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XLIF interbody cage reduces stress and strain of fixation in spinal reconstructive surgery in comparison with TLIF cage with bilateral or unilateral fixation: a computational analysis

August 2019
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 2019

August 2019
2019

DOI:10.1109/EMBC.2019.8856592

Conference: IEEE EMBC
At: Berlin

Authors:

Teng Zhang

The University of Hong Kong

Siwei Bai

Technische Universität München

Socrates Dokos

UNSW Sydney

Jason Pui-Yin Cheung

The University of Hong Kong

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In treating recalcitrant low back pain, extreme lateral lumbar interbody fusion (XLIF) with a large cage is reported to have better stability compared to approach of transforaminal lumbar interbody fusion (TLIF) using a small cage. In addition, bilateral pedicle screw fixation (PSF) in comparison with unilateral fixation achieved no inferior fusion rate, but with a significant reduction in operation time and blood loss. The aim of the study was to understand the mechanism underpinning the stability of lumbar interbody fusion using different cage sizes with unilateral or bilateral PSF. A computer model of human lumbar vertebrae L4 and L5 with implants was reconstructed based on CT scans and simulated in Ansys Workbench. Simulation results demonstrated that for either XLIF or TLIF cages, the maximum values of rod stress were comparable with bilateral and unilateral PSF. However, the stability was considerably reduced with unilateral PSF for TLIF due to significantly increased facet joint strain for TLIF; whereas for XLIF with left unilateral PSF, the max facet joint strain was comparable to bilateral PSF, possibly due to facet tropism of this specific subject.

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Abstract—In treating recalcitrant low back pain, extreme

lateral lumbar interbody fusion (XLIF) with a large cage is

reported to have better stability compared to approach of

transforaminal lumbar interbody fusion (TLIF) using a small

cage. In addition, bilateral pedicle screw fixation (PSF) in

comparison with unilateral fixation achieved no inferior fusion

rate, but with a significant reduction in operation time and blood

loss. The aim of the study was to understand the mechanism

underpinning the stability of lumbar interbody fusion using

different cage sizes with unilateral or bilateral PSF. A computer

model of human lumbar vertebrae L4 and L5 with implants was

reconstructed based on CT scans and simulated in Ansys

Workbench. Simulation results demonstrated that for either

XLIF or TLIF cages, the maximum values of rod stress were

comparable with bilateral and unilateral PSF. However, the

stability was considerably reduced with unilateral PSF for TLIF

due to significantly increased facet joint strain for TLIF;

whereas for XLIF with left unilateral PSF, the max facet joint

strain was comparable to bilateral PSF, possibly due to facet

tropism of this specific subject.

I. INTRODUCTION

Low back pain (LBP) is a common health problem, with a

lifetime incidence of 80% [1]. The physical, psychological and

economical costs to the individuals that suffer from LBP affect

both their quality of life and workforce productivity. It is

believed that LBP results from pathological changes that occur

with lumbar degenerative diseases (LDD), including prolapsed

lumbar intervertebral disc (IVD), degenerative instability,

degenerative spondylolisthesis, degenerative scoliosis, and

lumbar spinal stenosis [2].

Extreme lateral lumbar interbody fusion (XLIF) is a

surgical approach to manage recalcitrant LBP not responding

to conservative treatment, with a view to relieve pain in this

population by eliminating pathologic motion [3] in diseased

spinal segments [2]. This is achieved by decompressing nerves

and reconstructing the lumbar spine with instrumentation

usually in the form of an interbody cage to restore the disc

height and screws and rods to stabilise the misaligned vertebra.

This procedure has gained popularity due to its minimal

invasive nature, and preserving the major spinal stability

Teng Zhang and Jason Cheung, Department of Orthopaedics and

Traumatology, Li Ka Shing Faculty of Medicine, University of Hong Kong,

Hong Kong, (Phone: +852 39176989, Fax: +852 28185210, email:

tgzhang.hku.hk);

Siwei Bai, Department of Electrical and Computer Engineering, Technical

University of Munich (TUM), Munich, Germany (email: siwei.bai@tum.de);

structures such as anterior longitudinal ligament (ALL) and

facet joints [4-6]. In comparison with the conventional

transforaminal interbody fusion (TLIF) approach, XLIF

allows interspace preparation and fusion to be completed

through a unilateral approach, achieving efficient

decompression, as well as allowing the placement of a larger

cage to reconstruct lumbar sagittal alignment [7].

A previous cadaveric study demonstrated that XLIF, when

compared to TLIF, showed reduced spinal range of motion and

thus improved stability post-operatively [8]. In addition to the

cage selection, clinical observational studies have shown that

compared to bilateral pedicle screw fixation (PSF), unilateral

PSF achieved no inferior fusion rate [9, 10], but a significant

reduction in operation time and blood loss [11]. However, the

clinical selection of the side of the unilateral fixation is unclear

due to the complexity and individual variance on the geometry

of vertebra. Specifically the facet tropism [12], which

demonstrates asymmetry of the bilateral facet joints, may

reduce the stability of a motion segment [13] and accelerate

the degenerative process of the IVD [14]. Thus when

performing the unilateral fixation, the standard of side

selection for the fixation remained unclear and whether facet

tropism may affect the clinical decision making remains

unproven [15].

