Stand-alone Lateral Lumbar Interbody Fusion Research Articles

Comparison of instrumented and stand-alone lateral lumbar interbody fusion for lumbar degenerative disease: a systematic review and meta-analysis

BackgroundBoth instrumented and stand-alone lateral lumbar interbody fusion (LLIF) have been widely used to treat lumbar degenerative disease. However, it remains controversial as whether posterior internal fixation is required when LLIF is performed. This meta-analysis aims to compare the radiographic and clinical results between instrumented and stand-alone LLIF.MethodsPubMed, EMBASE and Cochrane Collaboration Library up to March 2023 were searched for studies that compared instrumented and stand-alone LLIF in the treatment of lumbar degenerative disease. The following outcomes were extracted for comparison: interbody fusion rate, cage subsidence rate, reoperation rate, restoration of disc height, segmental lordosis, lumbar lordosis, visual analog scale (VAS) scores of low-back and leg pain and Oswestry Disability Index (ODI) scores.Results13 studies involving 1063 patients were included. The pooled results showed that instrumented LLIF had higher fusion rate (OR 2.09; 95% CI 1.16–3.75; P = 0.01), lower cage subsidence (OR 0.50; 95% CI 0.37–0.68; P < 0.001) and reoperation rate (OR 0.28; 95% CI 0.10–0.79; P = 0.02), and more restoration of disc height (MD 0.85; 95% CI 0.18–1.53; P = 0.01) than stand-alone LLIF. The ODI and VAS scores were similar between instrumented and stand-alone LLIF at the last follow-up.ConclusionsBased on this meta-analysis, instrumented LLIF is associated with higher rate of fusion, lower rate of cage subsidence and reoperation, and more restoration of disc height than stand-alone LLIF. For patients with high risk factors of cage subsidence, instrumented LLIF should be applied to reduce postoperative complications.

BIOMECHANICAL STUDY OF LATERAL LUMBAR INTERBODY FUSION VERSUS A POSTERIOR FIXATION WITH PEDICLE SCREWS AND RODS USING A HUMAN CADAVERIC MODEL

Lateral lumbar interbody fusion (LLIF) has biomechanical advantages due to the preservation of ligamentous structures (ALL/PLL), and optimal cage height afforded by the strength of the apophyseal ring. We compare the biomechanical motion stability of multiple levels LLIF (4 segments) utilising PEEK interbody 26mm cages to stand-alone cage placement and with supplemental posterior fixation with pedicle screw and rods.Six lumbar human cadaver specimens were stripped of the paraspinal musculature while preserving the discs, facet joints, and osteoligamentous structures and potted. Specimens were tested under 5 conditions: intact, posterior bilateral fixation (L1-L5) only, LLIF-only, LLIF with unilateral fixation and LLIF with bilateral fixation. Non-destructive testing was performed on a universal testing machine (MTS Systems Corp) to produce flexion-extension, lateral-bending, and axial rotation using customized jigs and a pulley system to define a non-constraining load follower. Three-dimensional spine motion was recorded using a motion device (Optotrak).Results are reported for the L3-L4 motion segment within the construct to allow comparison with previously published works of shorter constructs (1-2 segments). In all conditions, there was an observed decrease in ROM from intact in flexion/extension (31%-89% decrease), lateral bending (19%-78%), and axial rotation (37%-60%). At flexion/extension, the decreases were statistically significant (p&lt;0.007) except for stand-alone LLIF. LLIF+unilateral had similar decreases in all planes as the LLIF+bilateral condition. The observed ROM within the 4-level construct was similar to previously reported results in 1-2 levels for stand-alone LLIF and LLIF+bilateral.Surgeons may be concerned about the biomechanical stability of an approach utilizing stand-alone multilevel LLIF. Our results show that 4-level multilevel LLIF utilizing 26 mm cages demonstrated ROM comparable to short-segment LLIF. Stand-alone LLIF showed a decrease in ROM from the intact condition. The addition of posterior supplemental fixation resulted in an additional decrease in ROM. The results suggest that unilateral posterior fixation may be sufficient.

Changes in psoas and posterior paraspinal muscle morphology after standalone lateral lumbar interbody fusion: a quantitative MRI-based analysis.

Standalone lateral lumbar interbody fusion (SA-LLIF) without posterior instrumentation can be an alternative to 360° fusion in selected cases. This study aimed to investigate quantitative changes in psoas and paraspinal muscle morphology that occur on index levels after SA-LLIF. Patients undergoing single- or multi-level SA-LLIF at L2/3 to L4/5 who had preoperative and postoperative lumbar MRI scans, the latter performed between 3 and 18months after surgery for any reason, were retrospectively included. Muscle measurements were performed of the psoas and posterior paraspinal muscles (PPM; erector spinae and multifidus) on index levels using manual segmentation and an automated pixel intensity threshold method to differentiate muscle from fat signal. Changes in the total cross-sectional area (TCSA), the functional cross-sectional area (FCSA), and the percentage of fat infiltration (FI) of these muscles were assessed. A total of 67 patients (55.2% female, age 64.3 ± 10.6years, BMI 26.9 ± 5.0kg/m2) with 125 operated levels were included. Follow-up MRI scans were performed after an average of 8.7 ± 4.6months, primarily for low back pain. Psoas muscle parameters did not change significantly, irrespective of the approach side. Among PPM parameters, the mean TCSA at L4/5 (+ 4.8 ± 12.4%; p = 0.013), and mean FI at L3/4 (+ 3.1 ± 6.5%; p = 0.002) and L4/5 (+ 3.0 ± 7.0%; p = 0.002) significantly increased. Our study demonstrated that SA-LLIF did not alter psoas muscle morphology, underlining its minimally invasive nature. However, FI of PPM significantly increased over time despite the lack of direct tissue damage to posterior structures, suggesting a pain-mediated response and/or the result of segmental immobilization.

