Neurospine
Neurospine 2023;20(1):308-316.
https://doi.org/10.14245/ns.2244888.444
Original Article
Corresponding Author
Tsung-Hsi Tu
https://orcid.org/0000-0002-0550-5855
Department of Neurosurgery, Neurological
Institute, Taipei Veterans General Hospital,
Room 525, 17F, No. 201, Shih-Pai Road,
Sec. 2, Beitou, Taipei 11217, Taiwan
Email: thtu0001@gmail.com
Received: October 14, 2022
Revised: December 15, 2022
Accepted: December 20, 2022
This is an Open Access article distributed under
the terms of the Creative Commons Attribution
Non-Commercial License (https://creativecommons.org/licenses/by-nc/4.0/) which permits
unrestricted non-commercial use, distribution,
and reproduction in any medium, provided the
original work is properly cited.
Copyright © 2023 by the Korean Spinal
Neurosurgery Society
pISSN 2586-6583 eISSN 2586-6591
Comparison of Cortical Bone
Trajectory to Pedicle-Based Dynamic
Stabilization: An Analysis of 291
Patients
Chih-Chang Chang1,2,3, Hsuan-Kan Chang1,2, Chin-Chu Ko1,2, Ching-Lan Wu1,2,4,
Yi-Hsuan Kuo1,2, Tsung-Hsi Tu1,2, Wen-Cheng Huang1,2, Jau-Ching Wu1,2
Department of Neurosurgery, Neurological Institute, Taipei Veterans General Hospital, Taipei, Taiwan
School of Medicine, National Yang-Ming Chiao-Tung University, Taipei, Taiwan
3
Department of BioMedical Engineering, National Yang-Ming Chiao-Tung University, Taipei, Taiwan
4
Department of Radiology, Taipei Veterans General Hospital, Taipei, Taiwan
1
2
Objective: Pedicle-based dynamic stabilization (DS) has gained popularity outside of America. Although pedicle screw (PS) loosening has always been a concern, it is reportedly innocuous. Cortical bone trajectory (CBT) screw is an emerging option with less invasiveness
and similar effectiveness to PS in short-segment lumbar fusion. This study aimed to verify
the use of CBT for DS by comparing the outcomes between pedicle- and CBT-based DS.
Methods: Consecutive patients with lumbar spondylosis or low-grade spondylolisthesis
who underwent 1- or 2-level DS between L3–5 with a minimum follow-up of 24 months
were reviewed. Screw loosening was determined by computed tomography and the incidences were compared.
Results: A total of 291 patients who underwent Dynesys DS (235 pedicle- and 56 CBT-based,
respectively) were compared. The demographics and preoperative conditions were similar.
All the clinical outcomes improved at 24-month postoperation, while the CBT-based group
had less operation time and blood loss than the pedicle-based group. The rates of screw
loosening were lower in the CBT-based (5.4% per screw and 12.5% per patient) than the
pedicle-based group (9% per screw and 26.4% per patient). Furthermore, there were no
differences in the clinical outcomes and complication profiles.
Conclusion: The CBT-based DS for 1- or 2-level lumbar degeneration demonstrated equivalent clinical improvement as the pedicle-based DS. The adaption of CBT-based screws for
DS could be a less invasive approach (shorter operation time and less blood loss), with lower chances of screw loosening than the conventional PS-based DS.
Keywords: Pedicle screw-based, Dynamic stabilization, Screw loosening, Cortical bone
trajectory
INTRODUCTION
Although lumbar fusion remains a standard surgical option
for instability caused by spondylosis or spondylolisthesis, spinal
arthrodesis inevitably would raise the concern of decreased
segmental mobility and subsequent risks of adjacent segment
disease (ASD). Therefore, there has been the emerging technology of dynamic stabilization (DS) as an alternative management,
308 www.e-neurospine.org
which has aimed at preservation of the segmental motion and
mitigation of the risks of ASD.1-15 In the past decade, reports
have demonstrated satisfactory outcomes, including clinical
improvements, low complication rates, and potential of motion
preservation in the management of lumbar degenerative diseases of short-segments.5,7,9,16,17 However, there are also adverse
events reported with DS, including pedicle screw (PS) loosening and unintended facet arthrodesis.18-21
Chang CC, et al.