Nonetheless, the underlying mechanisms behind the

fixation stability using different sizes of cages with unilateral

or bilateral PSF with facet tropism has not been investigated.

Precisely, the stress concentration of the instrumentation (i.e.

rods and screws) and the strain of the reconstructed vertebra

under loading are unknown. No computer simulations have

previously been done to understand the mechanisms.

Therefore, the aim of this computational study was to

understand the mechanism underpinning the stability of

lumbar interbody fusion using different anterio-posterior (AP)

measurements of cages with unilateral or bilateral PSF on

segments with facet tropism. We hypothesise that XLIF

provides superior stability, and no significant reduction of the

fixation stability using unilateral fixation compared to the

bilateral approach.

Socrates Dokos, Graduate School of Biomedical Engineering, University

of New South Wales (email: s.dokos@unsw.edu.au);

Ashish D Diwan, Spine Service, St George & Sutherland Clinical School,

University of New South Wales, Sydney, Australia, (email: a.diwan@spine-

service.org)

XLIF interbody cage reduces stress and strain of fixation in spinal

reconstructive surgery in comparison with TLIF cage with bilateral

or unilateral fixation: a computational analysis

Teng Zhang, Member IEEE, Siwei Bai, Member IEEE, Socrates Dokos, Member IEEE, Jason PY

Cheung, Ashish D Diwan

II. METHODS

A. Model Reconstruction

Anonymised CT scans of the human spine column at the

positions of L4 and L5 with facet tropism were acquired with

an isotropic voxel size of 1 mm. The segmentation of the CT

scans was performed in 3D Slicer (Version 4.8) [16], an open-

source platform for medical image processing. In 3D Slicer,

each tissue compartment was assigned a label map. To

generate a label map, a threshold was chosen for the gray level

of the pixel intensity at a single slice to automatically select

most of the desired tissue, and a paintbrush was used to

manually modify the selection. Facet tropism was identified

and measured to have a 15-degree angular difference [17].

A surface triangular mesh was generated for each

compartment (i.e. two vertebrae and the facet joints in

between) and transferred to Geomagic Studio. Due to the low

pixel intensity of soft tissues in CT scans, the anterior

longitudinal ligament was not included in the segmentation

process but reconstructed by using a spline approximation

connecting the frontal surfaces of the two vertebrae in

Geomagic Studio.

Two interbody cages (16 mm and 22 mm) were developed

in SolidWorks to represent cages used during TLIF (Figure

2A) and XLIF respectively (Figure 2B). A cylinder (length: 45

mm; diameter: 5.5 mm) was built as an idealized shape of the

PS implant and connected by a third cylinder (radius: 5.5 mm)

representing the rod. The cages and screws were placed into

the vertebrae at the similar position as during surgeries. All

surface meshes were converted into non-uniform rational basis

spline (NURBS) surface patches through a series of manual

procedures in Geomagic Studio.

B. Computerised biomechanical simulation

The surface models were then imported to Ansys

Workbench, a cross-platform finite-element (FE) solver, for

the analysis of the system stability under axial compression.

All compartments were modelled in accordance to their

mechanical properties found in the existing literature, as

shown in Table 1.

TABLE I. MECHANICAL PROPERTIES

Density

[kg/m3]

Young’s

Modulus

[MPa]

Poisson’s Ratio

Bone

1200

2.6e2

0.3

Facet joint

1020

0.4

ligament

1000

1.2e3

0.3

Cage (PEEK)

1320

3.9e3

0.4

Screw and Rod

(Titanium)

4430

1.138e5

0.342

In Ansys Workbench, a downward force with the

magnitude of 500 N was applied perpendicular to the upper

face of L4 body (Figure 3), simulating a static axial

compression on the vertebrae. The lower face of L5 body was

assumed at a fixed position, and all contacts between

compartments were assumed bonded.

III. RESULTS AND DISCUSSION

A. Comparison of TLIF and XLIF

Maximum stress of the system

The maximum stress presented at the rods with XLIF

comparing with TLIF utilizing bilateral PSF method was both

located on the rods and reduced 21% from 40.45 MPa to 32.07

MPa (Figure 3A vs. 3D). With both unilateral methods, the

maximum rod stress using XLIF was decreased (left: 26%

from 42.91 MPa to 31.77 MPa, Figure 3B vs. 3E; right: 30%

from 36.14 MPa to 25.12 MPa, Figure 3C vs. 3F) in

comparison with TLIF.

Maximum strain of the system

The maximum strain was shown at the facet joint and it

was reduced by 50% using the XLIF cage (0.12, Figure 4D)

compared to TLIF cage (0.18, Figure 4A) with bilateral

fixation. With unilateral fixation, the maximum facet joint

strain using XLIF was also decreased (left: 48% from 0.27 to

0.14, Figure 4B vs. 4E; right: 40% from 0.45 to 0.27, Figure

4C vs. 4F) in comparison with TLIF.

B. Comparison of bilateral and unilateral fixations

For TLIF, left unilateral fixation increased the max rod

stress by 6% (from 40.45 MPa to 42.92 MPa, Figure 3A vs

3B), whereas for XLIF (with large cage) the decrement was

small (decreased 0.9% from 32.07 MPa to 31.77 MPa, Figure

3D vs 3E). In the case of right unilateral fixation, the max rod

stress for both fusion approaches reduced drastically (TLIF:

decreased 11% from 40.45 MPa to 36.14 MPa; Figure 3A vs.