Long-Term Durability of Stand-Alone Lateral Lumbar Interbody Fusion.

The long-term durability of stand-alone lateral lumbar interbody fusion (LLIF) remains unknown. To evaluate whether early patient-reported outcome measures after stand-alone LLIF are sustained on long-term follow-up. One hundred and twenty-six patients who underwent stand-alone LLIF between 2009 and 2017 were included in this study. Patient-reported outcome measures included the Oswestry Disability Index (ODI), EuroQOL-5D (EQ-5D), and visual analog score (VAS) scores. Durable outcomes were defined as scores showing a significant improvement between preoperative and 6-week scores without demonstrating any significant decline at future time points. A repeated measures analysis was conducted using generalized estimating equations (model) to assess the outcome across different postoperative time points, including 6 weeks, 1 year, 2 years, and 5 years. ODI scores showed durable improvement at 5-year follow-up, with scores improving from 46.9 to 38.5 ( P = .001). Improvements in EQ-5D showed similar durability up to 5 years, improving from 0.48 to 0.65 ( P = .03). VAS scores also demonstrated significant improvements postoperatively that were durable at 2-year follow-up, improving from 7.0 to 4.6 ( P < .0001). Patients undergoing stand-alone LLIF were found to have significant improvements in ODI and EQ-5D at 6-week follow-up that remained durable up to 5 years postoperatively. VAS scores were found to be significantly improved at 6 weeks and up to 2 years postoperatively but failed to reach significance at 5 years. These findings demonstrate that patients undergoing stand-alone LLIF show significant improvement in overall disability after surgery that remains durable at long-term follow-up.

Impact of cage position on biomechanical performance of stand-alone lateral lumbar interbody fusion: a finite element analysis

BackgroundThis study aimed to compare the biomechanical performance of various cage positions in stand-alone lateral lumbar interbody fusion(SA LLIF).MethodsAn intact finite element model of the L3-L5 was reconstructed. The model was verified and analyzed. Through changing the position of the cage, SA LLIF was established in four directions: anterior placement(AP), middle placement(MP), posterior placement(PP), oblique placement(OP). A 400 N vertical axial pre-load was imposed on the superior surface of L3 and a 10 N/m moment was applied on the L3 superior surface along the radial direction to simulate movements of flexion, extension, lateral bending, and axial rotation. Various biomechanical parameters were evaluated for intact and implanted models in all loading conditions, including the range of motion (ROM) and maximum stress.ResultsIn the SA LLIF models, the ROM of L4-5 was reduced by 84.21–89.03% in flexion, 72.64–82.26% in extension, 92.5-95.85% in right and left lateral bending, and 87.22–92.77% in right and left axial rotation, respectively. Meanwhile, ROM of L3-4 was mildly increased by an average of 9.6% in all motion directions. Almost all stress peaks were increased after SA LLIF, including adjacent disc, facet joints, and endplates. MP had lower stress peaks of cage and endplates in most motion modes. In terms of the stress on facet joints and disc of the cephalad segment, MP had the smallest increment.ConclusionIn our study, SA LLIF risked accelerating the adjacent segment degeneration. The cage position had an influence on the distribution of endplate stress and the magnitude of facet joint stress. Compared with other positions, MP had the slightest effect on the stress in the adjacent facet joints. Meanwhile, MP seems to play an important role in reducing the risk of cage subsidence.

Fusion assessment in standalone lateral lumbar interbody fusion: 3D-printed titanium versus polyetheretherketone (PEEK) cages.

BackgroundCompare fusion at two independent timepoints (early and late) between 3D-printed titanium (Ti) and polyetheretherketone (PEEK) cages in patients undergoing standalone lateral lumbar interbody fusion (SA-LLIF). We hypothesized that 3D-printed Ti cages show higher fusion rates at an early timepoint compared to PEEK.MethodsA retrospective study of patients undergoing SA-LLIF with 3D-printed Ti cages and PEEK cages between 11/2016 and 01/2020 at a single academic institution was done. Fusion was assessed for each treated level using multiplanar reconstructed computed tomography (CT) scans. Presence of fully bridged interbody trabecular bone or continuous bone centered in the cage was considered as fusion.ResultsIn total, 91 patients (136 levels) were included in the final analysis, 49 patients (72 levels) in the early group and 42 patients (64 levels) in the late group. CT scans were performed on average 8.2±1.8 months postoperatively for the early group and 18.9±7.7 months for the late group. In the early group, fusion was significantly higher for 3D-printed Ti cages compared to PEEK cages (95.8% versus 62.5%; P=0.002), whereas in the late group no significant difference was seen (94.7% versus 80.0%; P=0.258).ConclusionsIn SA-LLIF, porous 3D-printed Ti cages showed significantly higher fusion rates at an early timepoint compared to PEEK. However, the difference in fusion rates between 3D-printed Ti cages and PEEK cages was found not to be significantly different at a later timepoint in another patient group. This might support the assumption that 3D-printed Ti cages with a porous architecture are more osteoconductive compared to PEEK and tend to fuse earlier.