Cortical Bone Trajectory Dynamic Stabilization
In the nonfusion construct of DS, which theoretically under
long-term and repeated mechanical load, the PS reasonably
may be subject to loosening or fatigue at the metal-to-bone interface.22 In the literature regarding DS, the reported incidences
of PS loosening varied among the series, ranging from 7% to
20%.1,2,5,7-11,13,16,23,24 Interestingly, the PS loosening of DS is usually associated with little adverse clinical outcomes, and some of
the recent series have attributed this to the unintended facet fusion after DS.18,19,21 Furthermore, it is unclear whether the dynamic motility of lumbar segments after instrumentation is maintained for long or they are fused slowly.19,21
The recent innovation of cortical bone trajectory (CBT) screws,
first reported in 2009 as an alternative to traditional PS,25,26 assume a medial-to-lateral and caudal-to-cephalad direction to
engage the dense cortical bone of pars interarticularis, pedicle,
and lateral wall of the vertebrae (Fig. 1). The adaption of CBT
has demonstrated feasibility and effectiveness in short-segment
lumbar fusion surgery.25,27-29 According to biomechanical studies, the CBT had up to a 30% increase of pullout strength compared to the conventional pedicle trajectory.26,30 Since CBT potentially improves bone-to-screw osteointegration and reinforces the screw purchase to decrease screw loosening or breakage,
it might be a reasonable innovation to adapt CBT for DS in the
management of lumbar instability.31 Moreover, CBT screws re-
quire less muscle dissection than the conventional PS, because
the medial-to-lateral directions of CBT spare the need for exposure of the transverse-process-facet junction. Less extensive
dissection of the soft tissues for CBT may also merit the rationale of motion preservation in DS. The authors have previously
reported the safety and feasibility of CBT-based DS.31
In this study, an attempt was made to compare the innovative
CBT-based DS to standard pedicle-based DS. Clinical and radiological evaluations, including screw loosening, over more
than 2 years of follow-up are demonstrated.
MATERIALS AND METHODS
1. Study Design and Patient Inclusion
This was a single center, retrospective comparison study that
included consecutive patients with degenerative disease between
L3 to L5 who underwent DS. The DS was indicated in patients
who had degenerative spondylosis included symptomatic lumbar spinal stenosis without instability, recurrent disc herniation
with or without previous discectomy, degenerative disc disease
with discogenic pain, intractable radicular pain, back pain, or
neurologic claudication that were refractory to conservative treatment for more than 4 months. The DS was also indicated in
patients who had spondylolisthesis no more than Meyerding
grade I (percentage of vertebrae slip between 0% to 25%). Exclusion criteria were patients who did not complete the 24-month
follow-up, had involved levels of disease other than at L3-4-5,
spondylolisthesis more than Meyerding grade I, lytic spondylolisthesis, or thoracolumbar deformity indicated by screening
standing radiographs. All methods were carried out in accordance with STROBE (Strengthening the Reporting of Observational Studies in Epidemiology) guidelines and regulations. The
study protocol had been approved by the Institutional Review
Board (IRB) of Taipei Veterans General Hospital (IRB No. 201912-001AC) and informed consent from each patient was obtained.
All patients used the same system of instrumentation, Dynesys DS (Zimmer Biomet, Warsaw, IN, USA) featured with screws,
polycarbonate urethan spacers, and polyester cords to achieve
DS. Since mid-2017, all patients who underwent DS adopted
the CBT screws in the authors’ service and were compared to
previous patients who used the PS in DS. Thus, patients were
grouped into two: the PS-based and the CBT-based groups by
the timing of surgery. All the perioperative management and
follow-ups were constant in the series.
Fig. 1. Comparison of cortical bone trajectory and pedicle
trajectory.
https://doi.org/10.14245/ns.2244888.444
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309
Chang CC, et al.