3C; XLIF: decreased 22% from 32.07 MPa to 25.14 MPa,

Figure 3D vs. 3F).

Figure 1. Facet tropism. Facet trapsim can be revealed with α = 25⁰

and β = 40⁰. The difference between these two facet joint angulations

was 15⁰. Tropism was defined as asymmetry of the left and right facet

joint angulations ≥ 8°.

αβ

025 50 (mm)

Figure 2. FE mesh models of L4/5 with different cage sizes. The

lateral view of the models show two vertebral bodies (in blue and

green) with either a TLIF cage or a XLIF cage in between. TLIF (A) is

with an anterio-posterior (AP) cage measurment of 16 mm, and XLIF

(B) is with an AP cage measurement of 22 mm. The number of FE

mesh elements number are 246,568 (A) and 258,228 (B).

A: TLIF (16mm cage) B: XLIF (22mm cage)

Rods

Facet joints

Cage

Vertebral

body

Cage

Vertebral

body

Rods

Facet joints

030 60 (mm) 030 60 (mm)

1888

For TLIF, the maximum facet joint strain increased 50%

and 150% respectively for left (0.27, Figure 4B) and right

(0.45, Figure 4C) unilateral fixations. In comparison, for XLIF

the maximum facet joint strain increased 17% and 125%

respectively for left (0.14, Figure 4E) and right (0.27, Figure

4F) PSF.

Our biomechanical simulation analysed the stability of

different lateral constructions for lumbar interbody fusion.

XLIF, with bilateral or unilateral PSF, provided improved

stability over TLIF constructs. Previous cadaveric study with

the Posterior Lumbar Interbody Fusion (PLIF) approach also

demonstrated the large cage size is significantly associated

with torsional stability [18]. Consistent with our modelling

results, a previous study illustrated that TLIF with bilateral

PSF improves fusion construct stability and decreases

posterior instrumentation stress [19]. We further demonstrated

that XLIF with bilateral and unilateral PSF can achieve similar

post-operative stability but may be subjected to variable facet

orientation. This interesting preliminary finding should be

investigated using cadaveric studies or clinical evidence to

further understand the underlying mechanisms of the unilateral

fixation stability and the facet tropism.

IV. CONCLUSION

In conclusion, clinicians can adapt the lesser invasive,

economical unilateral PS approach with XLIF to achieve

desired post-operative lumbar stability, while keeping the

contralateral side still available in case of future revision

surgery. Facet tropism seems to play an important role in

selecting the side of operation for unilateral fixation to reduce

facet joint strains, thus should be considered during pre-

operative planning.

ACKNOWLEDGMENT

The authors would like to thank Mr Jalil Jalali from the

Munich School of BioEngineering, TUM for his help in

model reconstruction in Geomagic and simulation in Ansys.

Dr. Ashish D Diwan acts as a paid consultant to Nuvasive Inc

for educational purposes and his institution receives an

educational grant from Nuvasive Inc. No funds were provided

for this research work from Nuvasive Inc.

Figure 4. Strain pattern in the model due to axial compression from the upper boundary (unit: mm/mm). The results were shown from the anterior view

of the spine, and the side of the fixation is indicated consistent with the anatomical orientation. XLIF reduced the max facet joint strain compared with

TLIF with bilateral or unilateral fixations in all cases. With unilateral fixation on the side with smaller facet joint angulation, the joint strain is comparable

with bilateral PSF. However, for the unilateral fixation on the side with larger facet joint angulation, or for the unilateral fixations using TLIF, the max

joint strains were significantly increased.

Figure 3. Stress pattern in the model due to axial compression from the upper boundary (unit: MPa). Maximum stress of the system was located on the

rods. The results were shown from the anterior view of the spine, and the side of the fixation is indicated consistent with the anatomical orientation.

XLIF reduced the max rod stress in comparison with TLIF with bilateral or unilateral fi xations in all cases. Unilateral fixations with XLIF did not

increase but slightly decreased the max rod stress comparing with bilateral fixation.

1889

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Full-text available

Nov 2021

Study Design Retrospective clinical case series. Objectives To investigate the risk factors for intraoperative endplate violations and delayed cage subsidence after oblique lateral interbody fusion (OLIF) surgery. Secondly, to examine whether low Hounsfield unit (HU) values at different regions of the endplate are associated with intraoperative endplate violation or delayed cage subsidence. Methods 61 patients (aged 65.1 ± 9.5 years; 107 segments) who underwent OLIF with or without posterior instrumentation from May 2015 to April 2019 were retrospectively studied. Intraoperative endplate violation was measured on sagittal reconstructed computerized tomography (CT) images immediate postoperatively, while delayed cage subsidence was evaluated using lateral radiographs and defined at 1-month follow-up or later. Demographic information and clinical parameters such as age, body mass index, bone mineral density, number of surgical levels, cage dimension, disc height restoration, visual analogue scale (VAS), and HU at different regions of the endplate were obtained. Results Total postoperative cage subsidence was identified in 45 surgical levels (42.0%) in 26 patients (42.6%) up till postoperative 1-year follow-up. Low HU value at the ipsilateral epiphyseal ring was an independent risk factor for intraoperative endplate violation ( P = .008) with a cut-off value of 326.21 HUs. Low HU values at the central endplate had a significant correlation with delayed cage subsidence in stand-alone cases ( P = .013) with a cut-off value of 296.42 HUs. VAS scores were not different at 1 week postoperatively in cases with or without intraoperative endplate violation (3.12 ± .73 vs 2.89 ± .72, P = .166) and showed no difference at 1 year with or without delayed cage subsidence (1.95 ± .60 vs 2.26 ± .85, P = .173). Conclusions Intraoperative endplate violation and delayed cage subsidence are not uncommon with OLIF surgery. HUs of the endplate are good predictors for intraoperative endplate violation and cage subsidence since they can represent the regional bone quality of the endplate in contact with the implant. VAS improvements were not affected by intraoperative endplate violation or delayed cage subsidence at 1-year follow-up. Level of Evidence Level III.