The predictive value of a novel site-specific MRI-based bone quality assessment, endplate bone quality (EBQ), for severe cage subsidence among patients undergoing standalone lateral lumbar interbody fusion

BACKGROUND CONTEXTStudies have shown that site-specific bone density measurements had more predictive value for complications than standard whole-region measurements. Recently, MRI-based assessments of vertebral bone quality (VBQ) were introduced. However, there have been few studies that investigate the association between site-specific MRI bone assessment and osteoporosis-related complications in patients undergoing lumbar interbody fusion. In this work, we created a novel site-specific MRI-based assessment of the endplate bone quality (EBQ) and assessed its predictive value for severe cage subsidence following standalone lateral lumbar interbody fusion (SA-LLIF). PURPOSETo investigate the predictive value of a novel MRI-based bone assessment for severe cage subsidence after SA-LLIF. STUDY DESIGN/SETTINGRetrospective cohort study. PATIENT SAMPLEPatients who underwent SA-LLIF from 2008 to 2019 at a single, academic institution with available preoperative lumbar CT and T1-weighted MRIs. OUTCOME MEASURESAssociation between EBQ and severe subsidence after SA-LLIF. METHODSWe retrospectively reviewed the records of SA-LLIF patients treated between 2008 and 2019. EBQ was measured using preoperative non-contrast T1-weighted MRIs of the lumbar spine. EBQ was defined as the average value of signal intensity of both endplates divided by that of the cerebrospinal fluid space at the level of L3. Bivariate and multivariable analyses with generalized linear mixed models were performed and set binary severe subsidence as the outcome. RESULTSTwo hundred five levels in 89 patients were included. Fifty levels (24.4%) demonstrated severe subsidence. Bone mineral density measured by quantitative computed tomography was significantly lower in the subsidence group. Both VBQ and EBQ were significantly higher in the subsidence group. The EBQ plus Modic change (MC) model demonstrated that the effect of EBQ was independent of MC. In multivariate analyses adjusted with QCT-vBMD, EBQ showed a significant association with cage subsidence whereas VBQ only showed a marginal trend. The EBQ-based prediction model for severe subsidence showed better goodness of fit compared to the VBQ-based model. CONCLUSIONSHigh EBQ was an independent factor for severe cage subsidence after SA-LLIF and the EBQ-based model showed better goodness of fit compared to VBQ- or MC-based models. EBQ assessment before SA-LLIF may provide insight into a patient's risk for severe subsidence.

When to Consider Stand-Alone Lateral Lumbar Interbody Fusion: Is There a Role for a Comeback With New Implants?

To perform a comprehensive review of the literature about the role of stand-alone lateral lumbar interbody fusion (LLIF). A MEDLINE review was conducted including studies about stand-alone LLIF for any condition. The opinions of the authors were also considered. Studies that included biomechanical, cadaveric, or clinical aspects of stand-alone cages were revised to obtain data about the pros, cons, and limitations of the technique. Comparative studies with 360° (lateral + posterior) fusions were also analyzed. A total of 36 studies were identified. After reviewing the abstracts, 18 full articles of interest for the objective of this review were analyzed. Recommendations based on the literature were made. Although most of the recommendations in the literature were about augmentation with pedicle screws, there may be a role for stand-alone LLIF in some particular cases. Specific technical aspects should be considered to reduce the failure rate. Although there might be some specific indications for stand-alone LLIF, it should be considered an exception rather than the rule.

The predictive value of psoas and paraspinal muscle parameters measured on MRI for severe cage subsidence after standalone lateral lumbar interbody fusion

