial ones (68 vs. 32 %,
p\ 0.005). Similarly, Motiei-Langroudi et al. [20] repor-
ted an overall accuracy rate of 97.7 % for the free-hand
technique with lateral fluoroscopy in 770 thoracolumbar
screws, the accuracy being the highest at the L3–S1 levels
(mean 99 %), followed by the thoracolumbar junction area
(T10–L2, mean 96.5 %) and with the lowest accuracy at
the mid-thoracic area (T7–T9, mean 89.5 %). This is
consistent with our findings that screw placement accuracy
was almost perfect in the lumbar spine for both techniques,
but misplacement was much higher in the thoracic spine for
the free-hand technique. This may be related to several
confounding factors: first, a surgeon’s experience may be
higher for lumbar than thoracic pedicle screw placement.
Second, each surgeon may have his preferred method as
Fig. 6 Axial CT scans illustrating the degrees of perforation. a No
perforation, both L5 screws are fully contained within the pedicle.
b Slight medial wall violation of a left L2 screw (free-hand) being
classified as grade A (\2 mm). c Lateral wall violation of a right Th5
screw (free-hand) being classified as grade B (2–4 mm). d Severe
lateral wall violation of a right Th4 screw (free-hand) being classified
as grade C ([4 mm). Although radiologically classified as severe, this
screw is expected to have strong purchase due to its ‘in-out-in’
trajectory with a tricortical anchorage. Sagittal and coronal planes
were also considered for the evaluation of perforation and are not
depicted here for the ease of illustration
744 Eur Spine J (2017) 26:738–749
123
numerous techniques have been proposed for accurate
screw placement in the thoracic spine [21–24] with
potentially different learning curves. Third, there is a large
inter-segmental variability concerning shape, size and ori-
entation of thoracic pedicles and the relation to adjacent
neural structures [25–27]. The relatively small transversal
diameter of the thoracic pedicles in one specimen may
have contributed to an above-average number of perfora-
tions with both techniques although instrumented by an
experienced surgeon. We observed a greater chance to
misplace pedicle screws laterally, a tendency that has been
reported earlier [19, 25, 28, 29]. This might be due to the
intentional salvage ‘in-out-in technique’ used in narrow
thoracic pedicles to increase biomechanical stability (see
Fig. 6d) and a surgeon’s reasonable fear of neurological
complications in cases of medial wall violations.
Anatomical studies have shown that the distance between
the dural sac and the medial pedicle wall can be within
0.0–0.7 mm in the thoracic spine [30, 31]. Increasing
pedicle screw size in the thoracic spine has been shown to
cause pedicle expansion and breaches laterally without
significantly altering transversal spinal canal diameter in a
cadaveric study [29]. For pedicle screw placement in sin-
gle-level degenerative spondylolisthesis lateral perforations
have also been reported to be more common because of
instability at the instrumented level leading to translation
and rotation of the vertebral body while placing pedicle
screws, a problem that could not be prevented using
intraoperative O-arm navigation for screw placement [32].
In contrary to the well-known learning curves for free-hand
screw placement in thoracic deformity surgery [33–35], no
learning curve was observed for template-guided screws.
In a meta-analysis by Kosmopoulos et al. [36] including
37,337 screws, a median screw accuracy of 86.6 % without
navigation compared to 93.7 % with navigation was
reported for in vivo lumbar and/or thoracic spine surgery,
which was higher than for in vitro studies (79 % without
and 87.3 % with navigation). Mason et al. [37] reviewed 30
articles including 1973 patients and 9310 pedicle screws
and found an accuracy of 68.1 % for free-hand conven-
tional fluoroscopy, 84.3 % for two-dimensional and 95.5 %
for three-dimensional fluoroscopic navigation. Shin et al.
[38] compared fluoroscopically controlled vs. navigation-
guidance coupled with O-arm for screw placement in the
thoracic and lumbosacral spine in a randomized prospec-
tive manner. They found 91.9 % of navigated screws to be
fully contained within the pedicle vs. 87.7 % of fluoro-
scopically placed screws. Tian et al. [39] found median
in vivo screw accuracies of 90.76 % for CT-navigated vs.