The Evolution of Lateral Lumbar Interbody Fusion: A Journey from Past to Present

Article

Full-text available

Feb 2024
MED LITH

Lumbar interbody fusion procedures have seen a significant evolution over the years, with various approaches being developed to address spinal pathologies and instability, including posterior lumbar interbody fusion (PLIF), transforaminal lumbar interbody fusion (TLIF), anterior lumbar interbody fusion (ALIF), and lateral lumbar interbody fusion (LLIF). LLIF, a pivotal technique in the field, initially emerged as extreme/direct lateral interbody fusion (XLIF/DLIF) before the development of oblique lumbar interbody fusion (OLIF). To ensure comprehensive circumferential stability, LLIF procedures are often combined with posterior stabilization (PS) using pedicle screws. However, achieving this required repositioning of the patient during the surgical procedure. The advent of single-position surgery (SPS) has revolutionized the procedure by eliminating the need for patient repositioning. With SPS, LLIF along with PS can be performed either in the lateral or prone position, resulting in significantly reduced operative time. Ongoing research endeavors are dedicated to further enhancing LLIF procedures making them even safer and easier. Notably, the integration of robotic technology into SPS has emerged as a game changer, simplifying surgical processes and positioning itself as a vital asset for the future of spinal fusion surgery. This literature review aims to provide a succinct summary of the evolutionary trajectory of lumbar interbody fusion techniques, with a specific emphasis on its recent advancements.

MISS innovations: Approaches, predictive outcomes and risk avoidance

Book

Full-text available

Feb 2023

The discipline of spine surgery is changing dramatically thanks to innovations in surgical technology, big data analytics, improvement of AI/ML capabilities, and diagnostic standardization. It is now possible to transform classical surgical methods of treatment into minimally invasive spine surgeries (MISS). In this rapidly changing environment the community needs to consider all new evidence for and against these MISS innovations. Which MISS have been able to prove their benefits, and to whom? Are we seeing warning signs around certain procedures or for patients with certain risk factors? With computational advancements in AI/ML technologies and big data analytics it is becoming possible to provide the necessary evidence to optimize procedures and patient specific treatment paths. The pain and disability outcomes for MISS treatments vary from patient to patient and procedure to procedure. Failed back surgery syndrome is highly prevalent, and possibly preventable. Comparisons between surgical procedures and patient characteristics will help the spine surgery community improve the treatment experience for spine patients and surgeons alike. The goal of this special collection is to optimize MISS procedures for various spinal diseases by: 1. Evaluation of the types of MISS techniques for degenerative spine diseases, spine trauma and primary spinal tumors. 2. Analysis of short- and long-term results of MISS vs open treatments for degenerative spine diseases, spinal trauma and primary spinal cord tumors 3. Situational optimization of procedure selection 4. Improvement of prognostic prediction on a patient specific basis using data analytics, AL/ML This Research Topic welcomes reviews of minimally invasive spine surgical techniques with/without meta-analysis, editorials, short communications, and original studies covering topics related to: • Minimally invasive spine surgery • New procedures showing short term efficacy results • Predicting results • Surgical selection • Comparative analysis • Complications • Function restoration • Revision surgery

A biomechanical comparison of posterior fixation approaches in lumbar fusion using computed tomography based lumbosacral spine modelling

Article

Jan 2023

Extreme lateral interbody fusion (XLIF) may be performed with a standalone interbody cage, or with the addition of unilateral or bilateral pedicle screws; however, decisions regarding supplemental fixation are predominantly based on clinical indicators. This study examines the impact of posterior supplemental fixation on facet micromotions, cage loads and load-patterns at adjacent levels in a L4-L5 XLIF at early and late fusion stages. CT data from an asymptomatic subject were segmented into anatomical regions and digitally stitched into a surface mesh of the lumbosacral spine (L1-S1). The interbody cage and posterior instrumentation (unilateral and bilateral) were inserted at L4-L5. The volumetric mesh was imported into finite element software for pre-processing, running nonlinear static solves and post-processing. Loads and micromotions at the index-level facets reduced commensurately with the extent of posterior fixation accompanying the XLIF, while load-pattern changes observed at adjacent facets may be anatomically dependent. In flexion at partial fusion, compressive stress on the cage reduced by 54% and 72% in unilateral and bilateral models respectively; in extension the reductions were 58% and 75% compared to standalone XLIF. A similar pattern was observed at full fusion. Unilateral fixation provided similar stability compared to bilateral, however there was a reduction in cage stress-risers with the bilateral instrumentation. No changes were found at adjacent discs. Posterior supplemental fixation alters biomechanics at the index and adjacent levels in a manner that warrants consideration alongside clinical information. Unilateral instrumentation is a more efficient option where the stability requirements and subsidence risk are not excessive.

