Risk Of Subsidence Research Articles

Modular Fluted Titanium Stems in Revision Hip Arthroplasty.

➤ Modular fluted titanium stems have become the implant of choice for most femoral component revisions as they have a lower risk of subsidence, thigh pain, femoral fracture, and stress shielding compared with previously used extensively coated cobalt-chromium stems.➤ Modularity of the femoral component allows for optimal and independent fit and fill of the proximal and distal femoral segments, permitting immediate axial and rotational stability in shorter diaphyseal segments (<4 cm of scratch fit), thus reducing the risk of subsidence. Modularity also allows for independent adjustment of version of the proximal body relative to the distal stem, thus improving joint stability. The ability to make small adjustments in vertical and lateral offset further reduces the potential for instability and leg-length discrepancy, and the use of a titanium implant minimizes the risk of stress shielding compared with cobalt-chromium stems.➤ In several retrospective case series, excellent mid-term to long-term outcomes and low complication rates have been observed with the use of modular fluted titanium stems in femoral revisions.➤ The major disadvantages to the routine use of modular fluted titanium stems are the potential for taper junction failure (corrosion or fracture) and the increased cost of these stems compared with nonmodular stems.

Vertebral body resection and lumbar corpectomies

Corpectomies in the lumbar spine are unique operations with important and well-deserving nuances that determine their ultimate safety and efficacy. Lumbar vertebral resections are indicated in deformity and non-deformity settings. For deformities, they are reserved for those that are severe and rigid. Infections, fractures, and tumors that compromise the weight-bearing capacity of the anterior and middle columns of the spine are also indicated for lumbar vertebrectomy. Anterior column structural support is required in non-deformity situations and may be accomplished with the use of polymethyl methacrylate (PMMA) cement, osseous strut grafts (i.e. allografts/autograft), or titanium cages (static vs. expandable). The newest generation of cages have wide, rectangular footprints that span the apophyseal ring and provide a sound biomechanical environment and minimize the risk of cage subsidence compared to those with circular footprints. Neural decompression and placement of structural support can be accomplished by a variety of surgical approaches. While a traditional anterior approach is the gold-standard for lumbar vertebrectomies, minimally invasive lateral approaches and a posterior-only approach are viable management strategies. Supplemental fixation is also required and may be achieved with anterior-only instrumentation, posterior-only instrumentation, and circumferential instrumentation. In the review to follow, an evidence-based approach will be used to outline appropriate indications, surgical technique, and concomitant reconstructive and stabilization options for lumbar corpectomies. The discussion to follow ideally will help optimize outcomes for patients treated with vertebral resection and lumbar corpectomies in the lumbar spine.

Adjustable Rigid Interspinous Process Fixation: A Biomechanical Study of Segmental Lordosis and Interbody Loading in the Lumbar Spine.

BackgroundRigid interspinous process fixation (ISPF) may serve as a minimally disruptive adjunct to lumbar interbody fusion. Previous biomechanical assessments of ISPF have demonstrated particularly advantageous outcomes in stabilizing the sagittal plane. However, ISPF has not been well characterized in regard to its impact on interbody load, which has implications for the risk of cage migration or subsidence, and sagittal alignment. The purpose of this study was to biomechanically assess in vitro the interbody load (IBL), focal lordosis (FL), and spinous process loading generated by in situ compression/distraction with a novel ISPF device capable of incremental in situ shortening/extension. Bilateral pedicle screw fixation (BPSF) was used as a control.MethodsTwo fresh frozen human lumbar spines were thawed and musculature was removed, leaving ligaments intact. Seven functional spinal units were iteratively tested, which involved a standard lateral discectomy, placement of a modified lateral cage possessing two load cells, and posterior fixation. BPSF and ISPF were performed at each level, with order of fixation was randomized. BPSF was first performed with maximum compressive exertion followed by 75% exertion to represent clinical application. The ISPF device was implanted at a neutral height and incrementally shortened/extended in situ in 1-mm increments. IBL and FL were measured under each condition. Loads on the spinous processes were estimated through bench-top mechanical calibration.ResultsNo significant differences in IBL were observed, but the ISPF device produced a significantly greater change in FL compared to the clinically relevant BPSF compression. IBL, as a function of ISPF device height, expressed linear behavior during compression and exponential behavior during distraction.ConclusionsThe novel ISPF device produced clinically effective IBL and FL, performing well in comparison to BPSF. Additionally, incremental ISPF device manipulation demonstrated predictable and clinically safe trends regarding loading of the interbody space and spinous processes.

Land Subsidence Susceptibility Mapping Using Bayesian, Functional, and Meta-Ensemble Machine Learning Models

To effectively prevent land subsidence over abandoned coal mines, it is necessary to quantitatively identify vulnerable areas. In this study, we evaluated the performance of predictive Bayesian, functional, and meta-ensemble machine learning models in generating land subsidence susceptibility (LSS) maps. All models were trained using half of a land subsidence inventory, and validated using the other half of the dataset. The model performance was evaluated by comparing the area under the receiver operating characteristic (ROC) curve of the resulting LSS map for each model. Among all models tested, the logit boost, which is a meta-ensemble machine leaning model, generated LSS maps with the highest accuracy (91.44%), i.e., higher than that of the other Bayesian and functional machine learning models, including the Bayes net (86.42%), naïve Bayes (85.39%), logistic (88.92%), and multilayer perceptron models (86.76%). The LSS maps produced in this study can be used to mitigate subsidence risk for people and important facilities within the study area, and as a foundation for further studies in other regions.