BACKGROUND CONTEXTThe effect of psoas and paraspinal muscle parameters on cage subsidence after minimally invasive techniques, such as standalone lateral lumbar interbody fusion (SA-LLIF), is unknown. PURPOSEThis study aimed to determine whether the functional cross-sectional area (FCSA) of psoas and lumbar spine extensor muscles (multifidus and erector spinae), and psoas FCSA normalized to the vertebral body area (FCSA/VBA) differ among levels with severe cage subsidence after SA-LLIF when compared to levels without severe cage subsidence. STUDY DESIGNRetrospective single center cohort study. PATIENT SAMPLEPatients who underwent SA-LLIF between 2008 and 2020 for degenerative conditions using exclusively polyetheretherketone (PEEK) cages, had a lumbar magnetic resonance imaging (MRI) scan within 12 months, a lumbar computed tomography (CT) scan within 6 months prior to surgery, and a postoperative clinical and radiographic follow-up at a minimum of 6 months were included. OUTCOME MEASURESSevere cage subsidence. METHODSMRI measurements included psoas and combined multifidus and erector spinae (paraspinal) FCSA and FCSA/VBA at the L3-L5 pedicles. Following manual segmentation of muscles on axial T2-weighted images using ITK-SNAP (version 3.8.0), the FCSA was calculated using a custom written program on Matlab (version R2019a, The MathWorks, Inc.) that used an automated pixel intensity threshold method to differentiate between fat and muscle. Mean volumetric bone mineral density (vBMD) at L1/2 was measured by quantitative CT. The primary endpoint was severe cage subsidence per level according to the classification by Marchi et al. Multivariable logistic regression analysis was performed using generalized linear mixed models. All analyses were stratified by biological sex. RESULTS95 patients (45.3% female) with a total of 188 operated levels were included in the analysis. The patient population was 92.6% Caucasian with a median age at surgery of 65 years. Overall subsidence (Grades 0-III) was 49.5% (53/107 levels) in men versus 58.0% (47/81 levels) in women (p=.302), and severe subsidence (Grades II-III) was 22.4% (24/107 levels) in men versus 25.9% (21/81 levels) in women (p=.608). In men, median psoas FCSA and psoas FCSA/VBA at L3 and L4 were significantly greater in the severe subsidence group when compared to the non-severe subsidence group. No such difference was observed in women. Paraspinal muscle parameters did not differ significantly between non-severe and severe subsidence groups for both sexes. In the multivariable logistic regression analysis with adjustments for vBMD and cage length, psoas FCSA at L3 (OR 1.002; p=.020) and psoas FCSA/VBA at L3 (OR 8.655; p=.029) and L4 (OR 4.273; p=.043) were found to be independent risk factors for severe cage subsidence in men. CONCLUSIONSOur study demonstrated that greater psoas FCSA at L3 and psoas FCSA/VBA at L3 and L4 were independent risk factors for severe cage subsidence in men after SA-LLIF with PEEK cages. The higher compressive forces the psoas exerts on lumbar segments as a potential stabilizer might explain these findings. Additional pedicle screw fixation might be warranted in these patients to avoid severe cage subsidence.

Does preoperative morphology of multifidus influence the surgical outcomes of stand-alone lateral lumbar interbody fusion for lumbar spondylolisthesis?

ObjectivesTo investigate whether the preoperative morphology of multifidus influences the surgical outcomes of stand-alone lateral lumbar interbody fusion (LLIF) for lumbar spondylolisthesis. Patients and methodsFifty-eight patients with lumbar spondylolisthesis who underwent single-level, stand-alone LLIF at the L4–5 level were included and followed up for at least 12 months. Preoperative axial cross-sectional area (CSA) and fat infiltration rate (FIR) of multifidus on MRI scans were measured using the ImageJ software. The CSA ratio and FIR were calculated and classified into three grades. Preoperative and final visual analogue scale (VAS) scores for back pain and leg pain, Oswestry Disability Index (ODI) scores were recorded. Cage subsidence and fusion were also evaluated at the final follow-up. Correlations between VAS scores, ODI scores, obvious cage subsidence and fusion rate with the CSA ratio and FIR were analyzed. ResultsThere were significant correlations between preoperative and final VAS scores for back pain and ODI scores with the CSA ratio and FIR. There was an overall trend towards improvements in back pain and lumbar function in patients with superior morphology of multifidus. In addition, obvious cage subsidence was found to be associated with lower preoperative CSA ratios and higher FIR, whereas fusion rate was only correlated with FIR. ConclusionsThe preoperative morphology of multifidus influenced the surgical outcomes of stand-alone LLIF for lumbar spondylolisthesis. Patients with superior morphology of multifidus showed better outcomes following stand-alone LLIF.

Computed Tomography Hounsfield Units as a Predictor of Reoperation and Graft Subsidence After Standalone and Multilevel Lateral Lumbar Interbody Fusion

Standalone single and multilevel lateral lumbar interbody fusion (LLIF) have been increasingly applied to treat degenerative spinal conditions in a less invasive fashion. Graft subsidence following LLIF is a known complication and has been associated with poor bone mineral density (BMD). Previous research has demonstrated the utility of computed tomography (CT) Hounsfield units (HUs) as a surrogate for BMD. In the present study, we investigated the relationship between the CT HUs and subsidence and reoperation after standalone and multilevel LLIF. A prospectively maintained single-institution database was retrospectively reviewed for LLIF patients from 2017 to 2020, including single and multilevel standalone cases with and without supplemental posterior fixation. Data on demographics, graft parameters, BMD determined by dual-energy x-ray absorptiometry, preoperative mean segmental CT HUs, and postoperative subsidence and reoperation were collected. We used 36-in. standing radiographs to measure the preoperative global sagittal alignment and disc height and subsidence at last follow-up. Subsidence was classified using the Marchi grading system corresponding to disc height loss: grade 0, 0%-24%; grade I, 25%-49%; grade II, 50%-74%; and grade III, 75%-100%. A total of 89 LLIF patients had met the study criteria, with a mean follow-up of 19.9 ± 13.9 months. Of the 54 patients who had undergone single-level LLIF, the mean segmental HUs were 152.0 ± 8.7 for 39 patients with grade 0 subsidence, 136.7 ± 10.4 for 9 with grade I subsidence, 133.9 ± 23.1 for 3 with grade II subsidence, and 119.9 ± 30.9 for 3 with grade III subsidence (P= 0.032). Of the 96 instrumented levels in the 35 patients who had undergone multilevel LLIF, 85, 9, 1, and 1 level had had grade 0, grade I, grade II, and grade III subsidence, with no differences in the HU levels. On multivariate logistic regression, increased CT HU levels were independently associated with a decreased risk of reoperation after both single-level and multilevel LLIF (odds ratio, 0.98; 95% confidence interval, 0.97-0.99; P= 0.044; and odds ratio, 0.97; 95% confidence interval, 0.94-0.99; P= 0.017, respectively). Overall, the BMD determined using dual-energy x-ray absorptiometry was not associated with graft subsidence or reoperation. Using a receiver operating characteristic curve to separate the patients who had and had not required reoperation, the threshold HU level determined for single-level and multilevel LLIF was 131.4 (sensitivity, 0.62; specificity 0.65) and 131.0 (sensitivity, 0.67; specificity, 0.63), respectively. Lower CT HUs were independently associated with an increased risk of graft subsidence after single-level LLIF. In addition, lower CT HUs significantly increased the risk of reoperation after both single and multilevel LLIF with a critical threshold of 131 HUs. The determination of the preoperative CT HUs might provide a more robust gauge of local bone quality and the likelihood of graft subsidence requiring reoperation following LLIF than overall BMD.