Cortical Bone Trajectory Dynamic Stabilization
2. Surgical Technique
1) Decompression
After general anesthesia, patients were put in a prone position on the Wilson frame with neutral lumbar lordosis. A midline incision was made and deepened for subperiosteal muscular dissection. The lamina was removed as well as the thickened
ligamentum flavum. The medial part of the facet joints was removed up to the pedicles to decompress the lateral recess. If
needed, foraminotomy was performed by removing bone spur
and flavum ligament with curette and Kerrison rongeur to enlarge the foramen. Nerve roots were palpated along the exiting
path with a Woodson dissector to ensure adequate decompression of the neuroforamen. Typically, the surgery required no
discectomy since the lateral recesses were always decompressed
thoroughly. However, removal of sequestrated disc fragments
was performed on those patients who had ruptured intervertebral discs. Care was taken to avoid violation of the facets more
than the medial-third.
dures.3,4,12,20 (Fig. 2. Please see https://sketchfab.com/TaroYen/
models for interactive 3-dimensional images and an enhanced
version of Fig. 2).
3) CBT-based DS
The entry points of the CBT screws were generally over the
cephalad lateral part of the pars interarticularis, slightly caudal
to the sulcus of the facet complex. A high-speed drill was used
to break through the cortex. The trajectory was confirmed by
intraoperative fluoroscopy, which allowed the screw to course
through the dense cortical bone with the screw tip barely penetrating the cortex of the vertebral body laterally. According to
biomechanical studies, the proper size of CBT screws was 5.0 to
5.5 mm in diameter and 35 to 40 mm in length.32 Therefore, the
most commonly used screws were 5.2 mm × 35 mm in CBTbased DS. A 5.2-mm cannulated tap was used to create the screw
tract. The Dynesys screws were subsequently placed. The polycarbonate urethan spacer and polyethylene-terephthalate cord
were subsequently assembled31 (Fig. 2).
2) Pedicle-based DS
From the midline wound, bilateral fascia dissections were
then made for entering the intermuscular plane (Wiltse plane)
under the guidance of intraoperative fluoroscopy. The Dynesys
screws were placed in a transpedicular trajectory via the insertion point at the base of the transverse process without additional facet destruction. The length and diameter of the screws
were determined by preoperative computed tomography (CT)
scans and confirmed intraoperatively. The diameter of the most
commonly used screws in pedicle-based DS was 6.4 mm. The
polycarbonate urethan spacers were tailored for only slight distraction of the facet joints. The spacers were then inserted together with the polyester cord, following the standard proce-
A
B
Fig. 2. Illustration of cortical bone trajectory (A) and pediclebased dynamic stabilization (B). Copyright Shao-Yen Huang.
Published with permission. Please see https://sketchfab.com/
TaroYen/models for interactive 3-dimensional images and an
enhanced version of Fig. 2.
310 www.e-neurospine.org
4) Clinical evaluation
The clinical data were prospectively collected and retrospectively reviewed. Clinical outcomes, including visual analogue
scale (VAS) for back and leg pain and the Oswestry Disability
Index (ODI) scores, were assessed pre-operatively and at 6 weeks
and at 3, 6, 12, 18, and 24 months postoperatively.
5) Radiographical evaluation
Every patient underwent preoperative lumbar images, including anteroposterior and lateral radiography, lateral dynamic
radiography, magnetic resonance imaging and CT scans. Fol-
A
B
Fig. 3. Radiographs of (A) a 73-year-old male who underwent
Pedicle-based dynamic stabilization at L3-4-5, (B) a 68-yearold female who underwent cortical bone trajectory dynamic
stabilization at L3-4-5. Loosened screws are documented (arrowhead).
https://doi.org/10.14245/ns.2244888.444
Chang CC, et al.
Cortical Bone Trajectory Dynamic Stabilization
56 patients underwent CBT-based DS. The mean age was
61.7 ± 10.9 versus 62.5 ± 10.4, p = 0.61. There were 117 male patients (49.7%) in the pedicle-based group compared to 27 (48.2%)
in the CBT-based group (p = 0.83). Medical comorbidities were
similar between the 2 groups, as the incidence rates of hypertension and diabetes mellitus were similar (42.6% vs. 37.5% and
21.7% vs. 16.1%, p = 0.49 and 0.35, respectively) in both groups.