85.48 % for two-dimensional fluoroscopy compared to a
higher in vitro median accuracy of 94.59 % for CT-navi-
gated vs. 90.12 % for two-dimensional fluoroscopy. The
reported accuracy of patient-specific template-guided
screws in our study showed a considerably high accuracy
with 97.92 %, which is somehow inferior to the previously
published data with MySpine by Lamartina et al. [13] with
100 % accuracy in 42 screws in a cadaver model. This may
be due to the exclusion of 8/12 perforating screws in the
latter study because the pedicle diameter was considered
too small to avoid perforation, whereas every perforation in
our study was considered for analysis. As for template-
based patient-specific techniques, the accuracy rates for
Fig. 7 Screw placement accuracies for the template-guided and free-
hand technique. Accuracy depicted as no perforation or grade of
pedicle perforation expressed by percentage of screws inserted for
each technique
Fig. 8 Screw placement accuracies for the template-guided and free-
hand technique categorized into no perforation or acceptable perfora-
tions (\2 mm) vs. severe perforations (C2 mm) and expressed by
percentage of screws inserted for each technique. Pearson’s Chi-
squared test revealed that the selected surgical technique had a
statistically important influence on the severity of perforation
(p = 0.008)
Eur Spine J (2017) 26:738–749 745
123
thoracolumbar surgeries given the \2 mm safe zone
have been reported to lie between 96.1 and 100 %
[6–13] and are summarized in Table 2. Lamartina et al.
[13] reported satisfactory results with MySpine target-
ing guides calculating the mean deviation of pedicle
screws between planned and actual screw position in
different planes, with an average deviation from the
planned position at the midpoint of the pedicle of
0.7 mm.
The time needed for unilateral single level preparation
of the pedicle and screw placement was significantly
shorter in the template-guided group, in concordance to a
comparison of computer navigation vs. fluoroscopy in a
review by Meng et al. [40] analyzing 14 articles with 1723
patients and 9019 pedicle screws. It must be critically
stated that this possible reduction of instrumentation time
does not include calculation of the time needed for pre-
operative planning, meticulous soft tissue removal and
adequate bone surface preparation.
Radiation exposure to surgeons and patients during
pedicle screw placement may be unacceptably high using
fluoroscopy [41–43] and largely depends on surgical
experience and the technique used for screw insertion.
Computer assisted image guidance has been shown to
allow a significant reduction in intraoperative radiation
exposure [44], especially when compared to the freehand-
technique [43]. Equally, we could demonstrate that tem-
plate-guided pedicle screw placement potentially allows a
complete reduction of intraoperative fluoroscopy without
sacrificing accuracy, but the definitive need for a presur-
gical CT scan may counterbalances this possible reduction
of radiation exposure.
Table 1 Pure instrumentation time (min) for each level and technique for all three cadavers including surgical experience level, diameter of the
pedicle Th7 on axial CT scan and cumulative fluoroscopy dose and time (see text for details)
Level Senior resident Chief of spine surgery Spine consultant
Pedicle Th 7 on axial CT 5.5 mm Pedicle Th 7 on axial CT 3.5 mm Pedicle Th 7 on axial CT 5.0 mm
Free-
hand
(min)
Template-
guided (min)
Left Right Free-
hand
(min)
Template-
guided (min)
Left Right Free-
hand
(min)
Template-
guided (min)
Left Right
Th2 01:11 02:03 0 0a 01:34 01:07 B Ba 02:22 02:26 0 0a
Th3 01:18 01:26 A Aa 01:09 00:57 A Aa 01:39 01:17 Aa A
Th4 01:02 02:35 0a C 00:52 00:54 B Aa 01:57 02:02 A Aa
Th5 01:22 01:40 0a B 00:55 00:43 Aa A 01:41 01:47 0 Aa
Th6 01:04 01:55 Aa 0 00:53 00:41 Aa A 01:27 04:53 A Aa
Th7 01:10 01:32 A 0a 01:09 00:46 Aa A 01:32 02:44 0a 0
Th8 01:00 02:00 A 0a 01:27 00:50 A 0a 01:11 01:16 Aa C
Th9 01:02 02:45 0 0a 00:51 00:48 Aa B 01:50 01:36 Aa B
Th10 00:53 02:06 0a 0 00:45 00:47 Aa C 01:34 01:06 Aa A
Th11 00:52 02:09 0a 0 00:43 01:09 0 0a 01:13 01:50 0 0a
Th12 00:58 02:07 A Aa 00:39 01:09 0 0a 01:16 02:20 A 0a
L1 00:49 01:30 Aa A 00:41 00:28 0a 0 01:07 05:48 0a C
L2 01:09 02:01 A 0a 00:41 00:35 0a 0 00:58 01:29 0 0a
L3 00:55 01:43 0a 0 00:44 00:46 0 0a 01:04 01:29 0a 0
L4 03:15 01:59 0a A 00:38 00:53 0 0a 01:00 01:21 0a 0
L5 00:51 01:23 0 0a 01:01 00:48 Aa 0 03:58 02:22 A 0a
Mean 01:11 01:56 00:55 00:50 01:37 02:14
SD 00:33 00:22 00:16 00:11 00:43 01:16
Min 00:49 01:23 00:38 00:28 00:58 01:06
Max 03:15 02:45 01:34 01:09 03:58 05:48
Fluoroscopy
dose
(mGycm2)
1687.5 225.1 754.3
Fluroscopy time
(min)
01:49 00:37 01:17
Template-guided screws (left or right) and perforations (0, A, B, C) are highlighted with a superscript letter a
746 Eur Spine J (2017) 26:738–749
123
Limitations of our study are the cadaveric design and
the relatively small sample size, making the assumption
of any of these in vitro data into a clinical context
challenging. The measure of clinical significance of
misplaced pedicle screws is the percentage of symp-
tomatic patients or the need for screw replacement sur-
gery [45], however we can only provide radiological
results. Except for the relative small pedicles in one
specimen, the anatomy found was fairly normal and may
not adequately resembles the anatomy found in an
average spine patient requiring dorsal instrumentation.
