Severe Subsidence Research Articles

Surface Subsidence Characteristics and Causes Analysis in Ningbo Plain by Sentinel-1A TS-InSAR

In recent years, the Ningbo Plain has experienced significant surface subsidence due to urbanization and industrialization, combined with the area’s unique geological and hydrological conditions. To study the surface subsidence and its causes in the Ningbo Plain, this study analyzed 166 scenes of Sentinel-1A SAR images between January 2018 and June 2023. The time series interferometric synthetic aperture radar (TS-InSAR) technique was used to acquire surface subsidence information in the area. The causes of subsidence were analyzed. The results show that: (1) the annual deformation rate of the Ningbo Plain ranges from −44 mm/yr to 12 mm/yr between 2018 and 2023. A total of 15 major subsidence zones were identified by using both the subsidence rate map and optical imagery. The most severe subsidence occurred in the northern industrial park of Cixi City, with a maximum subsidence rate of −37 mm/yr. The study reveals that the subsidence issue in the main urban area has been significantly improved compared to the 2017 subsidence data from the Ningbo Bureau of Natural Resources and Planning. However, three new subsidence areas have emerged in the main urban area, located, respectively, in Gaoqiao Town, Lishe Town, and Qiuyi Village, with maximum rates of −29 mm/year, −24 mm/year, and −23 mm/year, respectively. (2) The causes of subsidence were analyzed using various data, including land use data, geological data, groundwater-monitoring data, and transportation network data. It is found that a strong link exists between changes in groundwater levels, compressible layer thickness, and surface subsidence. The groundwater levels changes and the soft soil layer thickness are the main natural factors causing subsidence in the Ningbo Plain. Additionally, the interaction between static loads from large-scale industrial production and urban construction, along with the dynamic loads from transportation networks, contribute significantly to surface subsidence in the Ningbo Plain. The results from this study enhance the understanding of the driving factors of subsidence in the Ningbo Plain, which can provide necessary guidance for the economic development and decision-making in the region, helping to manage and potentially mitigate future subsidence issues.

Transforaminal lumbar interbody fusion subsidence: computed tomography analysis of incidence, associated risk factors, and impact on outcomes.

The aims of this study were to 1) define the incidence of transforaminal lumbar interbody fusion (TLIF) interbody subsidence; 2) determine the relative importance of preoperative and intraoperative patient- and instrumentation-specific risk factors predictive of postoperative subsidence using CT-based assessment; and 3) determine the impact of TLIF subsidence on postoperative complications and fusion rates. All adult patients who underwent one- or two-level TLIF for lumbar degenerative conditions at a multi-institutional academic center between 2017 and 2019 were retrospectively identified. Patients with traumatic injury, infection, malignancy, previous fusion at the index level, combined anterior-posterior procedures, surgery with greater than two TLIF levels, or incomplete follow-up were excluded. Interbody subsidence at the superior and inferior endplates of each TLIF level was directly measured on the endplate-facing surface of both coronal and sagittal CT scans obtained greater than 6 months postoperatively. Patients were grouped based on the maximum subsidence at each operative level classified as mild, moderate, or severe based on previously documented < 2-mm, 2- to 4-mm, and ≥ 4-mm thresholds, respectively. Univariate and regression analyses compared patient demographics, medical comorbidities, preoperative bone quality, surgical factors including interbody cage parameters, and fusion and complication rates across subsidence groups. A total of 67 patients with 85 unique fusion levels met the inclusion and exclusion criteria. Overall, 28% of levels exhibited moderate subsidence and 35% showed severe subsidence after TLIF with no significant difference in the superior and inferior endplate subsidence. Moderate (≥ 2-mm) and severe (≥ 4-mm) subsidence were significantly associated with decreases in cage surface area and Taillard index as well as interbody cages with polyetheretherketone (PEEK) material and sawtooth surface geometry. Severe subsidence was also significantly associated with taller preoperative disc spaces, decreased vertebral Hounsfield units (HU), the absence of bone morphogenetic protein (BMP) use, and smooth cage surfaces. Regression analysis revealed decreases in Taillard index, cage surface area, and HU, and the absence of BMP use predicted subsidence. Severe subsidence was found to be a predictor of pseudarthrosis but was not significantly associated with revision surgery. Patient-level risk factors for TLIF subsidence included decreased HU and increased preoperative disc height. Intraoperative risk factors for TLIF subsidence were decreased cage surface area, PEEK cage material, bullet cages, posterior cage positioning, smooth cage surfaces, and sawtooth surface designs. Severe subsidence predicted TLIF pseudarthrosis; however, the causality of this relationship remains unclear.