Early Outcomes of Three-Dimensional–Printed Porous Titanium versus Polyetheretherketone Cage Implantation for Stand-Alone Lateral Lumbar Interbody Fusion in the Treatment of Symptomatic Adjacent Segment Degeneration

To compare outcomes of three-dimensional-printed porous titanium (Ti) versus polyetheretherketone (PEEK) cage implantation for stand-alone lateral lumbar interbody fusion (SA-LLIF) in treatment of symptomatic adjacent segment degeneration. Between October 2016 and July 2020, 44 patients (59 levels) underwent stand-alone lateral lumbar interbody fusion with Ti or PEEK cages. The primary outcome was cage subsidence. Secondary outcomes included revision and/or recommendations for revision surgery, back and/or leg pain severity, changes in disc and/or foraminal height, and global and/or segmental lumbar lordosis. The study included 44 patients (21 females) with a mean age at surgery of 61.8 ± 11.5 years, mean radiological follow-up of 12.5 ± 8.2 months, and mean clinical follow-up of 11.0 ± 7.1 months. Overall subsidence rate was significantly less in the Ti versus PEEK group (20% vs. 58.8%, P= 0.004). Revision was recommended to none of the patients in the Ti group and 3 patients in the PEEK group (P= 0.239). Patients in the Ti group showed significantly better improvement in back pain numeric rating scale score (P= 0.001). Disc height (P < 0.001) and foraminal height restoration (P= 0.011) were statistically significant in the Ti group, whereas only disc height restoration was significant in the PEEK group (P= 0.003). In patients undergoing stand-alone lateral lumbar interbody fusion to treat adjacent segment degeneration, Ti cages had a significantly lower overall subsidence rate compared with PEEK cages. Furthermore, Ti cages resulted in fewer recommendations for revision surgery. Whether greater pain reduction in the Ti group is associated with earlier or higher fusion rates needs to be further elucidated.

Relationship Between Preoperative Opioid Use and Postoperative Pain in Patients Undergoing Minimally Invasive Stand-Alone Lateral Lumbar Interbody Fusion

Relationship Between Preoperative Opioid Use and Postoperative Pain in Patients Undergoing Minimally Invasive Stand-Alone Lateral Lumbar Interbody Fusion

Incidence of adjacent-segment surgery following stand-alone lateral lumbar interbody fusion.

Adjacent-segment disease (ASD) requiring operative intervention is a relatively common long-term consequence of lumbar fusion surgery. Although the incidence of ASD requiring reoperation is well described for traditional posterior lumbar approaches (2.5%-3.9% per year), it remains poorly characterized for stand-alone lateral lumbar interbody fusion (LLIF). In this study, the authors report their institutional experience with ASD requiring reoperation after LLIF over an extended follow-up period of 4 years. Medical records were reviewed for 276 consecutive patients who underwent stand-alone LLIF by a single surgeon for degenerative spinal disorders. Inclusion criteria (single-stage, stand-alone LLIF without posterior supplementation, with no prior lumbar instrumentation, and a minimum of 4 years of follow-up) were met by 182 patients, who were analyzed for operative ASD incidence (per-year rate), demographics, and Oswestry Disability Index (ODI) score. Operative ASD was strictly defined as new-onset pathology following index surgery at directly adjacent levels to the prior construct. Operative, rather than symptomatic or radiographic, ASD was analyzed to provide a consistent and impactful endpoint while avoiding retrospective diagnosis. The study cohort of 182 patients had an operative ASD rate of 3.3% (n = 6 procedures) over 4 years of follow-up, for an incidence on Kaplan-Meier survival analysis of 0.88% (95% CI 0.67%-1.09%) per year. In comparing patients with operative ASD with those without, there were no significant differences in mean age (53.7 vs 56.2 years), male sex (33.3% vs 44.9%), smoking status (16.7% vs 25.0%), or number of levels fused (mean 1.33 vs 1.46). The operative ASD cohort had a greater mean BMI (37.3 vs 30.2, p < 0.01). Operative ASD patients had lower baseline ODI scores (33.8 vs 48.3, p = 0.02); however, no difference was observed in ODI at 6 weeks (34.0 vs 39.0) or 3 months (16.0 vs 32.8) postoperatively. The incidence of ASD in LLIF for degenerative lumbar etiologies in this cohort was 0.88% (95% CI 0.67%-1.09%) per year. Meanwhile, the reported reoperation rates for ASD in posterior spinal approaches was 2.5% to 3.9% per year, which implies that LLIF may be preferable for well-selected patients.