Comparative analysis of the results using direct lateral interbody spondilodesis and transforaminal lumbar interbody spondilodesis in patients with degenerative diseases of the lumbar spine

Article

Full-text available

Sep 2021

Introduction Various spondylodesis techniques are used in patients with degenerative diseases of the lumbar spine, but the benefits of these techniques have not been proven. Objective of the study was to assess the effect of the type of fusion on the incidence of implant instability and related revision surgeries. Material and Methods This monocentric prospective study included 133 patients with degenerative stenosis of the lumbar spine and confirmed instability of spinal motion segments. Patients underwent transforaminal lumbar interbody fusion (TLIF) with a single cage or direct lateral interbody fusion (DLIF) using standard-sized cages. The conventional open technique was used to supplement TLIF with pedicle screws while percutaneous screw placement was applied in patients treated with DLIF. The duration of follow-up was 18 months. Fisher's exact test was used to assess differences in the incidence of fixator instability based on MSCT and revision interventions. Logistic regression was used to assess the association between potential risk factors and complication rates. Results The use of DLIF detected by MSCT (32.9 vs 3.6%, p < 0.0001) resulted in a significant reduction in the incidence of screw instability and associated revision interventions (11.8 vs 0%, p = 0.0122). The results of logistic regression, taking into account factors such as bone density and the number of levels at which spondylodesis was performed, confirm the relationship between the reduced incidence of complications and the use of DLIF technology. Conclusion Using DLIF instead of TLIF in patients with degenerative stenosis at the lumbar spine level can lead to a significant reduction in the frequency of screw instability and associated revision surgeries.

The Relationship of Facet Joint Orientation and Tropism with Lumbar Disc Herniation and Degenerative Spondylolisthesis in the Lower Lumbar Spine

Article

Full-text available

Oct 2018

Study design: Retrospective study. Purpose: This study aimed to clarify the relationship of both facet tropism (FT) and the sagittally aligned facet (SAF) joint with lumbar disc herniation (LDH) and degenerative spondylolisthesis (DS). Overview of literature: Despite several studies conducted, there is no consensus on the association of the SAF joint and FT with DH and DS. Methods: Between June 2015 and December 2017, magnetic resonance imaging scans of 250 consecutive patients who underwent surgery for LDH and DS were analyzed. The facet angles at all the lower lumbar levels were calculated, and SAF and FT were noted. The relationship between the side of disc herniation and that of the SAF joint were also determined. Statistical analysis was performed, and the relation of SAF and FT to LDH and DS was noted. Results: We observed a positive relationship between SAF and LDH at L4-5 and L5-S1 with a p-value of 0.02 (<0.05). FT demonstrated a positive association with LDH at L4-5 (p=0.047) but not at L3-4 or L5-S1. SAF demonstrated a positive relationship with DS at L3-4 (p<0.001) but not at L3-4 or L5-S1. FT demonstrated a significant relation with DS at L4-5 (p<0.001), whereas no positive association was observed at L3-4 and L5-S1. Conclusions: The L4-5 level demonstrated a significant association with SAF and FT in LDH and DS. Moreover, SAF at L5-S1 demonstrated a positive association with LDH. These findings provide useful information for future longitudinal studies to elucidate the possible causes for such phenomena.

Association of facet tropism and orientation with lumbar disc herniation in young patients

Article

Full-text available

Feb 2018

Facet tropism and orientation are thought to be associated with lumbar disc herniation (LDH), but the relationship is not well established. Moreover, the effect of facet joint on LDH has not been outlined in young patients. The objective of this study was to investigate the associations of facet joint tropism and orientation with LDH in young patients (18–35 years) by computed tomography (CT). Fifty-three patients with LDH and 129 with neither LDH nor low back pain (18–35 years) were included in this study. The facet joint angles were measured for each facet joint by CT as per the method described by Noren et al. We defined facet tropism as a bilateral angle difference > 5°. Young cases with neither LDH nor low back pain were used as the control group. The results showed that LDH was significantly associated with more coronal facet joint orientation at L1–2 (p = 0.009), L2–3 (p = 0.004), and L3–4 (p = 0.004). No association was established between facet tropism and LDH. This study revealed that facet joint orientation was associated with LDH in young patients (18–35 years); they were more of coronal facing at upper levels. Also, the facet tropism was not associated with LDH.