MRI Vertebral Bone Quality Correlates With Interbody Cage Subsidence After Anterior Cervical Discectomy and Fusion.

Retrospective observational study of consecutive patients. The purpose of the study was to evaluate VBQ as a predictor of interbody subsidence and to determine threshold values that portend increased risk of subsidence. Many risk factors have been reported for the subsidence of interbody cages in anterior cervical discectomy and fusion (ACDF). MRI Vertebral Bone Quality (VQB) is a relatively new radiographic parameter that can be easily obtained from preoperative MRI and has been shown to correlate with measurements of bone density such as DXA and CT Hounsfield Units. All patients who underwent 1- to 3-level ACDF using titanium interbodies with anterior plating between the years 2018 and 2020 at our tertiary referral center were included. Subsidence measurements were performed by 2 independent reviewers on CT scans obtained 6 months postoperatively. VBQ was measured on pre-operative sagittal T1 MRI by 2 independent reviewers, and values were averaged. Eight-five fusion levels in 44 patients were included in the study. There were 32 levels (38%) with moderate subsidence and 12 levels with severe subsidence (14%). The average VBQ score in those patients with severe subsidence was significantly higher than those without subsidence (3.80 vs. 2.40, P<0.01). A threshold value of 3.2 was determined to be optimal for predicting subsidence (AUC=0.99) and had a sensitivity of 100% and a specificity of 94.1% in predicting subsidence. VBQ strongly correlates with the subsidence of interbody grafts after ACDF. A threshold VBQ score value of 3.2 has excellent sensitivity and specificity for predicting subsidence. Spine surgeons can use VBQ as a readily available screening tool to identify patients at higher risk for subsidence. Level-IV.

Research and application of sinking-aided methods for circular open caisson under complex formation conditions: case study

Open caissons have been widely used owing to their good structural integrity and waterproofing performance, convenient construction, and low cost. However, sinking construction is affected by many factors, such as geological conditions, groundwater, designed depth, and self-weight. Improper measures may lead to severe subsidence of the surface and adjacent structures of an open caisson and even adversely affect its structure. This study using a large-diameter circular open caisson in the Jinshan Lake, Zhenjiang, first examines the causes of its substantial sinking and stagnation during construction. Owing to the different leading causes, sinking-aided methods differ. Therefore, these methods and their subsequent optimization schemes are established, and their effects are analyzed to provide a reliable reference for future related projects.

1066 Comparative Outcome Using Expandable Versus Static Cage in Direct Lateral Interbody Fusion for Degenerative Lumbar Disc Disease

INTRODUCTION: Subsidence has been a common concern or complication in patients undergoing TLIF with an expandable cage or standalone DLIF with a static cage. It could lead to further complications such as pseudoarthrosis, lumbar kyphosis, and radiculopathy. Recently, expandable technology has emerged in lateral interbody fusion, which could be delivered through the smaller surgical corridors. Therefore we sought to determine the extent of radiological outcome and subsidence rate in patients with expandable cages. METHODS: A retrospective review of patients who underwent DLIF was performed. Only patients with degenerative lumbar disc disease were included. Baseline demographic and radiographic outcomes such as cage subsidence, anterior and posterior disc height, foraminal dimensions, and other spinopelvic parameters were collected. The primary endpoint was severe cage subsidence (grade 2 and 3) per level according to the classification by Marchi et al. Multivariate Analysis was performed. RESULTS: 59 patients underwent DLIF with expandable (n = 25) and static (n = 34) cages respectively. Both expandable and static groups have comparable baseline demographic such as age, gender, BMI, and medical comorbidities. The average follow-up period was 16 months. Both groups also had a comparable rate of the standalone construct (40% vs 68%, p 0.088). Significant higher cage width and length were used in the expandable group. However, there were no statistically significant differences in the restoration of both anterior and posterior disc heights, foraminal height, and central canal diameter. A significantly lower rate of severe subsidence was observed in the expandable group (4% vs 26.5%, p = 0.023) compared to the static group. CONCLUSIONS: In our study, expandable cages in DLIF patients were observed to have a significantly lower rate of subsidence when compared to those who received static cages.

