The European Robotic Spinal Instrumentation (EUROSPIN) Study: A European Prospective Multicenter Multinational Pragmatic Trial on Robot-guided Versus Navigated Versus Freehand Pedicle Screw Fixation
Conditions: Degenerative Disc Disease, Spondylolisthesis, Spinal Stenosis, Recurrent Disc Herniation, Spondylodiskitis, Spinal Tumor, Spinal Metastases
Sponsor: Marc Schröder

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Cover Page 
 
Title: The European Robotic Spinal Instrumentation (EUROSPIN) study: Protocol for a multicenter 
prospective observational study of pedicle screw revision surgery after robot-guided, navigated, and 
freehand thoracolumbar spinal fusion 
 
NCT Number: NCT03398915 
 
Date: 8th September 2019

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The European Robotic Spinal Instrumentation (EUROSPIN) study: 
Protocol for a multicenter prospective observational study of pedicle screw revision surgery after 
robot-guided, navigated, and freehand thoracolumbar spinal fusion 
 
Victor E. Staartjes*1,2,3, BMed; Granit Molliqaj*4, MD; Paulien M. van Kampen5, PhD; 
Hubert A.J. Eversdijk1, BSc; Aymeric Amelot6, MD, PhD; Christoph Bettag7, MD; 
Jasper F.C. Wolfs8, MD; Sophie Urbanski9; Farman Hedayat9, MD; Carsten G. Schneekloth10, MD; 
Mike Abu Saris11, MD; Michel Lefranc12, MD, PhD; Johann Peltier12, MD, PhD; 
Duccio Boscherini13, MD; Ingo Fiss7, MD; Bawarjan Schatlo7, MD; Veit Rohde7, MD;  
Yu-Mi Ryang14,15, MD; Sandro M. Krieg14; MD, MBA; Bernhard Meyer14, MD;  
Nikolaus Kögl16, MD, MSc; Pierre-Pascal Girod16, MD; Claudius Thomé16, MD;  
Jos W.R. Twisk17, PhD; Enrico Tessitore*4, MD; Marc L. Schröder*1, MD, PhD 
 
1Department of Neurosurgery, Bergman Clinics Amsterdam, Amsterdam, The Netherlands 
2Department of Neurosurgery, Clinical Neuroscience Center, University Hospital Zurich, University of 
Zurich, Zurich, Switzerland 
3Amsterdam UMC, Vrije Universiteit Amsterdam, Neurosurgery, Amsterdam Movement Sciences, 
Amsterdam, The Netherlands  
4Department of Neurosurgery, Geneva University Hospital (HUG), Geneva, Switzerland 
5Department of Epidemiology, Bergman Clinics Amsterdam, Amsterdam, The Netherlands 
6Department of Neurosurgery, La Pitié Salpétrière Hospital, Paris, France 
7Department of Neurosurgery, Medical Center, Georg August University of Göttingen, Göttingen, 
Germany 
8Department of Neurosurgery, Haaglanden Medical Center, The Hague, The Netherlands 
9Center for Spinal Surgery and Pain Therapy, Ortho-Klinik Dortmund, Dortmund, Germany 
10Department of Spinal Surgery, St. Josef Brothers Hospital, Paderborn, Germany 

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11Department of Neurosurgery, Martini Hospital, Groningen, The Netherlands 
12Department of Neurosurgery, Amiens University Hospital, Amiens, France 
13Department of Neurosurgery, Clinique de La Source, Lausanne, Switzerland 
14Department of Neurosurgery, Klinikum rechts der Isar, Technical University Munich, Munich, Germany 
15Department of Neurosurgery, HELIOS Klinikum Berlin-Buch, Berlin, Germany 
16Department of Neurosurgery, Medical University of Innsbruck, Innsbruck, Austria 
17Amsterdam UMC, Vrije Universiteit Amsterdam, Department of Epidemiology and Biostatistics, 
Amsterdam, The Netherlands 
 
Study Sponsor and Principal Investigator 
Marc L. Schröder, MD, PhD 
Department of Neurosurgery 
Bergman Clinics, Amsterdam, The Netherlands 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