P45. The predictive value of a novel site-specific MRI-based bone quality assessment, endplate bone quality (EBQ), for Severe Cage Subsidence among patients undergoing standalone lateral lumbar interbody fusion

<h3>BACKGROUND CONTEXT</h3> Methods to measure bone quality using opportunistic imaging have recently been developed, including quantitative computed tomography (QCT), which allows for site-specific volumetric bone mineral density (vBMD) measurement, such as pedicles or endplates. Studies have shown these site-specific QCT measurements had more predictive value for site-specific complications than standard L1/2 measurements. Recently, MRI-based assessments of the vertebral bone quality (VBQ), which measures trabecular bone quality, were also introduced. However, there have been few studies that investigate the association between site-specific MRI bone assessment and osteoporosis related complications in patients undergoing lumbar interbody fusion. In this work, we created a novel site-specific MRI-based assessment of the endplate bone quality (EBQ) and assessed its predictive value for severe cage subsidence following standalone lateral lumbar interbody (SA-LLIFF) fusion. <h3>PURPOSE</h3> The purpose is to introduce a novel MRI-based site-specific bone quality assessment, EBQ, and investigate the predictive value of EBQ for severe cage subsidence after SA-LLIF compared with standard VBQ. <h3>STUDY DESIGN/SETTING</h3> A retrospective observational study at a single academic institution. <h3>PATIENT SAMPLE</h3> Patients undergoing SA-LLIF between 2008-2019 with available preoperative CT and T1-weighted MRIs of the lumbar spine as well as postoperative lumbar radiographs or CTs. <h3>OUTCOME MEASURES</h3> Severe cage subsidence (Grade 2 or 3) within 5-14 month after SA-LLIF. <h3>METHODS</h3> We retrospectively reviewed the records of SA-LLIF patients. Cage subsidence was assessed using the classification of Marchi et al. and severe cage subsidence was defined as grade 2 or 3. We measured VBQ as shown in the original article by Ehresman et al. EBQ was measured using preoperative non-contrast T1-weighted MRIs of the lumbar spine. The regions of interest were the subchondral bones of upper and lower endplates at the operated level, and the average signal intensity of both endplates was divided by that of the cerebrospinal fluid space at the level of L3. As a confounding factor, vBMD was measured using asynchronous QCT. Bivariate and multivariable analysis with generalized linear mixed models were performed with setting binary severe subsidence as the outcome. Statistical significance was set at p=0.05. The quality of fit was assessed using Akaike's information criterion. <h3>RESULTS</h3> A total of 205 levels in 89 patients were included in the final analysis. There were 50 levels (24.4%) which demonstrated severe subsidence. QCT-vBMD was significantly lower in severe subsidence group (Mean (SD) 97.4 (34.4) vs 110.1(33.4), p=0.021). Both VBQ and EBQ were significantly higher in severe subsidence group (VBQ: Mean (SD) 2.67 (1.08) vs 2.39 (0.44), p=0.010; EBQ Mean (SD) 5.09 (2.20) vs 4.31 (1.09), p=0.001). In multivariate analyses adjusted with QCT-vBMD, EBQ showed significant association with severe cage subsidence (OR (95% confidential interval) = 1.94 (1.36-3.63), p=0.038), whereas VBQ only showed a marginal trend (p=0.071). The EBQ based prediction model for severe subsidence showed better goodness of fit compared to VBQ based model. (AIC EBQ 190 vs VBQ 192). <h3>CONCLUSIONS</h3> We introduced a novel MRI-based site-specific bone quality assessment. High EBQ was an independent factor for severe cage subsidence after SA-LLIF and the EBQ-based model showed better goodness of fit compared to VBQ-based model. Given the availability of preoperative MRIs, EBQ assessment prior to SA-LIFF may provide insight into a patient's risk for severe subsidence. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.

75. Evaluation of cage subsidence in standalone lateral lumbar interbody fusion: Novel 3D printed titanium versus polyetheretherketone (PEEK) cage