InSAR time series analysis of natural and anthropogenic coastal plain subsidence: A case of Hangjiahu plain

The early excessive groundwater exploitation caused extensive land subsidence in the Hangjiahu Plain (HJHP), threatening geological stability and infrastructure. Government restrictions on groundwater exploitation led to considerable changes in surface subsidence. To explore the distribution and causes of surface deformation after restrictions on groundwater exploitation, we used 46 Sentinel-1A TOPS images to detect the spatiotemporal distribution of surface deformation in the HJHP area from January 2019 to October 2022 by SBAS-InSAR technique and verified it with leveling results. Results indicated the following: (1) The uneven surface subsidence in the HJHP was relatively apparent, with the localized subsidence concentrated in a few areas. During InSAR monitoring, the maximum subsidence velocity reached −21.0 mm/yr. The most severe subsidence area was in the Shengze town industrial park, with remarkable subsidence bowls and a maximum subsidence of −85.8 mm. (2) Results were verified by comparing the InSAR results with leveling, and the results were in good agreement, indicating the reliability of the InSAR results. (3) Comprehensive analysis of the spatial distribution characteristics of surface subsidence, geological data and rainfall changes revealed that fault activity and rainfall changes had varying degrees of effect on surface subsidence in the HJHP area. (4) The comparison with land use data indicated that the built area was the dominant mechanism of surface subsidence in the study area. In addition, the effect of industrial activities on the surface cannot be ignored. The study results provide scientific data support for emergency disaster prevention work in the HJHP.

Mechanism the land subsidence from multiple spatial scales and hydrogeological conditions – A case study in Beijing-Tianjin-Hebei, China.

Study regionBeijing-Tianjin-Hebei (BTH) region, China Study focusBTH has long been suffering from severe and uneven land subsidence. Finding out the spatial evolution of land subsidence is helpful to collaborative prevention and control. We innovatively revealed the spatial distribution of land subsidence from the mountains to the coastal area along four hydrogeological profiles, and inferred the land subsidence mechanism on the overall scale, local plain scale and typical regional scale. Small Baseline Subsets Interferometric Synthetic Aperture Radar was employed to collect displacement information in the BTH region from January 2012 to January 2020. We obtained groundwater storage data from the Gravity Recovery and Climate Experiment. New hydrological insights for the regionOn the overall scale, from 2012 to 2019, the Changping-TongZhou district of Beijing suffered the most serious land subsidence, with an annual subsidence rate of 159 mm and a cumulative subsidence as high as 928 mm. On the local plain scale, areas experiencing severe subsidence were generally located in the central plain. Fractures in the area obviously influenced the spatial distribution of subsidence. On the typical regional scale, a positive correlation was found between land subsidence and groundwater depletion. The relationship between precipitation and land subsidence in Hebei was the most convincing (R2 = 0.64). This study provides a scientific basis for regional coordination in land subsidence control. Data availabilityData can be provided by the corresponding authors upon request.

An Investigation of Volcanic Ground Deformation Using InSAR Observations at Tendürek Volcano (Turkey)

Although approximately one-tenth of the world’s population lives near volcanoes, most of the 1500 active volcanoes are not monitored by ground-based instruments because of the cost and difficulty of access. Since the development of interferometric synthetic aperture radar (InSAR) in the 1990s, recent advances have allowed the near-real-time detection of surface deformations, one of the earliest markers of volcanic activity. According to the Global Volcanism Program, Turkey’s most recent eruption (involving gas and ash) occurred in the Tendürek volcano in 1885. An explosion in the Tendürek volcano, which continues to actively output gas and steam, would be a critical issue for the life and property of the people living nearby. In this context, we processed the Sentinel-1 data collected by the European Space Agency using the Stanford Method for Persistent Scatterers, and the surface deformations of the Tendürek volcano were investigated. In addition, we applied two different atmospheric correction approaches (linear phase-based tropospheric correction and the Generic Atmospheric Correction Online Service for InSAR) to reduce atmospheric effects and found that the linear phase-based tropospheric correction model produced lower standard deviation values. Subsequently, the mean deformation velocity maps, displacement time series, and deformation components in the line-of-sight direction were calculated. The results showed that the most severe subsidence was −11 mm/yr on the upper slopes of the Tendürek volcano. Although the lower slopes of the subsidence region have a lower settlement rate, the subsidence has a peak-caldera-centered location.