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Introduction 
In the Unites States alone, an estimated 3.6 million spinal instrumentations were performed between 2001 
and 2010, with an associated $287 billion in total healthcare charges.[1] Both numbers demonstrate a 
steadily increasing trend.[1] In 2013, only 11% of spine surgeons routinely used navigation systems.[2] 
Meanwhile, more and more surgeons are implementing computer assistance into their clinical practice, 
one reason being the adoption of minimally invasive (MI) techniques, further increasing the need for 
navigation due to often inexistent line-of-sight.[2,3]  
 
In 1995, the concept of computer-assisted navigation was introduced to spine surgery.[4] Modern 
navigation systems (NV) assist in pedicle screw insertion by projecting screw trajectories onto pre- or 
intraoperatively obtained and co-registered computed tomography (CT) or 3D-fluoroscopic (3DFL) 
images.[5] Robotic guidance (RG), introduced in 2006, takes one further step by providing mechanical 
guidance according to pre-planned screw trajectories, eliminating the need of on-the-spot establishment of 
trajectories by the surgeon.[6–8] These systems can be considered cooperative robots (“cobots”), since 
they do not insert screws autonomously, rather exclusively providing stable guidance.[9] To achieve 
mechanical guidance, the robot’s working channel moves into the pre-planned trajectory based on co-
registration of preoperative and intraoperative imaging while accounting for any potential differences in 
real-time spinal anatomy such as those caused by distraction, cage insertion, or changes between the 
supine positioning on preoperative CT and prone positioning during surgery.[6–8,10,11] By restricting 
the surgeon’s natural full motion range of 6 degrees of freedom (DOF) to 2 DOFs – motion up and down 
as well as yaw in the cannula – the robot guides the surgeon’s tool according to the pre-defined 
trajectories while simultaneously providing stability for drilling, which is assumed to result in greater 
radiological screw accuracy.[6] When comparing the published literature on FG, NV, and RG, rates of 
radiologically well-placed screws of 69%-94% for FH, 81%-100% for NV, and 85% to 98% for RG are 
found[6,10–15], with significant differences among subgroups of various NV devices.[16] 
 

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While there is some evidence that RG and NV lead to higher radiological accuracy than freehand (FH) 
instrumentation [12,16–21], this may not translate directly to real-world clinical benefits, especially in 
light of the high acquisition and maintenance costs inherent to these systems.[22] A recent systematic 
review on the cost-effectiveness of RG concluded that, although the technology is often claimed to be 
cost-effective, there appears to be a lack of published data to warrant this statement.[22] Possible benefits 
could include shorter operating times, and decreased incidences of radiculopathy and costly revision 
surgery for screw malposition, although the current level of evidence is very low, and there are no large 
prospective controlled studies comparing clinically relevant outcome such as pedicle screw-related 
revision surgery, as opposed to radiological surrogate measures alone.[5,6,14,21–30]  
 
Currently, few published studies compare these techniques in a prospective setting, although they often 
suffer from insufficient power to demonstrate any potential clinical benefits, or report major conflicts of 
interests. Furthermore, while many studies compare RG to FH, there are no powerful studies comparing 
RG and NV.[5] We aim to conduct a prospective observational controlled study comparing RG, NV, and 
FH to create real-world evidence on these instrumentation techniques.[31] 
 
 
 
 
 
 
 
 
 
 
 

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Methods and Analysis 
Study Design 
The European Robotic Spinal Instrumentation (EUROSPIN) study is a prospective, international, 
multicentre, pragmatic, open-label, non-randomized, observational controlled study comparing the 
effectiveness of three techniques for pedicle screw instrumentation, namely RG, NV (CT-, O-Arm, or 
3DFL-based), and FH.[31–33] Following the baseline evaluation, patients receive pedicle screw fixation 
by the senior surgeons on the author’s list, and are subsequently followed up for 24 months. The primary 
analysis is conducted using the 12-month data. The study is designed to evaluate the superiority of RG 
and NV over FH in terms of the time to revision surgery for a malpositioned or loosened pedicle screw 
within the first postoperative year. This study protocol is compiled according to the Standard Protocol 
Items: Recommendations for Interventional Trials (SPIRIT) Statement.[34] Thirteen European centers 
from the Netherlands, Switzerland, Germany, Austria, and France participate in recruitment. Most centers 
contribute to at least two of the three study arms. 
 
Study Population 
Inclusion Criteria 
Patients with the following indications for thoracolumbar pedicle screw placement are considered for 
inclusion: Degenerative pathologies (spinal stenosis, spondylolisthesis, degenerative disc disease, 
recurrent disc herniation), infections, vertebral tumors, as well as traumatic and osteoporotic fractures. 
Patients are required to give informed consent. Only patients aged 18 or older are considered for 
inclusion.  
 