There was no difference in the body mass index (BMI) between
the 2 groups (25.8± 3.8 kg/m2 vs. 25.7± 2.4 kg/m2, p= 0.92). The
pathologies and distribution of levels were also similar in both
groups (p= 0.82 and 0.87, respectively). The pedicle-based group
had an average longer follow-up than the CBT-based group
(61.8 ± 34.9 months vs. 31.2 ± 6.1 months, p < 0.001) (Table 1).
low-up images included standard anteroposterior, lateral and
flexion-extension radiography immediately postoperative, and
at 6 weeks, and at 3, 6, 12, 18, and 24 months after surgery. An
initial halo sign (a radiolucent line around the implant > 1 mm
wide) followed by a double halo sign on anteroposterior radiographs or CT scans was defined as screw loosening2-4,12,20 (Fig.
3). The measurement was performed using quantitative measurement analysis software (SmartIris, Taiwan Electronic Data
Processing Co.) For any ambiguity, the CT scan was reviewed
with radiologists for the final determination of a halo sign.
3. Statistics
Medcalc (Ostend, Belgium) was used for statistical analysis.
Descriptive statistics were reported as means and standard deviations, and as frequencies and percentages where appropriate.
Continuous variables were compared using an unpaired Student t-test, and categorical variables were compared using Pearson chi-square test. Probability values were 2-tailed and an alpha of 0.05 was considered statistically significant.
2. Perioperative Parameters and Clinical Improvement
In this study, patients of the CBT-based group used significantly less operation time for both 1-level and 2-level surgery
(163.2 ± 26.6 minutes vs. 196.9 ± 62.1 minutes, p = 0.005 and
227.1 ± 43.1 minutes vs. 257.7 ± 75.3 minutes, p = 0.04, respectively) than the pedicle-based group. The CBT-based group also
had significantly less blood loss for 1-level and 2-level surgery
(173.2 ± 157.2 mL vs. 399.1 ± 303.3 mL, p < 0.001 and 353.7 ±
248.8 mL vs. 816.8 ± 463.7 mL, p < 0.001, respectively) than the
pedicle-based group (Table 2).
Both groups demonstrated significant improvement in VAS
for back and leg pain, and ODI scores. Moreover, both groups
demonstrated similar scores in VAS for back pain (2.3 ± 2.5 vs.
2.2± 2.5, p= 0.88), VAS for leg pain (2.1± 2.7 vs. 2.5± 2.5, p= 0.62),
and ODI scores (19.6 ± 17.3 vs. 15.5 ± 10.8%, p = 0.43) at the final follow-up, 24 months after surgery (Fig. 4).
RESULTS
1. Demographics
A total of 291 consecutive patients were included in this study.
The first 235 patients received pedicle-based DS and the later
Table 1. Demographics
Pedicle-based
DS
Variable
CBT-based
DS
p-value
No. of patients
235
56
Mean age (yr)
61.7 ± 10.9
62.5 ± 10.4
0.61
117:118
27:29
0.83
Hypertension
100
21
0.49
Diabetes mellitus
51
9
0.35
25.8 ± 3.8
25.7 ± 2.4
0.92
Sex, male:female
Body mass index (kg/m )
2
Level
Table 2. Comparison of perioperative parameters
Variable
0.82
L3/4
14
4
L4/5
93
24
L3/4/5
128
28
Pathology
116
27
Spondylolisthesis
119
29
61.8 ± 34.9
31.2 ± 6.1
CBT-based
DS
p-value
1 Level
196.9 ± 62.1
163.2 ± 26.6
0.005*
2 Levels
257.7 ± 75.3
227.1 ± 43.1
0.04*
1 Level
399.1 ± 303.3
173.2 ± 157.2
< 0.001*
2 Levels
816.8 ± 463.7
353.7 ± 248.8
< 0.001*
EBL (mL)
< 0.001*
Values are presented as mean ± standard deviation.
DS, dynamic stabilization; CBT, cortical bone trajectory; EBL, estimated blood loss.
*p < 0.05.
Values are presented as mean ± standard deviation or number.
DS, dynamic stabilization; CBT, cortical bone trajectory.