Global, regional, and national incidence, prevalence, and years lived with disability for 328 diseases and injuries for 195 countries, 1990–2016: a systematic analysis for the Global Burden of Disease Study 2016

Article

Full-text available

Sep 2017

Background: As mortality rates decline, life expectancy increases, and populations age, non-fatal outcomes of diseases and injuries are becoming a larger component of the global burden of disease. The Global Burden of Diseases, Injuries, and Risk Factors Study 2016 (GBD 2016) provides a comprehensive assessment of prevalence, incidence, and years lived with disability (YLDs) for 328 causes in 195 countries and territories from 1990 to 2016. Methods: We estimated prevalence and incidence for 328 diseases and injuries and 2982 sequelae, their non-fatal consequences. We used DisMod-MR 2.1, a Bayesian meta-regression tool, as the main method of estimation, ensuring consistency between incidence, prevalence, remission, and cause of death rates for each condition. For some causes, we used alternative modelling strategies if incidence or prevalence needed to be derived from other data. YLDs were estimated as the product of prevalence and a disability weight for all mutually exclusive sequelae, corrected for comorbidity and aggregated to cause level. We updated the Socio-demographic Index (SDI), a summary indicator of income per capita, years of schooling, and total fertility rate. GBD 2016 complies with the Guidelines for Accurate and Transparent Health Estimates Reporting (GATHER). Findings: Globally, low back pain, migraine, age-related and other hearing loss, iron-deficiency anaemia, and major depressive disorder were the five leading causes of YLDs in 2016, contributing 57·6 million (95% uncertainty interval [UI] 40·8–75·9 million [7·2%, 6·0–8·3]), 45·1 million (29·0–62·8 million [5·6%, 4·0–7·2]), 36·3 million (25·3–50·9 million [4·5%, 3·8–5·3]), 34·7 million (23·0–49·6 million [4·3%, 3·5–5·2]), and 34·1 million (23·5–46·0 million [4·2%, 3·2–5·3]) of total YLDs, respectively. Age-standardised rates of YLDs for all causes combined decreased between 1990 and 2016 by 2·7% (95% UI 2·3–3·1). Despite mostly stagnant age-standardised rates, the absolute number of YLDs from non-communicable diseases has been growing rapidly across all SDI quintiles, partly because of population growth, but also the ageing of populations. The largest absolute increases in total numbers of YLDs globally were between the ages of 40 and 69 years. Age-standardised YLD rates for all conditions combined were 10·4% (95% UI 9·0–11·8) higher in women than in men. Iron-deficiency anaemia, migraine, Alzheimer's disease and other dementias, major depressive disorder, anxiety, and all musculoskeletal disorders apart from gout were the main conditions contributing to higher YLD rates in women. Men had higher age-standardised rates of substance use disorders, diabetes, cardiovascular diseases, cancers, and all injuries apart from sexual violence. Globally, we noted much less geographical variation in disability than has been documented for premature mortality. In 2016, there was a less than two times difference in age-standardised YLD rates for all causes between the location with the lowest rate (China, 9201 YLDs per 100 000, 95% UI 6862–11943) and highest rate (Yemen, 14 774 YLDs per 100 000, 11 018–19 228). Interpretation: The decrease in death rates since 1990 for most causes has not been matched by a similar decline in age-standardised YLD rates. For many large causes, YLD rates have either been stagnant or have increased for some causes, such as diabetes. As populations are ageing, and the prevalence of disabling disease generally increases steeply with age, health systems will face increasing demand for services that are generally costlier than the interventions that have led to declines in mortality in childhood or for the major causes of mortality in adults. Up-to-date information about the trends of disease and how this varies between countries is essential to plan for an adequate health-system response.

Unilateral versus bilateral pedicle screw fixation with posterior lumbar interbody fusion for lumbar degenerative diseases

Article

Full-text available

May 2017

Background Both unilateral pedicle screw fixation with posterior lumbar interbody fusion (PLIF) and bilateral pedicle screw fixation with PLIF are used to treat lumbar degenerative diseases (LDD). However, which one is a better treatment for LDD remains considerable controversy. Therefore, the focus of this meta-analysis was to assess the merits and shortcomings of efficacy of these 2 surgical procedures for LDD. Methods An extensive search of literature was performed in Pubmed/MEDLINE, Embase, CNKI, and WANFANG databases on unilateral versus bilateral pedicle screw fixation with PLIF fusion for LDD, from January 2007 to January 2017 and language was restricted to Chinese or English. The following variables were extracted: blood loss, operation time, length of hospital stay, Japanese Orthopedic Association (JOA) scores, visual analog scale (VAS) and Oswestry disability index (ODI) scores, fusion rate, total complications, infection, dural injury, and nerve injury. Data analysis was conducted with RevMan 5.3 and STATA 12.0. Results A total of 11 studies containing 844 patients were included in our study. The results showed that unilateral is better than bilateral pedicle screw fixation with PLIF in blood loss (P < .00001), operation time (P < .00001), the length of hospital stay (P = .003), and the final follow-up ODI scores (P = .04). However, there are no significant differences in JOA, VAS, and preoperative ODI scores. There are also no significant differences in fusion rate and complications (all P > .05). Conclusion Based on our meta-analysis, our results suggest that both unilateral pedicle screw fixation with PLIF and bilateral pedicle screw fixation with PLIF for LDD have effective results in clinical outcomes. Both 2 methods may result in clinical improvement and similar outcomes of fusion rate and complications; However, compared with bilateral fixation, unilateral fixation produces more satisfactory efficacy in the blood loss and the operation time.