Land Subsidence in the Singapore Coastal Area with Long Time Series of TerraSAR-X SAR Data

Global sea level rise is a major environmental concern for many countries and cities, particularly for low-lying coastal areas where urban development is threatened by the combined effects of sea level rise and land subsidence. This study employed an improved two-layer network Persistent Scatterers Interferometric Synthetic Aperture Radar (PS-InSAR) technology to obtain high-precision land subsidence in Singapore from 2015 to 2019. Landsat images from 1973 to 2020 were also utilized to extract changes in Singapore’s coastline. Geological, topographical, and global sea level rise data were integrated to investigate the causes and impacts of land subsidence in Singapore. The results indicate that the areas with severe subsidence coincide with land reclamation areas, where subsidence is mainly due to soil consolidation. Based on WorldDEM, land subsidence, and sea level rise data, the maximum inundation depth in Singapore by 2050 is estimated to be 1.24 m, with the Marina Bay area in Singapore’s central business district being the most vulnerable to sea level rise. This study provides data support and a scientific basis for understanding the impact of land subsidence on Singapore’s coastal areas under the influence of multiple factors using advanced InSAR technology.

Modeling of land subsidence using GIS-based artificial neural network in Yunlin County, Taiwan

In this study, the land subsidence in Yunlin County, Taiwan, was modeled using an artificial neural network (ANN). Maps of the fine-grained soil percentage, average maximum drainage path length, agricultural land use percentage, electricity consumption of wells, and accumulated land subsidence depth were produced through geographic information system spatial analysis for 5607 cells in the study area. An ANN model based on a backpropagation neural network was developed to predict the accumulated land subsidence depth. A comparison of the model predictions with ground-truth leveling survey data indicated that the developed model had high accuracy. Moreover, the developed model was used to investigate the relationship of electricity consumption reduction with reductions in the total area of land with severe subsidence (> 4 cm per year); the relationship was approximately linear. In particular, the optimal results were obtained when decreasing the electricity consumption from 80 to 70% of the current value, with the area of severe land subsidence decreasing by 13.66%.

Study on surrounding rock failure mechanism and rational coal pillar width of the gob‐side coal roadway under influence of intense dynamic pressure

AbstractA reasonable width of the coal pillar is very important to the surrounding rock control of the gob‐side roadway. An unreasonable width of the coal pillar will make the roadway to be located within the range of strong mining influence, leading to severe deformation of the roadway. Severe subsidence at the coal pillar side of the roof and serious coal pillar deformation are problems caused by strong dynamic pressure due to mining in the gob‐side coal roadway. This paper studies the surrounding rock instability mechanism and rational coal pillar width of the gob‐side coal roadway under the influence of intense dynamic pressure. The results show that: (1) Under the condition of large mining height, the roadway overburden is a hinged structure, and an unreasonable coal pillar width makes the gob‐side coal roadway to be located below the main roof fracture line. The rotary movement of the key block of the main roof is the main reason for the roadway deformation. (2) According to the evolution law of stress field, displacement field and plastic zone of surrounding rock of roadway under different coal pillar widths during roadway driving and mining were studied, and it is concluded that a 6‐m‐width coal pillar is the most reasonable. (3) Based on the stress distribution and plasticizing range of surrounding rock in a narrow pillar roadway, the combined support scheme of “anchor cable + grouting + single prop” is proposed and applied to engineering practice. The practice results show that the roadway deformation is well controlled, and the safe mining of the working face is realized.

Comparison of radiological and clinical outcomes of 3D-printed artificial vertebral body with Titanium mesh cage in single-level anterior cervical corpectomy and fusion: A meta-analysis.