*p < 0.05.
https://doi.org/10.14245/ns.2244888.444
Pedicle-based
DS
Operation time (min)
0.87
Spondylosis
Follow-up (mo)
3. Screw Loosening, Fracture, and Other Complications
There was no breach of the screws that caused symptoms or
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311
Pr
eo
6W p
e
3 M eks
on
6 M ths
o
12 nth
M s
o
18 nth
M s
o
24 nths
M
on
th
s
*
Pr
eo
6W p
e
3 M eks
on
6 M ths
o
12 nth
M s
o
18 nth
M s
o
24 nths
M
on
th
s
*
ODI
55
50
45
40
35
30
25
20
15
10
5
*
Pr
eo
6W p
e
3 M eks
on
6 M ths
o
12 nth
M s
o
18 nth
M s
o
24 nths
M
on
th
s
VAS leg
8
7
6
5
4
3
2
1
0
CBT DS
*
CBT DS
VAS back
Pr
eo
6W p
e
3 M eks
on
6 M ths
o
12 nth
M s
o
18 nth
M s
o
24 nths
M
on
th
s
CBT DS
8
7
6
5
4
3
2
1
0
*
ODI
55
50
45
40
35
30
25
20
15
Pr
eo
6W p
e
3 M eks
on
6 M ths
o
12 nth
M s
o
18 nth
M s
o
24 nths
M
on
th
s
*
VAS leg
8
7
6
5
4
3
2
1
0
Pedicle DS
VAS back
Pedicle DS
8
7
6
5
4
3
2
1
0
Cortical Bone Trajectory Dynamic Stabilization
Pr
eo
6W p
e
3 M eks
on
6 M ths
o
12 nth
M s
o
18 nth
M s
o
24 nths
M
on
th
s
Pedicle DS
Chang CC, et al.
Fig. 4. The patient-reported outcomes demonstrated equivalent clinical improvements between the 2 groups. VAS, visual analogue scale; ODI, Oswestry Disability Index; DS, dynamic stabilization; CBT, cortical bone trajectory. *The score at 24 months
after surgery was significantly lower than preoperation (preop).
required revision surgery in the entire series. In the pedicle-based
group, there were 108 loosened screws (9%) in 62 patients (26.4%),
which was significantly higher than that in the CBT-based group
(15 screws [5.4%] in 7 patients [12.5%], p = 0.045 and 0.028, respectively). Moreover, there were 7 fractured screws (0.6%) in 5
patients (2.1%) in the pedicle-based group, while there were
none in the CBT-based group (Table 3).
Other surgical complications (e.g., incidental durotomy, superficial or deep wound infections) were similarly low in both
groups. There were 3 wound infections and 3 incidental durotomies in the CBT DS group. On the other hand, there were 13 incidental durotomies, 2 wound infections, and 1 epidural hematoma in the pedicle-based DS group. There was no newly-onset
foot-drop or other lumbosacral radiculopathy causing weakness
after surgery in both groups. In pedicle-based DS group, there
were 38 patients had ASD. Among them, 6 patients had revision
fusion surgery. Three patients had progressed spondylolisthesis
over the index level. In CBT-based DS group, there were 2 patients had asymptomatic ASD. One patient had recurrent disc
over the index level that revision fusion surgery was performed.
4. Effects of Screw Loosening
Comparisons were made between the intact and loosened
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Table 3. Analysis of screw loosening
Pediclebased DS
Variable
Loosen screw
108 (9.0)
Nonloosen screw
1,088 (91)
Patients with loosen screw
Patients without loosen screw
CBT-based
p-value
DS
15 (5.4)
0.045*
265 (94.6)
62 (26.4)
7 (12.5)
173 (73.4)
49 (87.5)
0.028*
Fractured screw
7 (0.6)
0 (0)
0.19
Patients with fractured screw
5 (2.1)
0 (0)
0.27
Values are presented as number (%).
DS, dynamic stabilization; CBT, cortical bone trajectory.
*p < 0.05.
screws in and between both the CBT-based and pedicle-based
groups. In the CBT-based DS group, most of the demographic
data demonstrated no differences, except that patients with screw
loosening were older than those without. In the pedicle-based
DS group, with or without screw loosening, there were no differences in patients’ age, BMI, or bone density. However, there
was a male predominance of screw loosening in pedicle-based
DS for uncertain reasons. At 24-month postoperation, there
were no differences between the subgroups of loosened and intact screws, within both the pedicle-based or CBT-based groups.