Critical Values of Facet Joint Angulation and Tropism in the Development of Lumbar Degenerative Spondylolisthesis: An International, Large-Scale Multicenter Study by the AOSpine Asia Pacific Research Collaboration Consortium

Article

Full-text available

Oct 2015

Study design: An international, multicenter cross-sectional image-based study performed in 33 institutions in the Asia Pacific region. Objective: The study addressed the role of facet joint angulation and tropism in relation to L4-L5 degenerative spondylolisthesis (DS). Methods: The study included 349 patients (63% females; mean age: 61.8 years) with single-level DS; 82 had no L4-L5 DS (group A) and 267 had L4-L5 DS (group B). Axial computed tomography and magnetic resonance imaging were utilized to assess facet joint angulations and tropism (i.e., asymmetry between facet joint angulations) between groups. Results: There was a statistically significant difference between group A (left mean: 46.1 degrees; right mean: 48.2 degrees) and group B (left mean: 55.4 degrees; right mean: 57.5 degrees) in relation to bilateral L4-L5 facet joint angulations (p < 0.001). The mean bilateral angulation difference was 7.4 and 9.6 degrees in groups A and B, respectively (p = 0.025). A critical value of 58 degrees or greater significantly increased the likelihood of DS if unilateral (adjusted OR: 2.5; 95% CI: 1.2 to 5.5; p = 0.021) or bilateral facets (adjusted OR: 5.9; 95% CI: 2.7 to 13.2; p < 0.001) were involved. Facet joint tropism was found to be relevant between 16 and 24 degrees angulation difference (adjusted OR: 5.6; 95% CI: 1.2 to 26.1; p = 0.027). Conclusions: In one of the largest studies assessing facet joint orientation in patients with DS, greater sagittal facet joint angulation was associated with L4-L5 DS, with a critical value of 58 degrees or greater increasing the likelihood of the condition for unilateral and bilateral facet joint involvement. Specific facet joint tropism categories were noted to be associated with DS.

Comparison of Unilateral versus Bilateral Pedicle Screw Fixation in Transforaminal Lumbar Interbody Fusion for Single Level Lumbar Degenerative Diseases and Review of Literature

Article

Jul 2017
TURK NEUROSURG

Aim: There are some recognized treatment modalities in the literature for the treatment of lumbar degenerative diseases,which cause pain and avoidance of daily life activities for the patients.The most widely accepted algorithm in the literature is medical treatment,physical therapy and minimally invasive pain-relieving therapies,if necessary,followed by surgical interventions.The common procedure used in neurosurgery practice is the decompression of neural elements followed by fusion.It is reported in the literature that unilateral pedicle fixation and Transforaminal Lumbar Interbody Fusion(TLIF) procedure have many advantages compared to bilateral pedicle screw implementation(PSF).We examined the clinical and radiological follow-up and results of our patients undergoing fusion procedure by unilateral versus bilateral pedicle screw fixation along with TLIF. Material and methods: 54 patients were included in the study.33 patients were operated with bilateral PSF and TLIF and 21 had unilateral PSF and TLIF.The patients were evaluated preoperatively,on the postoperative 15th day,6th and 12th month, and at the time of last examination (38 months in average for all patients) using Visual Analogue Scale(VAS) and Oswestry Disability Index(ODI).Fusion rates were examined with direct X-ray films with flexion-extension dynamic views and 3D CT scan. Results: Operation times are shorter and blood loss is less in the unilateral PSF group.Fusion rates are similar in both groups with no statistical significance.For both groups significant clinical improvement was observed in the preoperative and postoperative scores. Conclusion: Unilateral PSF along with TLIF procedure is an effective option in selected patients.We need prospective randomized studies with higher number of patients and longer follow-up periods for more reliable results.

Unilateral Versus Bilateral Pedicle Screw Fixation in Transforaminal Lumbar Interbody Fusion: A Monocentric Study of 215 Patients With a Minimum of 4-Year Follow-up

Article

Jul 2016

Study design: A retrospective clinical study. Objective: This study sought to retrospectively compare the mid-term to long-term outcomes between unilateral pedicle screw (UPS) and bilateral pedicle screw (BPS) augmented transforaminal lumbar interbody fusion (TLIF) in lumbar degenerative diseases. Summary of background data: Recently, UPS fixation has been applied in TLIF, for its satisfactory clinical outcome, less implants and less invasiveness. However, only short-term outcome has been reported, the mid-term to long-term outcome has not been well characterized. Materials and methods: From June 2007 to February 2011, 215 of 348 consecutive patients suffering from lumbar degenerative diseases were operated in our hospital and accomplished a minimum of 4-year follow-up. These patients were divided into 2 groups according to the operative techniques: UPS group (n=109), and bilateral pedicle screw group (n=106). Operative time, blood loss, length of hospital stay, hospital bill, fusion status, and complications were recorded and analyzed statistically. Visual analog scale, Oswestry disability index, and Japanese Orthopaedic Association scores were used to assess the preoperative and postoperative pain and functional outcome. Results: The mean follow-up duration was 52.2 months. A significant decrease occurred in operative time, blood loss, and hospital bill in unilateral group, compared with bilateral group (P<0.05). The average postoperative visual analog scale, Oswestry disability index, and Japanese Orthopaedic Association scores improved significantly in each group than the preoperative counterparts (P<0.05); however, there were no significant difference between groups at any follow-up time point (P>0.05). No statistically difference was detected regarding fusion rate and complication rate between the 2 groups (P>0.05), except the cage migration rate (P<0.05). Conclusions: UPS fixation could achieve satisfactory clinical outcome similar to bilateral fixation in TLIF at a mid-term to long-term follow-up. To avoid cage migration, bullet-shaped cages should not be used in the unilateral group.