<h3>BACKGROUND CONTEXT</h3> Lateral lumbar interbody fusion (LLIF) is a common treatment for degenerative spine diseases. However, implant subsidence is a prevalent complication especially in stand-alone cases, which can negatively affect patient outcomes. The novel 3D-printed titanium (Ti) cages with porous architecture are reportedly more osteoconductive, maximize bone-to-implant contact, and have more compressive shear strength under physical force. Nevertheless, the subsidence rate of these new Ti cages compared to polyetheretherketone (PEEK) cages has not been investigated in standalone cases. <h3>PURPOSE</h3> This study aims to compare the early subsidence rate (6-12 months) of standalone Ti vs PEEK interbody cages after LLIF. <h3>STUDY DESIGN/SETTING</h3> Retrospective study. <h3>PATIENT SAMPLE</h3> A total of 113 patients and 186 levels. <h3>OUTCOME MEASURES</h3> Early cage subsidence. <h3>METHODS</h3> A retrospective study of 113 patients (186 levels) who underwent LLIF surgery with Ti or PEEK cages was conducted. Early subsidence was measured in each treated level using the Marchi et al. classification in radiographs or CT scans acquired at 6-12 months follow-up. Multivariate logistic regression analyses with generalized mixed models, setting subsidence as the outcome variable and including cage type (Ti vs PEEK) as well as significant and trending variables (p<0.10) in univariate analyses, was conducted. <h3>RESULTS</h3> In total, 51 female and 62 male patients were analyzed. The median (IQR) age at surgery was 60.0 (51.0-70.0) years. Of the 186 levels, 119 levels were treated using PEEK and 67 levels with Ti cages. The overall subsidence rate for Grades I-III was significantly less in the Ti vs the PEEK group (p=0.003). For high-grade subsidence (Grade II or III), Ti cages also demonstrated a subsidence rate (3.0%) that was significantly less compared to PEEK cages (18.5%)(p= 0.002). Multivariate analysis showed that patients treated with Ti cages were less likely to develop severe subsidence compared to those treated with PEEK (OR= 0.05, 95%CI= 0.01, 0.30)(p= 0.001). <h3>CONCLUSIONS</h3> Our study demonstrated that 3D-printed novel Ti cages had a significantly lower early subsidence rate compared to PEEK cages in standalone LLIF patients. <h3>FDA DEVICE/DRUG STATUS</h3> Titanium and PEEK Cage (Approved for this indication).

Poor Bone Quality, Multilevel Surgery, and Narrow and Tall Cages Are Associated with Intraoperative Endplate Injuries and Late-onset Cage Subsidence in Lateral Lumbar Interbody Fusion: A Systematic Review.

A major complication of lateral lumbar interbody fusion (LLIF) is cage subsidence, which may lead to clinical problems, including loss of disc height correction, altered spinal alignment, recurrent pain, and vertebral body fracture. A thorough review of the current knowledge about the risk factors for the two types of cage subsidence after LLIF-intraoperative endplate injury and late-onset cage subsidence-could bring attention to well-established risk factors for clinical consideration while identifying any incompletely characterized factors that require further research to clarify. We performed a systematic review to answer the following questions: (1) Are bone quality and surrogates for bone quality, such as patient age and sex, associated with an increased likelihood of cage subsidence? (2) Are implant-related factors associated with an increased likelihood of cage subsidence? Two independent reviewers comprehensively searched Medline, Embase, Cochrane Library, PubMed, and Web of Science from 1997 to 2020 to identify all potential risk factors for cage subsidence after LLIF. Discrepancies were settled through discussion during full-text screening. Search terms included "lateral" AND "interbody fusion" AND "subsidence" OR "settling" OR "endplate injury" OR "endplate violation" WITHOUT "cervical" OR "transforaminal" OR "biomechanical." Eligible studies were retrospective or prospective comparative studies, randomized controlled trials, and case series with sample sizes of 10 patients or more reporting risk factors for cage subsidence or endplate injury after LLIF. Studies that involved cervical interbody fusions and biomechanical and cadaveric experiments were excluded. The Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach was used to assess the studies' quality of evidence. The initial database review found 400 articles. Thirty-four articles with moderate- to very-low-quality evidence met the inclusion criteria for analysis. A total of 3233 patients (58% [1860] of whom were female) were included in this review. Two types of cage subsidence were reviewed: late-onset cage subsidence, which occurs gradually postoperatively, and intraoperative endplate injury, which is derived from iatrogenic endplate violation during endplate preparation or cage insertion. Among 20 studies with moderate quality of evidence according to the GRADE criteria, eight studies reported risk factors for cage subsidence related to bone mineral density and its surrogates and 12 studies focused on risk factors regarding implant factors, including cage dimension, cage material, construct length, and supplementary instrumentation. Patients with a dual x-ray absorptiometry T-score of -1.0 or less, age older than 65 years, and female sex were considered to have a high risk of both types of cage subsidence. Regarding cage size, cage width ≥ 22 mm helped to avoid late-onset cage subsidence, and cage height ≤ 11 mm was recommended by some studies to avoid intraoperative endplate injuries. Studies recommended that multilevel LLIF should be conducted with extra caution because of a high risk of losing the effect of indirect decompression. Studies found that standalone LLIF might be sufficient for patients without osteoporosis or obesity, and supplementary instrumentation should be considered to maintain the postoperative disc height and prevent subsidence progression in patients with multiple risk factors. The effect of the bone graft, cage material, endplate condition, and supplementary instrumentation on cage subsidence remained vague or controversial. Patients with poor bone density, patients who are older than 65 years, and female patients should be counseled about their high risk of developing cage subsidence. Surgeons should avoid narrow cages when performing LLIF to minimize the risk of late-onset cage subsidence, while being cautious of an aggressive attempt to restore disc height with a tall cage as it may lead to intraoperative endplate injury. For multilevel constructs, direct decompression approaches, such as posterior and transforaminal LIF, should be considered before LLIF, since the effect of indirect decompression may be difficult to maintain in multilevel LLIF because of high risks of cage subsidence. The effect of the cage material and supplementary instrumentation require stronger evidence from prospectively designed studies with larger sample size that randomly assign patients to polyetheretherketone (PEEK) or titanium cages and different fixation types. Future research on intraoperative endplate injuries should focus on the specific timing of when endplate violation occurs with the help of intraoperative imaging so that attempts can be made to minimize its occurrence. Level IV, therapeutic study.