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Cortical Bone Trajectory Dynamic Stabilization
Table 4. Comparison of loosened screw and intact group
Variable
Age (yr)
Pedicle-based DS Screw loosening
Yes (n = 62)
No (n = 173)
p-value
Yes (n = 7)
No (n = 49)
p-value
62.4 ± 11.3
61.5 ± 10.9
0.57
70.1 ± 5.8
61.5 ± 10.5
0.04*
Sex
Male
Female
BMI (kg/m2)
Diabetes mellitus
DEXA T score
CBT-based DS Screw loosening
0.03*
38
79
0.61
4
23
24
94
3
26
26.1 ± 4.1
25.7 ± 3.7
0.63
25.4 ± 2.5
25.7 ± 2.3
0.71
13
38
0.87
2
7
0.34
-0.36 ± 1.6
-0.56 ± 1.5
0.52
-0.98 ± 1.1
-0.56 ± 1.5
0.58
5.7 ± 3.1
5.6 ± 3.2
0.81
1.5 ± 1.0
3.7 ± 3.2
0.17
5 ± 3.4
0.19
Preoperation
VAS back
VAS leg
6.8 ± 2.4
6.3 ± 3.1
0.35
2.5 ± 3.7
52.7 ± 16.1
48.7 ± 19.5
0.19
20.5 ± 8.6
28.1 ± 17.3
0.41
VAS back
2.1 ± 2.6
2.2 ± 2.4
0.83
2.5 ± 3.5
2.2 ± 2.2
0.87
VAS leg
1.7 ± 2.4
2.2 ± 2.7
0.4
2.5 ± 3.5
2.2 ± 2.8
0.89
17.6 ± 16.1
20.3 ± 17.7
0.39
18 ± 8.4
9.2 ± 10.1
0.27
ODI
24-Month postoperation
ODI
Values are presented as mean ± standard deviation or number.
DS, dynamic stabilization; CBT, cortical bone trajectory; BMI, body mass index; DEXA, dual-energy x-ray absorptiometry; VAS, visual analogue scale; ODI, Oswestry Disability Index.
*p < 0.05.
The loosened screws had no adverse effects on the patient-reported outcomes (Table 4).
the design rationale of screw-based DS to preserve motility by
preservation of muscles. The invention of adapting CBT for DS
was first attempted by the authors with a promising preliminary
report.31 Most of the series of CBT used cortical screws in lumbar fusion, and both the trajectory and design of the screws could
have enhanced the purchase. Although the original design of
screws of DS was similar to common PSs rather than cortical
screws, the novel trajectory reportedly plays a more important
role than the screw per se.33
The concept of preservation of motion in surgery for lumbar
degeneration has gained popularity outside North America. Most
of the reported series of DS came out of Europe and the AsiaPacific region. Several reports demonstrated satisfactory and
noninferior outcomes of DS compared to that of lumbar fusion
surgery.16,34 The historic concern that the DS screws were subject to loosening after repeated load challenge has been addressed with little clinically significant consequences.21,35,36 Stoll
et al.10 reported 10 loose screws (3.6%) in 7 of 83 patients (8.4%)
at a mean follow-up of 38.1 months. Grob et al.23 reported on
screw loosening in 4 of 31 patients (13%) at a 2-year follow-up,
and all these patients underwent reoperation. Bothmann et al.1
documented screw loosening in 7 of 40 patients (17.5%). Furthermore, they reported a case with screw breakage at 21 months
DISCUSSION
This series demonstrated that CBT is a feasible alternative to
pedicle trajectory for DS, with less soft tissue dissection and
higher strength of the screws. The novel CBT DS had less incidence of screw loosening in the current series compared to the
conventional DS. The CBT was first described by Santoni et
al.26 in 2009 as a novel method for PS placement in lumbar surgery. Biomechanical studies demonstrated the superiority of
the CBT, which could yield a 30% increase in pullout strength
and a 71% increase in insertional torque.26,32 Using CBT could
theoretically enhance bony integration at the bone-screw interface and reduce the incidence of screw loosening. Because CBT
uses an entry point at the pars interarticularis and a medial-tolateral trajectory, it inherently allows avoidance of a wide exposure of the transverse process or muscle detachment at both index and cephalad facet joints. Minimizing muscle detachment
from the facet joint could maintain structural integrity of the
facet joint and would likely help to reduce future ASD. The features of CBT, less soft tissue violation, coincidentally matches
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Chang CC, et al.