Clinical and radiologic outcomes of single-level direct lateral lumbar interbody fusion in patients with osteopenia

ObjectiveSubsidence of the interbody graft into the vertebral bodies is one of the major complications of direct lateral interbody fusion (DLIF), resulting in pseudoarthrosis and severe pain. Low bone mineral density (BMD) has been known to increase the risk of subsidence. This study aims to determine whether or not the osteopenia should influence the surgical results in DLIF surgery. MethodsWe retrospectively reviewed the data collected prospectively on all patients who underwent single-level DLIF at our institution. A total of 84 patients were included in this study, comprised of 41 in the osteopenia group and 43 in the normal BMD group. The clinical and radiologic characteristics were compared at preoperative and postoperative 1 and 2 years. ResultsAt postoperative two years, there was a statistically significant difference in disc height and intervertebral foramen height at index level between the two groups (p = 0.039, 0.044, respectively), but there was no significant difference in total lumbar lordosis (p = 0.179). At 24-month postoperative, 92.7% of the osteopenia group and 95.3% of the normal BMD group were solidly fused (p = 0.672). All postoperative clinical scores (VAS back pain, VAS leg pain, and ODI) improved similarly in both groups without significant difference. The overall incidence of cage subsidence with >3 mm was 17.1% in the osteopenia group and 9.3% in the normal BMD group (p = 0.345). ConclusionsPatients with osteopenia who undergo single-level DLIF combined with posterior fixation exhibited comparable clinical and radiological outcomes as patients with normal BMD.

Land subsidence hazard modeling: Machine learning to identify predictors and the role of human activities

Land subsidence caused by land use change and overexploitation of groundwater is an example of mismanagement of natural resources, yet subsidence remains difficult to predict. In this study, the relationship between land subsidence features and geo-environmental factors is investigated by comparing two machine learning algorithms (MLA): maximum entropy (MaxEnt) and genetic algorithm rule-set production (GARP) algorithms in the Kashmar Region, Iran. Land subsidence features (N = 79) were mapped using field surveys. Land use, lithology, the distance from traditional groundwater abstraction systems (Qanats), from afforestation projects, from neighboring faults, and the drawdown of groundwater level (DGL) (1991–2016) were used as predictive variables. Jackknife resampling showed that DGL, distance from afforestation projects, and distance from Qanat systems are major factors influencing land subsidence, with geology and faults being less important. The GARP algorithm outperformed the MaxEnt algorithm for all performance metrics. The performance of both models, as measured by the area under the receiver-operator characteristic curve (AUROC), decreased from 88.9–94.4% to 82.5–90.3% when DGL was excluded as a predictor, though the performance of GARP was still good to excellent even without DGL. MLAs produced maps of subsidence risk with acceptable accuracy, both with and without data on groundwater drawdown, suggesting that MLAs can usefully inform efforts to manage subsidence in data-scarce regions, though the highest accuracy requires data on changes in groundwater level.

Effect of Salinity on Silica Nanoparticle Adsorption Kinetics and Mechanisms for Fluid/Rock Interaction with Calcite.

This study addresses the kinetics of silica nanoparticle adsorption on calcite from a solution at three salinities: deionized water (DIW), synthetic seawater (SSW), and low salinity water (LSW). The nanoparticle adsorption mechanisms and the effects on calcite dissolution are addressed. It was shown that nanoparticle adsorption was best described with the second-order-kinetic model and that silica nanoparticle adsorption reduced calcite dissolution. This was confirmed by measuring the Ca2+ ion concentration, the pH, and by estimating the amount of calcite dissolved. This is an important conclusion of this work, especially as LSW as an enhanced oil recovery technique is a candidate for use in chalk fields. Less formation damage/dissolution of chalk when silica nanoparticles are combined with LSW can lower the risk of reservoir subsidence. Intraparticle diffusion and the pseudo-second-order models, indicated a reduction in the adsorption rate with increasing nanoparticle concentration in LSW. This is explained by possible repulsive forces among the nanoparticles as they diffuse from the bulk fluid onto the calcite surface. Ion charges reduce the repulsion among the nanoparticles through shielding. However, an increasing nanoparticle concentration reduces the shielding efficiency by the ions. Estimates of the surface forces confirmed that nanoparticle–mineral interaction is less attractive in LSW as compared to SSW and DIW.

Evaluation of Road Subsidence Risk from Model Chamber Tests

Evaluation of Road Subsidence Risk from Model Chamber Tests

The Effects of Bone Microstructure on Subsidence Risk for ALIF, LLIF, PLIF, and TLIF Spine Cages.