Exclusion Criteria 
Patients undergoing deformity surgery for scoliosis or kyphosis are not eligible. Patients undergoing 
surgery at more than 5 vertebral levels are also not eligible. 
 

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Patient and Public Involvement  
Patients were not involved in the development of the research question or study design, and will not be 
involved in recruitment or conduct of the study. 
 
Study Procedures 
Participating surgeons screen all patients with an indication for thoracolumbar pedicle screw placement 
for eligibility during the first consultation. If eligible, the patient receives an informative letter containing 
details on the EUROSPIN study after surgical consent has been given, including risks and benefits of 
participation. If written informed consent for study participation is given, the clinician or study nurse 
records baseline data. At this first visit, group allocation is determined. 
 
Group Allocation 
This is a non-randomized study. In this study, patients are not randomly allocated to treatment and control 
groups. Instead, patients undergo pedicle screw placement with the technique that the treating surgeon is 
most experienced with, and for which equipment is available at the center.[31] One reason concerns the 
surgeons’ level of experience with a particular technique.[14,27,35,36] Because it has been demonstrated 
that the learning curve for some instrumentation techniques is steep, we did not deem it rational to have 
surgeons carry out procedures with a technique that they are not experienced with.[37] Instead, surgeons 
carry out the procedures with the technique that they are highly experienced with. This allows us to 
compare true effectiveness, similar to a prospective registry, as opposed to efficacy.[33] We have not 
implemented a pre-study “learning curve” phase, accordingly. A second reason is recruitment. Although 
some randomized controlled trials on robotic guidance in spinal instrumentation have been successful 
[14,38,39], they have suffered from rather slow recruitment and consequently relatively low power to 
demonstrate differences in an infrequently occurring endpoint, such as our primary endpoint. Multiple 
initialized randomized studies even had to be closed prematurely due to slow recruitment.[29]  
 

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Blinding 
This is an open-label study. Both patients and treating physicians are aware of group allocation. However, 
the primary analysis is carried out by an epidemiologist blinded to group allocation, according to the pre-
specified statistical protocol. Rating of CT images is carried out by independent radiologists blinded to 
group allocation. 
 
Treatment Groups 
Experimental Intervention I: Robot-guided pedicle screw placement 
Robotic guidance in the form of the following systems is applied: Mazor X, Renaissance, or SpineAssist 
(Mazor Robotics, Ltd., Ceasarea, Israel) or ROSA Spine (Zimmer Biomet, Warsaw, IN, 
USA).[5,6,14,25,26,28] Fluoroscopic control is available. 
 
Experimental Intervention II: Navigated pedicle screw placement 
Navigated procedures are carried out under image guidance connected to a computer-assisted navigation 
system.[4,5,23] Preoperative or intraoperative image acquisition by spiral CT, cone-beam CT (O-Arm), or 
three-dimensional isocentric flurosocopy (3DFL) is applied for navigation.[4,5,23,40–42] Fluoroscopic 
control is available. 
 
Control Intervention: Freehand pedicle screw placement 
Conventional freehand surgery was chosen as the comparator because it is currently the most widely used 
and accepted standard technique around the world.[2] Freehand procedures are carried out according to 
surgeon preference, under fluoroscopic control.[5,14,19,23,25,26,28,40] Computer assistance is not 
available. 
 
 
 

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Cointerventions 
Analgesic medication is available to the patients, if necessary. In addition, patients are able to undergo 
any further desired cointerventions such as elastic corsets or rigid casts, physiotherapy, or others.  
 
Prognostic Factors 
At the baseline assessment, patient age, height, weight, BMI, history of back or leg pain in months, prior 
surgery at any of the index levels, as well as highest level of education (elementary/high school/higher 
education/(post-)doctoral) and type of work (employed/self-
employed/housework/student/retired/unemployed) are recorded. We also assess the use of analgesic 
medication (daily/at least once a week/not regularly) including over-the-counter drugs, patient satisfaction 
with current symptoms on a 3-step Likert scale (satisfied/neutral/dissatisfied), smoking status (active 
smoker/ceased/never smoked), and working status (able to work/unable to work/not applicable). 
Documented osteoporosis with or without treatment is recorded, as well as any procedures for 
osteoporotic fractures. 
 