after surgery. Schaeren et al.8 reported 3 of 19 patients (15.7%)
with screw loosening at a 4-year follow-up. Additionally, 1 of 19
patients (5.2%) experienced screw breakage. They also pointed
out neither screw breakage nor screw loosening was related to
the patients’ satisfaction or back pain. Wu et al.12 documented
31 cases (4.7%) of screw loosening in 25 of 126 patients (19.8%),
with a mean follow-up of 37 months. Most of the rates reported
for screw loosening range from 10% to 20% of the patients and
seldom require revision surgery. This feature of DS is distinct
from the arthrodesis series, in which screw loosening often causes
pseudarthrosis warranting reoperation. The biggest difference
between fusion surgery and DS is that the facet should be preserved as much as possible in DS to prevent iatrogenic instability. Once the screw loosening occurred in DS, the preserved facet joint could still provide enough support to prevent the progression of instability. This might be the reason why the revision
surgery was seldom required in DS patients with screw loosening. Nonetheless, minimization of screw loosening and enhancement of osteointegration are certainly important for DS. In the
present study, CBT-based DS demonstrated superior screw integrity, with lower rates of screw loosening than the pedicle trajectory (12.5% vs. 26.4%, p = 0.028). The subgroup analysis also
demonstrated that the screw loosening rates were lower in the
CBT-based group than the pedicle-based group in any of the
subgroup analyses. Moreover, there was no screw breakage in
the CBT-based group, compared with 7 screws (0.6%) broken
in 5 patients (2.1%) in the pedicle-based group. In our experience, the utilization of the new trajectory yielded a lower screw
loosening rate and breakage in DS. Furthermore, at 24-month
postoperation, all the clinical outcomes, including the VAS for
back and leg pain, and the ODI scores, demonstrated equally
significant improvement in all subgroups, which were also compatible with the published series.
There were limitations to the study. This was a single institute,
retrospective, nonrandomized, comparison study. The 2 cohorts
were enrolled with the same indication but at different time points.
There was study bias in that the pedicle-based cohort had a significantly longer follow-up which may have influenced the occurrence of screw loosening. However, all the complication profiles were analyzed with equal scrutiny, and the time point of
screw loosening always occurred within 24 months after surgery.
Since all patients in this study had a minimum of 2 years of follow-up, the influence of unequal follow-up on the occurrence of
screw loosening would be minimal and omissible. Furthermore,
the DS screws used in the 2 subgroups were slightly different.
Not only the diameters but also the lengths of the screws for the
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CBT and PSs were different by design. The CBT-based group
used shorter and smaller screws. However, this was compatible
with all the published series of CBT screws that were used for fusion. Whether the differences of screw size and shape matter in
DS as in fusion constructs remain elusive. Investigations with a
longer follow-up and larger sample sizes are warranted to understand the long-term outcome of the novel strategy.
CONCLUSION
The CBT-based DS for 1- or 2-level lumbar degenerative disease demonstrated equivalent clinical improvements as the pedicle-based DS. The adoption of CBT-based screws for DS could
be a less invasive approach (shorter operation time and less blood
loss), with lower chances of screw loosening than the conventional PS-based DS.
NOTES
Conflict of Interest: The authors have nothing to disclose.
Funding/Support: This study received no specific grant from
any funding agency in the public, commercial, or not-for-profit
sectors.
Author Contribution: Conceptualization: CCC, THT, WCH,
JCW; Data curation: CCC, HKC, CCK, CLW, YHK; Formal
analysis: CCC, HKC, CCK, CLW, YHK; Methodology: CCC,
HKC, CCK, CLW, YHK, THT, WCH, JCW; Project administration: THT, WCH, JCW; Writing - original draft: CCC; Writing
- review & editing: CCC, THT, WCH, JCW.
ORCID
Chih-Chang Chang: 0000-0003-2785-0921
Hsuan-Kan Chang: 0009-0004-6893-187X
Chin-Chu Ko: 0000-0003-3061-1059
Ching-Lan Wu: 0000-0001-9231-6288
Yi-Hsuan Kuo: 0000-0002-03553-4476
Tsung-Hsi Tu: 0000-0002-0550-5855
Wen-Cheng Huang: 0000-0003-4249-710X
Jau-Ching Wu: 0000-0002-6996-3409
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