3D Slicer: A Platform for Subject-Specific Image Analysis, Visualization, and Clinical Support

Chapter

Jan 2014

3D Slicer is an open-source platform for the analysis and display of information derived from medical imaging and similar data sets. Such advanced software environments are in daily use by researchers and clinicians and in many nonmedical applications. 3D Slicer is unique through serving clinical users, multidisciplinary clinical research terms, and software architects within a single technology structure and user community. Functions such as interactive visualization, image registration, and model-based analysis are now being complemented by more advanced capabilities, most notably in neurological imaging and intervention. These functions, originally limited to offline use by technical factors, are integral to large scale, rapidly developing research studies, and they are being increasingly integrated into the management and delivery of care. This activity has been led by a community of basic, applied, and clinical scientists and engineers, from both academic and commercial perspectives. 3D Slicer, a free open-source software package, is based in this community; 3D Slicer provides a set of interactive tools and a stable platform that can quickly incorporate new analysis techniques and evolve to serve more sophisticated real-time applications while remaining compatible with the latest hardware and software generations of host computer systems.

Bilateral Pedicle Screw Fixation Provides Superior Biomechanical Stability in Transforaminal Lumbar Interbody Fusion: A Finite Element Study.

Article

Jun 2014

Background context: Transforaminal lumbar interbody fusion (TLIF) is increasingly popular for the surgical treatment of degenerative lumbar disease. The optimal construct for segmental stability remains unknown. Purpose: To compare the stability of fusion constructs using standard (C) and crescent-shaped (CC) polyetheretherketone TLIF cages with unilateral (UPS) or bilateral (BPS) posterior instrumentation. Study design: Five TLIF fusion constructs were compared using finite element (FE) analysis. Methods: A previously validated L3-L5 FE model was modified to simulate decompression and fusion at L4-L5. This model was used to analyze the biomechanics of various unilateral and bilateral TLIF constructs. The inferior surface of the L5 vertebra remained immobilized throughout the load simulation, and a bending moment of 10 Nm was applied on the L3 vertebra to recreate flexion, extension, lateral bending, and axial rotation. Various biomechanical parameters were evaluated for intact and implanted models in all loading planes. Results: All reconstructive conditions displayed decreased motion at L4-L5. Bilateral posterior fixation conferred greater stability when compared with unilateral fixation in left lateral bending. More than 50% of intact motion remained in the left lateral bending with unilateral posterior fixation compared with less than 10% when bilateral pedicle screw fixation was used. Posterior implant stresses for unilateral fixation were six times greater in flexion and up to four times greater in left lateral bending compared with bilateral fixation. No effects on segmental stability or posterior implant stresses were found. An obliquely-placed, single standard cage generated the lowest cage-end plate stress. Conclusions: Transforaminal lumbar interbody fusion augmentation with bilateral posterior fixation increases fusion construct stability and decreases posterior instrumentation stress. The shape or number of interbody implants does not appear to impact the segmental stability when bilateral pedicle screws are used. Increased posterior instrumentation stresses were observed in all loading modes with unilateral pedicle screw/rod fixation, which may theoretically accelerate implant loosening or increase the risk of construct failure.

The biomechanical influence of the facet joint orientation and the facet tropism in the lumbar spine

Article

Sep 2013

Facet joint orientation and facet tropism (FT) are presented as the potential anatomical predisposing factors for lumbar degenerative changes that may lead in turn to early degeneration and herniation of the corresponding disc or degenerative spondylolisthesis. However, no biomechanical study of this concept has been reported. To investigate the biomechanical influence of the facet orientation and FT on stress on the corresponding segment. Finite element analysis. Three models, F50, F55, and F60 were simulated with different facet joint orientations (50°, 55°, and 60° relative to coronal plane) at both L2-L3 facet joints. A FT model was also simulated to represent a 50° facet joint angle at the right side and a 60° facet joint angle at the left side in the L2-L3 segment. In each model, the intradiscal pressures were investigated under four pure moments and anterior shear force. Facet contact forces at the L2-L3 segment were also analyzed under extension and torsion moments and anterior shear force. This study was supported by 5000 CHF grant of 2011 AO Spine Research Korea fund. The authors of this study have no topic-specific potential conflicts of interest related to this study. The F50, F55, and F60 models did not differ in the intradiscal pressures generated under four pure moments: but under anterior shear force, the F60 and FT models showed increases of intradiscal pressure. The F50 model under extension and the F60 model under torsion each generated an increase in facet contact force. In all conditions tested, the FT model yielded the greatest increase of intradiscal pressure and facet contact force of all the models. The facet orientation per se did not increase disc stress or facet joint stress prominently at the corresponding level under four pure moments, but FT could make the corresponding segment more vulnerable to external moments or anterior shear force.

XLIF interbody cage reduces stress and strain of fixation in spinal reconstructive surgery in comparison with TLIF cage with bilateral or unilateral fixation: a computational analysis

Abstract

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