Outcome Measures 
Primary Endpoint 
We defined the primary endpoint as time to revision surgery for a malpositioned or loosened pedicle 
screw within the first postoperative year. In patients who experience the primary endpoint, CT imaging is 
carried out before revision surgery, and the degree of malposition is graded according to the classification 
described by Gertzbein and Robbins.[43] 
 
Secondary Endpoints 
A range of secondary endpoints is assessed. The following patient-reported outcome measures (PROMs) 
are captured at baseline and follow-up: Numeric Rating Scales (NRS) for back pain severity (NRS-BP) 
and leg pain severity (NRS-LP), as well as validated translations of version 2.1 of the Oswestry Disability 

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Index (ODI) for subjective functional impairment, and the three-level version the EuroQOL 5-dimensions 
(EQ-5D-3L) questionnaire (EQ-5D index and thermometer) for health-related quality of life 
(HRQOL).[44] The EQ-5D index is evaluated according to the respective national tariffs.[45] The 
proportion of patients in which revision or redirection of a pedicle screw was required intraoperatively 
(intraoperative revision) is recorded, as well as the number of instrumented index levels per patient. We 
record whether the procedure was carried out in a minimally invasive or open approach, and capture 
duration of the procedure in minutes, total intraoperative fluoroscopic radiation dose as dose area product 
(DAP) in mGy × cm2, estimated blood loss in mL, need for blood transfusion, as well as any 
intraoperative or postoperative adverse events. We also record the level of experience of the surgeon 
placing the pedicle screws (resident/fellow/board-certified ≤ 10 yrs./board-certified > 10 yrs.). 
Conversions from one study arm to another, as well as from minimally invasive to open surgery are 
tracked. All serious adverse events (SAEs) are reported to the principal investigators’ site. 
 
Follow-Up 
Patients undergo an “early” follow-up at one to three months. Subsequently, patients are followed-up at 
12 months and 24 months postoperatively (Table 1). At follow-up, PROMs, use of analgesic medication, 
satisfaction with symptoms, smoking status, time to return to work in weeks, as well as any reoperations 
are captured. 
 
Data Collection 
Data are collected using a validated, secure web-based electronic data capturing system (CASTOR EDC, 
Amsterdam, The Netherlands). Each center is able to enter anonymized data into an Electronic Research 
Form (eCRF). Investigators from each center assign identifiers to patients, and store demasking lists. For 
follow-up of patient-reported outcome measures (PROMs), centers also have the option of dispatching 
standardized, scheduled surveys directly to the patients.[46] All data handling (data entry, storage, and 

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analysis) is confidential and complies with data protection regulations of participating countries and the 
European Union. Deidentified data is stored for 15 years. 
 
Sample Size Calculation 
It was determined that, to detect an absolute intergroup difference of 5% in the primary endpoint, 205 
patients are required per group to achieve a power of 1 -  = 0.8 at  = 0.05.[47] Recruitment for a specific 
arm is stopped once the 205 patients have been included. The incidence rates are based on the published 
literature, with an approximated incidence rate of the primary endpoint of approximately 0% for the 
intervention and 5% for the control group.[5,6] Because the study protocol is in line with the normal clinical 
follow-up protocol of most centers, a low dropout rate is expected. This leads to a minimum total sample 
size of 615 patients.  
 
Statistical Analysis 
Overview 
All analyses are carried out in R (The R Foundation for Statistical Computing).[48] A p ≤ 0.05 on two-
tailed tests is considered statistically significant. The primary analysis, conducted on the 12-month data, is 
carried out according to the intention-to-treat principle, with the intention-to-treat definition applying to 
the index surgery.[49] Results are reported as effect size estimates and their 95% confidence intervals. 
 
Analysis of Primary Endpoint 
The effect on the primary endpoint is reported as hazard ratios and their 95% confidence intervals, 
calculated from crude and adjusted Cox proportional hazards models. The crude model is considered the 
primary analysis. The primary endpoint is specified as the dependent variable, and group assignment as 
the independent variable, with the FH group as the reference category. Our null hypothesis is that neither 
RG nor NV lead to a significant decrease in the primary endpoint incidence compared to FH. Patients 

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who do not experience a primary endpoint are censored at the 12-month follow-up, with respect to the 
primary endpoint only. 
 