This meta-analysis aimed to determine whether 3D-printed artificial vertebral body have superior clinical and radiographic outcome than Titanium Mesh Cage(TMC) in single-level anterior cervical corpectomy and fusion. A comprehensive search of the PubMed, Embase, Cochrane Library, Web of Science, and CNKI (China National Knowledge Infrastructure) databases was conducted to find randomized control trials (RCTs) or cohort studies that compared 3D-printed artificial vertebral body with conventional Titanium Mesh Cage (TMC) in single-level anterior cervical corpectomy and fusion (SL-ACCF). Operation time; intraoperative blood loss; subsidence of vertebral body; preoperative, and final follow-up C2-C7 Cobb angle, Japanese Orthopedic Association (JOA) scores, and Visual Analog Scale(VAS) scores were collected from eligible studies for meta-analysis. We included 6 cohort studies with 341 patients. The results of the meta-analysis showed that the 3D group has a shorter operation time than the traditional TMC group(p = 0.04) and the TMC group had more severe subsidence(≥3 mm) of vertebral body than the 3D group(p < 0.0001). And the cervical C2-C7 Cobb angle in the 3D group was larger than that in the TMC group at the final follow-up. This meta-analysis demonstrates that 3D-printed artificial vertebral body is superior to traditional TMC in reducing the operation time and maintaining the postoperative vertebral height and restoring sagittal balance to the cervical spine in single-level anterior cervical corpectomy and fusion.

Groundwater over-exploitation driven ground subsidence in the himalayan piedmont zone: Implication for aquifer health due to urbanization

Unsustainable groundwater exploitation often triggers inelastic aquifer compaction, endangering future groundwater potential. The Himalayan piedmont fan regions are undergoing fast urbanization and experiencing rapid groundwater depletion and water table drop. The piedmont fans have laterally varying aquifer geometry with slope-dominated aquifer water flow and experience variable spatiotemporal changes in response to groundwater depletion. We estimated the ground deformation over piedmont fans around Chandigarh (India), a growing urban centre, during 2014–2022 using satellite-based Interferometric Point Target Analysis (IPTA). We used both ascending and descending Differential Interferometric Synthetic Aperture Radar (DInSAR) acquisition modes to derive the vertical ground deformation by combining their line of sight (LOS) velocities. The region is experiencing vertical subsidence up to ∼60 mm/yr with prominent hotspots, where the temporal subsidence is compared with the groundwater cone of depression and urbanization over decades. Comparing the subsidence with the aquifer parameters from the bore wells suggests that the clay confining aquifer level III and semiconfined level II in the distal fan are experiencing the highest subsidence. The stress-strain relationship of these hotspot regions reveals the inelastic compaction of the aquifers producing severe subsidence. The piedmont zones of the Himalayas with identical aquifer geometry and population growth are facing similar challenges, and the combined DInSAR-IPTA and observational groundwater data modeling could provide a robust assessment for effective groundwater-aquifer health monitoring and management.

Combination of historical and modern data to decipher the geomorphic evolution of the Innere Ölgruben rock glacier, Kaunertal, Austria, over almost a century (1922–2021)

AbstractRock glaciers are cryo‐conditioned downslope‐creeping landforms in high mountains. Their dynamics are changing due to external factors influenced by climate change. Although there has been a growing scientific interest in mountain permafrost and thus in rock glaciers in recent years, their historical development, especially before the first alpine‐wide aerial image flights in the 1950s, has hardly been researched. Therefore, we utilize a historical stereophotogrammetric map from 1922 and historical flow velocity profiles (1938–1953) and relate them to data derived from historical aerial photographs and airborne laser scanning data in several time slices between 1953 and 2021. By doing so, the development of flow velocity, surface elevation changes, and frontal advance of the two lobes of the composite rock glacier Inner Ölgrube, Kaunertal, Austria, is analyzed and compared over almost a century. Results indicate an increased frontal advance in the laterally confined area of one lobe and a severe subsidence in the upper area of both lobes between 1922 and 1953. Whereas the former could be explained by a combination of the short warm phase in the 1940s and 1950s and the (subsurface) topography, the latter might be attributed to the strong melting of superimposed debris‐covered dead ice bodies, a relict of the Little Ice Age (LIA) glaciation. Both factors might also contribute to the increased flow velocities between 1938 and 1953, which are still recognizable in the 1953–1970 time step. Although both lobes follow a general similar trend, which is in line with the alpine‐wide trend of flow velocity acceleration in the 1990s, differences in the geomorphic development of the two lobes were identified. In addition to a slightly varying evolution of the flow velocities, the timing and magnitude of the volume changes are different. Furthermore, both lobes display a dissimilar mechanism of frontal advance over the entire study period. Because the external forcing is identical, the varying development might be attributed to variations in internal structure, bedrock topography, or upslope connection of the lobes. Due to the lateral constriction, the subsurface topography, and the LIA maximum extent of the glacier, it is assumed that the geomorphic development of the Innere Ölgruben rock glacier, particularly before 1953, represents a special case, and the results are not simply transferable to other rock glaciers.