Potential drawbacks of the template-guided technique
are: (1) the necessity for meticulous soft tissue removal
including the dorsal ligaments while fully preserving the
bone surface and facet joints, (2) inadequate handling,
e.g. placing the drill template too loose on the bone or
having soft tissue interposed between the guide and the
bone, (3) inadequate digital planning, specifically con-
cerning the quality of the presurgical CT scan with a low
dose protocol and (4) time expenditure for the preoper-
ative planning and production of the drill-guide tem-
plates. Completely resigning intraoperative fluoroscopy
for templated-guided screw placement may not be rec-
ommendable and accuracy should be checked at least at
the end of the procedure or during suspected misplace-
ment while operating. To which extent spinal bone
quality influences the accuracy of template-guided screw
placement and if such a system is useful in (severely)
osteoporotic bone needs to be further investigated,
especially when considering the application of pressure
needed to properly place the template and hold it in firm
contact with the dorsal bony structures.
Conclusions
To our knowledge, this is the first randomized cadaveric
study comparing patient-specific template-guided vs. free-
hand fluoroscopically controlled pedicle screw placement
in the thoracic and lumbar spine using a commercially
available targeting system. The template-guided technique
showed a significantly higher pedicle screw placement
accuracy considering perforations of\2 mm as acceptable,
particularly in the thoracic spine.
Compliance with ethical standards
The study presented here was conducted in accordance with Swiss
and international law requirements. Ethical board’s approval was
obtained from the Ethical Committee of Northwestern and Central
Switzerland with the ID number EKNZ BASEC 2016-00204. The
cadaver workshop was carried out on March 12th 2016 at the
Academy of Medical Training and Simulation (AMTS) in Muttenz,
Switzerland.
Conflict of interest None.
Table 2 Overview of articles describing patient-specific drill templates for pedicle screw placement in the thoracic and lumbar spine including
reported screw placement accuracies
Article Study design Thoracic (T),
lumbar (L), sacral
(S)
Number
of screws
No
perforation
(%)
\2 mm
perforation
(%)
2–4 mm
perforation
(%)
[4 mm
perforation
(%)
Other (%)
Lu et al. [6] Cadaveric ? clinical L 58 58 (100) 0 0 0
Ma et al.
[7]
Cadaveric T 240 224 (93.4) 16 (6.6) 0 0
Lu et al. [8] Clinical T 168 157 (93.45) 11 (6.55) 0 0
Merc et al.
[9]
Clinical L ? S 54 48 (88.89) n.a. n.a. n.a. 6 (11.11)
Sugawara
et al. [10]
Clinical T 58 58 (100) 0 0 0
Lamartina
et al. [13]
Cadaveric T ? L 46 42 (91.3) 4 (8.7) 0 0
Takemoto
et al. [11]
Clinical T (scoliosis) 415 408 (98.4) 1 (0.2) 0
T (OPLL) 46 46 (100) 0 0
Hu et al.
[12]
Clinical T 582 559 (96.05) n.a. n.a. n.a. 23 (3.95)
Current
study
Cadaveric T ? L 48 28 (58.33) 19 (39.58) 1 (2.08) 0
n.a. not available, OPLL ossification of the posterior longitudinal ligament
Eur Spine J (2017) 26:738–749 747
123
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