Analysis of Secondary Endpoints 
PROMs (NRS-BP, NRS-LP, ODI, EQ-5D) are analysed using baseline-adjusted linear mixed models. 
The mean overall effect over time, as well as effects at the specific follow-up timepoints, are estimated. 
The proportions of patients achieving MCID for each PROM, as well as proportions of patients reporting 
satisfaction, return to work, reoperations, and using analgesic medication are reported. MCIDs for the 
ODI, NRS-BP, and NRS-LP are defined as a reduction of ≥ 30% according to Ostelo et al.[50] The MCID 
threshold for the EQ-5D is set to 0.2 points according to Asher et al.[51] Return to work and overall 
reoperations are statistically analysed using crude and adjusted Cox proportional hazards models. In 
addition, intergroup comparison is performed for patient satisfaction and use of analgesic medication by 
logistic regression. 
 
Subgroup Analysis 
Prespecified subgroup analyses of the primary outcome are performed in the intention to-treat population 
to test for an interaction between study group and the subgroup variable. Stratified analyses are performed 
by indication for surgery, specific device used [16], type of exposure, as well as single-level or multi-
level fusion. 
 
Monitoring 
Monitoring is performed according to the pre-specified monitor plan. An epidemiologist from the sponsor 
institution organizes an initiation monitor visit at every participating center before starting recruitment. 
This monitor visit checks whether all study staff are properly trained and the delegation of tasks are well 
documented (complete Investigator Site File, training and delegation logs). An additional audit is carried 
out at 6 months after initiation of recruitment to check whether source documentation and eCRF 

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documentation is similar. Throughout the entire study, additional queries by the monitor are sent to the 
investigator in the data capturing system to ensure proper data capturing. 
 
Expected Completion 
Recruitment is expected to be completed by January 2021, with the 2-year follow-up period extending to 
January 2023 for the final results. 
 
Ethics and Dissemination 
Ethical Approval and Study Registration 
The study protocol is approved by the appropriate national and local authorities. Written informed 
consent is obtained from all participants. This study is registered at ClinicalTrials.gov under the identifier 
NCT03398915. 
 
Dissemination 
The final results will be published in an international peer-reviewed scientific journal, and communicated 
to study participants. No interim analyses have been specifically planned. To avoid any bias, the results of 
any interim analyses are neither shared with the investigators nor published until recruitment has been 
completed. There are no further restrictions to publication. 
 
 
 
 
 
 
 
 

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Discussion 
The EUROSPIN study is a large, multicentre, pragmatic study that is aimed at resolving the discussion on 
whether computer assistance in thoracolumbar instrumentation leads to measurable and clinically relevant 
improvements in patient-reported clinical outcome or complication rate.  
 
Previous studies have created some evidence that both robotic guidance and navigation lead to a 
somewhat higher radiological accuracy than freehand pedicle screw insertion, with inconsistent results at 
a rather low level of evidence [12,14,16–21,23]. It is still unclear whether this increased radiological 
accuracy, usually measured as the degree of deviation from the desired transpedicular trajectory, 
translates to a clinical benefit to patients. It is hypothesized that, when using computer assistance, the 
lower rate of pedicular cortical encroachment leads to a lower incidence of radiculopathy [24,52], thus 
preventing revision surgery [6], decreasing overall treatment costs [53], and improving overall patient-
oriented outcomes.[38] A meta-analysis has demonstrated that both robotic guidance and navigation 
lower the incidence of revision surgery for malpositioned pedicle screws.[5] However, the rate of 
intraoperative screw revisions was markedly but not statistically significantly increased, the quality of the 
included individual studies was low, and it was determined that prospective studies assessing this research 
question with larger sample sizes are necessary to draw conclusions.[5] In addition, there are only very 
few, small studies comparing robotic guidance to navigation directly.[29,54] For these reasons, we 
designed our study to address these biases, and to provide higher-level evidence on clinical questions, 
comparing all three concepts of pedicle screw placement. 
 