Risk Factors for Allograft Subsidence Following Anterior Cervical Discectomy and Fusion

The purpose this study was to precisely characterize patterns of allograft subsidence following anterior cervical discectomy and fusion (ACDF) utilizing computed tomography scans, determine risk factors for cervical allograft subsidence, and investigate the impact of subsidence on pseudarthrosis rates. We performed a retrospective review of patients undergoing 1-to 3-level ACDF utilizing allograft interbodies with anterior plating between 2011 and 2019. Subsidence measurements were performed by 2 independent reviewers on computed tomography scans obtained 6months postoperatively. Subsidence was then classified as mild if subsidence into the inferior and superior endplates were both ≤2mm, moderate if the worst subsidence into the inferior- or superior endplate was between 2 and 4mm, or severe if the worst subsidence into the inferior- or superior endplate was ≥4mm. Multivariate analysis was performed to identify risk factors for the development of subsidence. We identified 98 patients (152 levels) for inclusion. A total of 73 levels demonstrated mild subsidence (≤2mm), 61 demonstrated moderate subsidence (2-4mm), and 18 demonstrated severe subsidence (≥4mm). On multivariate analysis, risk factors for severe subsidence included excessive vertebral endplate resection and lower screw tip to vertebral body height ratio. Severe subsidence was associated with an increased rate of pseudarthrosis (94.1% vs. 13.6%) without an associated increase in reoperation rate. Following ACDF with allograft interbodies, 50% of interbodies will subside >2mm and 10% of interbodies will subside >4mm. Risk factors for severe subsidence should be mitigated to decrease the risk of pseudarthrosis.

Characterizing Spatiotemporal Patterns of Land Subsidence after the South-to-North Water Diversion Project Based on Sentinel-1 InSAR Observations in the Eastern Beijing Plain

The eastern Beijing plain has been suffering severe subsidence for the last decades, mainly associated with the long-term excessive extraction of groundwater resource. Since the end of 2014, the annual water supply in Beijing plain has reached several hundred million cubic meters because of the South-to-North Water Diversion (SNWD) Project, which has reduced the groundwater exploitation and changed the status of land subsidence. In this work, we first obtain the current spatiotemporal variations of land subsidence in the eastern Beijing plain by using progressive small baseline subsets (SBAS) InSAR time series analysis method with Sentinel-1 SAR data acquired from July 2015 to December 2021. Then, we analyze the correlations between InSAR-derived subsidence and groundwater level change by applying the cross wavelet method. The results show that two major subsidence zones are successfully detected with the maximum deformation rate of −150 mm/yr and maximum cumulative deformation of −950 mm. Besides, the ground deformation at different stages from 2016 to 2021 reveal that the area and magnitude of major deformation significantly slow down, even in the regions with severe subsidence, especially in the year of 2017, which is about two years later than the start time of SNWD Project in Beijing. Further, we find the InSAR-derived subsidence lags groundwater level change with about 1–2-month lagging time, indicating that the dynamic variation of groundwater level fluctuation may be the main factor affecting the uneven subsidence in the severe subsiding zones. Last, differential subsidence rates are identified at both sides of geological faults, such as Nankou-Sunhe fault and Nanyuan-Tongxian fault, from the observed deformation map, which could be explained that the groundwater flow is blocked when a fault is encountered. These findings can provide significant information to reveal the deformation mechanisms of land subsidence, establish the hydrogeological models and assist decision-making, early warning and hazard relief in Beijing, China.