Evaluation of cage subsidence in standalone lateral lumbar interbody fusion: novel 3D-printed titanium versus polyetheretherketone (PEEK) cage.

This study aims to compare the early subsidence rate (6-12months) of standalone novel 3D-printed titanium (Ti) versus polyetheretherketone (PEEK) interbody cages after lateral lumbar interbody fusion (LLIF). A retrospective study of 113 patients (186 levels) who underwent LLIF surgery with Ti or PEEK cages was conducted. Early subsidence was measured in each treated level using the Marchi et al. classification in radiographs or CT scans acquired at 6-12months follow-up. Multivariate logistic regression analyses with generalized mixed models, setting subsidence as the outcome variable and including cage type (Ti vs PEEK) as well as significant and trending variables (p < 0.10) in univariate analyses, were conducted. In total, 51 female and 62 male patients were analyzed. The median [IQR] age at surgery was 60.0 [51.0-70.0] years. Of the 186 levels, 119 levels were treated using PEEK and 67 levels with Ti cages. The overall subsidence rate for Grades I-III was significantly less in the Ti versus the PEEK group (p = 0.003). For high-grade subsidence (Grade II or III), Ti cages also demonstrated a subsidence rate (3.0%) that was significantly less compared to PEEK cages (18.5%) (p = 0.002). Multivariate analysis showed that patients treated with Ti cages were less likely to develop severe subsidence compared to those treated with PEEK (OR = 0.05, 95% CI = 0.01, 0.30) (p = 0.001). Our study demonstrated that 3D-printed novel Ti cages had a significantly lower early subsidence rate compared to PEEK cages in standalone LLIF patients.

The Feasibility of 3D Intraoperative Navigation in Lateral Lumbar Interbody Fusion: Perioperative Outcomes, Accuracy of Cage Placement and Radiation Exposure.

Retrospective cohort study. To evaluate perioperative outcomes, accuracy of cage placement and radiation exposure in lateral lumbar interbody fusion (LLIF) using 3D intraoperative navigation (ION), compared to conventional 2D fluoroscopy only. The perioperative outcomes and accuracy of cage placement were examined in all patients who underwent LLIF using ION (ION group) or fluoroscopy only (non-ION group) by a single surgeon. The radiation exposure was examined in patients who underwent stand-alone LLIF. A total of 87 patients with 154 levels (ION 49 patients with 79 levels/ non-ION 38 patients with 75 levels) were included. There were no significant differences in operative time (ION 143.5 min vs. non-ION 126.0 min, P = .406), time from induction end to surgery start (ION 31.0 min vs. non-ION 31.0 min, P = .761), estimated blood loss (ION 37.5 ml vs. non-ION 50.0 ml, P = .351), perioperative complications (ION 16.3% vs. non-ION 7.9%, P = .335) and length of stay (ION 50.6 hours vs. non-ION 41.7 hours, P = .841). No significant difference was found in the accuracy of cage placement (P = .279). ION did not significantly increase total radiation dose (ION 51.0 mGy vs. non-ION 47.4 mGy, P = .237) and tended to reduce radiation dose during the procedure (ION 32.2 mGy vs. non-ION 47.4 mGy, P = .932). The perioperative outcomes, accuracy of cage placement and radiation exposure in LLIF using ION were comparable to those using fluoroscopy only. The use of ION in LLIF was feasible, safe and accurate and may reduce radiation dose to the surgeon and surgical team.

Cadaveric biomechanical analysis of multilevel lateral lumbar interbody fusion with and without supplemental instrumentation

BackgroundThis study was to evaluate and compare the biomechanical features of multilevel lateral lumbar interbody fusion (LLIF) with or without supplemental instrumentations.MethodsSix human lumbar specimens were tested under multidirectional nondestructive moments (7.5 N·m), with a 6 degree-of-freedom spine simulator. The overall and intervertebral range of motion (ROM) were measured optoelectronically. Each specimen was tested under the following conditions at L2–5 levels: intact; stand-alone; cage supplemented with lateral plate (LP); cage supplemented with unilateral or bilateral pedicle screw/rod (UPS or BPS).ResultsCompared with intact condition, the overall and intersegmental ROM were significantly reduced after multilevel stand-alone LLIF. The ROM was further reduced after using LP instrumentation. In flexion-extension (FE) and axial rotation (AR), pedicle screw/rod demonstrated greater overall ROM reduction compared to LP (P < 0.01), and bilateral greater than unilateral (P < 0.01). In lateral bending (LB), BPS demonstrated greater overall ROM reduction compared to UPS and LP (P < 0.01), however, UPS and LP showed similar reduction (P = 0.245). Intervertebral ROM reductions showed similar trend as the overall ones after using different types of instrumentation. However, at L2/3 (P = 0.57) and L3/4 (P = 0.097) levels, the intervertebral ROM reductions in AR were similar between UPS and LP.ConclusionsThe overall and intervertebral stability increased significantly after multilevel LLIF with or without supplemental instrumentation. BPS provided the greatest stability, followed by UPS and LP. However, in clinical practice, less invasive adjunctive fixation methods including UPS and LP may provide sufficient biomechanical stability for multilevel LLIF.