A specific goal of the EUROSPIN trial is to avoid potential conflicts of interest.[55] Therefore, we 
decline any sort of direct involvement and study-related financial support by the industry, and aim to 
minimize personal conflict of interests with device manufacturers. This may enable execution and critical 
appraisal of the study results with less bias.[55,56] 
 

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The study has some limitations. First, for logistical and practical reasons, not all sites are able to 
contribute to all three study arms. This may create center bias. However, the rationale for this design is to 
prospectively collect data obtained from surgeons experienced with the three techniques, resulting in a 
design similar to a prospective multicentre registry. Furthermore, we are unable to conduct a detailed 
evaluation of cost-effectiveness. The cost-value relationship of robotic and intraoperative imaging 
systems remains controversial, and it is as of yet unclear if there are any demonstrable clinical benefits 
that warrant the high acquisition and maintenance costs inherent to these systems.[22] In addition, 
preoperative radiation that may be required for surgical planning may differ among the groups, and is not 
captured. In this light, it is important to consider that, even if the navigated and robotic techniques would 
result in decreased intraoperative radiation, this benefit to the patient may be levelled out by the 
additional radiation dose necessary for planning.  
 
Furthermore, although all participating surgeons are experienced with the respective techniques applied, 
as we do not specify a minimum case number for participating surgeons, surgeon experience may 
constitute a potential bias. We aim to correct for this potential bias by collecting data on the degree of 
experience of the surgeons placing the pedicle screws, which allows for statistical adjustment if 
necessary. Another potential limitation exists in the fact that thresholds for revision of a malpositioned or 
loosened screw may vary among centers and surgeons. Moreover, our study is likely underpowered for 
subgroup analyses analysing treatment effects among the single devices and the different indications for 
surgery. Lastly, some potential confounders such as comorbidities and symptom duration are not 
collected. 
 
Patients are not randomly assigned to treatment groups in the EUROSPIN study. As detailed above, there 
are two main reasons that randomization was deemed disadvantageous in this specific study. First, most 
centers do not have both a robotic system and conventional neuronavigation available, making it 
impossible to randomize to all three groups at every center. Furthermore, we aim to have the surgeons 

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perform the procedures with the technique they are most experienced with.[27,31,36] This enables us to 
compare the treatment modalities in a more clinically applicable scenario, assessing effectiveness instead 
of study-specific efficacy, similar to a prospective registry.[33] Accordingly, no “learning curve” phase 
was implemented. Even for randomized studies, Devereaux et al. suggest that surgeon-based or 
“expertise-based” group assignment, in which patients are not randomized to treatments but rather to 
clinicians experienced with a certain treatment, may lead to greater real-world applicability of study 
results.[31] In addition, some commenced randomized trials comparing robotic surgery with conventional 
techniques have had to be declared futile due to slow recruitment, usually because of a patient preference 
towards newer techniques. A split design, similar to the Spine Patient Outcomes Research Trial (SPORT), 
with a randomized and non-randomized subgroup was available as an alternative.[57] However, due to 
the aforementioned logistic difficulties and possible bias in experience, we have decided upon a simple, 
registry-like design for the EUROSPIN study. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

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26 
 
Tables 
Table 1 Chart demonstrating items collected at baseline and follow-up. 
Item 
Baseline 
Surgery 
Discharge 
1 to 3 months 
postop. 
12 months 
postop. 
24 months 
postop. 
Informed consent 
X 
 
 
 
 
 
Group allocation 
X 
 
 
 
 
 
Demographics  
X 
 
 
 
 
 
Surgeon experience 
 
X 
 
 
 
 
Surgery 
 
X 
 
 
 
 
Intraoperative parameters 
 
X 
 
 
 
 
Perioperative parameters 
 
X 
X 
 
 
 
Blood transfusion 
 
X 
X 
 
 
 
Length of stay 
 
 
X 
 
 
 
ODI 
X 
 
 
X 
X 
X 
NRS-BP + NRS-LP 
X 
 
 
X 
X 
X 
EQ-5D-3L 
X 
 
 
X 
X 
X 
Satisfaction (Likert) 
X 
 
 
X 
X 
X 
Work status 
X 
 
 
X 
X 
X 
Smoking status 
X 
 
 
X 
X 
X 
Use of analgesia 
X 
 
 
X 
X 
X 
Intraoperative screw revision 
 
X 
 
 
 
 
Revision surgery for screw 
malposition or loosening 
With occurrence 
Computed tomography 
With occurrence of revision surgery 
Adverse events 
With occurrence 
Reoperations 
With occurrence 
Other treatments 
With occurrence 
 
EQ-5D-3L, 3-level version of the EuroQOL five-dimensions questionnaire; NRS-BP, numeric rating scale for back 
pain severity; NRS-LP, numeric rating scale for leg pain severity; ODI, Oswestry Disability Index;