P45. Titanium cervical cage subsidence: postoperative CT analysis defining incidence and associated risk factors

<h3>BACKGROUND CONTEXT</h3> Substantial variability in both the measurement and classification of subsidence limits the strength of conclusions that can be drawn from previous studies. <h3>PURPOSE</h3> The purpose of this study was to precisely characterize patterns of cervical cage subsidence utilizing computed tomography scans, determine risk factors for cervical cage subsidence and investigate the impact of subsidence on pseudarthrosis rates. <h3>STUDY DESIGN/SETTING</h3> Retrospective cohort study. <h3>METHODS</h3> We performed a retrospective review of a patients who underwent one- to three-levels of ACDF utilizing titanium interbodies with anterior plating between the years 2018 to 2020. Subsidence measurements were performed by two independent reviewers on CT scans obtained 6 months postoperatively. Subsidence was then classified as mild if subsidence into the inferior and superior endplate were both ≤2mm, moderate if the worst subsidence into the inferior or superior endplate was between 2 to 4mm, or severe if the worst subsidence into the inferior or superior endplate was ≥4mm. <h3>RESULTS</h3> A total of 51 patients (100 levels) were included in this study. A total of 48 levels demonstrated mild subsidence (<2mm), 38 demonstrated moderate subsidence (2–4mm), and 14 demonstrated severe subsidence (>4mm). Risk factors for severe subsidence included male gender, multilevel constructs, greater mean vertebral height loss, increased cage height, lower Taillard Index, and lower screw tip to vertebral body height ratio. Severe subsidence was not associated with an increased rate of pseudarthrosis. <h3>CONCLUSIONS</h3> Following ACDF with titanium cervical cages, subsidence is an anticipated postoperative occurrence and is not associated with an increased risk of pseudarthrosis. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.

A skin-core debonding quantitative algorithm based on hexagonal units reconstruction for air-coupled ultrasonic C-scan images of honeycomb sandwich structure

Honeycomb Sandwich Structure (HSS) is widely used in the aerospace industry. The skin-core debonding in HSS can grow to reach a critical size, leading to the sudden failure of structures. Due to the blurry edges on the C-scan image caused by honeycomb units with periodic honeycomb walls, accurate quantification of debonding is still a challenge. In this paper, accurate debonding quantification of HSS based on air-coupled ultrasonic C-scan and hexagonal units reconstruction is proposed. The debonding boundary identification is accurate to the interior of the honeycomb units by partial debonding units division based on calculating the total amplitude of all scanning points within the unit. The detailed process was presented with key steps as ultrasonic air-coupled C-scan for HSS, hexagonal units reconstruction based on peak points on C-scan images, units classification by K-means clustering algorithm, and units division according to the total amplitude. Four types of debonding, including film sticking, adhesive removal, slight subsidence, and severe subsidence, are used to evaluate the effectiveness of the method. The results show that the proposed method can describe and quantify-four kinds of debonding defects reliably and it is ideally suited for air-coupled ultrasonic C-scan image processing of periodic structures.

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.

LAND SUBSIDENCE MONITORING AND ANALYSIS IN FUZHOU BASED ON INSAR AND MULTISPECTRAL REMOTE SENSING TECHNOLOGY

Abstract. Interferometric Synthetic Aperture Radar (InSAR) technology has millimeter level measurement accuracy and has great advantages in urban land subsidence monitoring. Meanwhile, multispectral remote sensing technique can also provide a large amount of urban features changes information for analyzing the causes of land subsidence. In this study, SAR and multispectral images are both used to monitor and analyze land subsidence in Fuzhou of China. 115 scenes Sentinel-1 SAR images from May 2017 to May 2021 are used based on the Persistent Scatterers Interferometric (PSI) method to evaluate the land subsidence in Fuzhou, while Sentinel-2 multispectral images are used to evaluate several remote sensing indexes. During SAR data processing, Generic Atmospheric Correction Online Service for InSAR (GACOS) data is used to remove atmospheric errors for higher accuracy land subsidence. In order to analyze the relationship between the land subsidence and land cover changes in urban areas, the Soil-Adjusted Vegetation Index (SAVI), Normalized Difference Built-up Index (NDBI) and Modified Normalized Difference Water Index (MNDWI) of the main subsidence areas are obtained based on Sentinel-2 multispectral images from 2016 to 2021. In the end, it is found that the land subsidence in some areas exceeded 12 mm/year in Fuzhou. The time series of four areas with severe subsidence were analyzed, and the cumulative subsidence reached about 60 mm. Besides, the spatial distribution and temporal changes of vegetation, buildings and water bodies in these areas were obtained based on the multispectral data, it is found there is very less relationship between the land subsidence and the urban features. It is concluded that that the main causes of the land subsidence are the changes of land internal components such as groundwater and others.