Several approaches (anterior, posterior, lateral, and transforaminal) are used in lumbar fusion surgery. However, it is unclear whether one of these approaches has the greatest subsidence risk as published clinical rates of cage subsidence vary widely (7-70%). Specifically, there is limited data on how a patient's endplate morphometry and trabecular bone quality influences cage subsidence risk. Therefore, this study compared subsidence (stiffness, maximum force, and work) between anterior (ALIF), lateral (LLIF), posterior (PLIF), and transforaminal (TLIF) lumbar interbody fusion cage designs to understand the impact of endplate and trabecular bone quality on subsidence. Forty-eight lumbar vertebrae were imaged with micro-ct to assess trabecular microarchitecture. micro-ct images of each vertebra were then imported into image processing software to measure endplate thickness (ET) and maximum endplate concavity depth (ECD). Generic ALIF, LLIF, PLIF, and TLIF cages made of polyether ether ketone were implanted on the superior endplates of all vertebrae and subsidence testing was performed. The results indicated that TLIF cages had significantly lower (p < 0.01) subsidence stiffness and maximum subsidence force compared to ALIF and LLIF cages. For all cage groups, trabecular bone volume fraction was better correlated with maximum subsidence force compared to ET and concavity depth. These findings highlight the importance of cage design (e.g., surface area), placement on the endplate, and trabecular bone quality on subsidence. These results may help surgeons during cage selection for lumbar fusion procedures to mitigate adverse events such as cage subsidence.

Field Experiment Report for Verification of Abandoned Lignite Mines by Robotic Exploration System

The risk of collapse and subsidence of abandoned lignite mines has been noted in the Tokai region of Japan. The cavity-filling process by local governments has been ongoing. There is no cavity map in the abandoned lignite mines, and it is necessary to understand and explore the underground space in order to estimate the amount of filling material needed. By request from Mitake-cho in Gifu Prefecture, we received the opportunity to explore the inside of an abandoned lignite mine using our robotic system. Prior to the exploration of the actual abandoned lignite mine, as a feasibility study, an experimental test field that simulated the elements of the abandoned lignite mine was prepared outdoors. Some experiments were performed and the robotic exploration system was evaluated in this study. This paper describes the lessons learned from the feasibility study.

Lateral lumbar interbody fusion in the elderly: a 10-year experience.

OBJECTIVEElderly patients, often presenting with multiple medical comorbidities, are touted to be at an increased risk of peri- and postoperative complications following spine surgery. Various minimally invasive surgical techniques have been developed and employed to treat an array of spinal conditions while minimizing complications. Lateral lumbar interbody fusion (LLIF) is one such approach. The authors describe clinical outcomes in patients over the age of 70 years following stand-alone LLIF.METHODSA retrospective query of a prospectively maintained database was performed for patients over the age of 70 years who underwent stand-alone LLIF. Patients with posterior segmental fixation and/or fusion were excluded. The preoperative and postoperative values for the Oswestry Disability Index (ODI) were analyzed to compare outcomes after intervention. Femoral neck t-scores were acquired from bone density scans and correlated with the incidence of graft subsidence.RESULTSAmong the study cohort of 55 patients, the median age at the time of surgery was 74 years (range 70-87 years). Seventeen patients had at least 3 medical comorbidities at surgery. Twenty-three patients underwent a 1-level, 14 a 2-level, and 18 patients a 3-level or greater stand-alone lateral fusion. The median estimated blood loss was 25 ml (range 5-280 ml). No statistically significant relationship was detected between volume of blood loss and the number of operative levels. The median length of hospital stay was 2 days (range 1-4 days). No statistically significant relationship was observed between the length of hospital stay and age at the time of surgery. There was one intraoperative death secondary to cardiac arrest, with a mortality rate of 1.8%. One patient developed a transient femoral nerve injury. Five patients with symptomatic graft subsidence subsequently underwent posterior instrumentation. A lower femoral neck t-score < -1.0 correlated with a higher incidence of graft subsidence (p = 0.006). The mean ODI score 1 year postoperatively of 31.1 was significantly (p = 0.003) less than the mean preoperative ODI score of 46.2.CONCLUSIONSStand-alone LLIF can be safely and effectively performed in the elderly population. Careful evaluation of preoperative bone density parameters should be employed to minimize risk of subsidence and need for additional surgery. Despite an association with increased comorbidities, age alone should not be a deterrent when considering stand-alone LLIF in the elderly population.

Analysis of Sewer Pipe Defect and Ground Subsidence Risk by Using CCTV and GPR Monitering Results

Analysis of Sewer Pipe Defect and Ground Subsidence Risk by Using CCTV and GPR Monitering Results

Morphological variability of the active Yellow River mouth under the new regime of riverine delivery

The Yellow River subaqueous delta (YRSD), once the most rapid depo-center among river deltas worldwide, has been under the risks of subsidence and degradation due to the new regime of riverine delivery affected by human interventions. Utilizing hydrologic and bathymetric surveying datasets, we examined the latest regime of river input from the perspective of water-sediment relationship, and the responding morphological evolutionary processes of active YRSD over a period of 20 years between 1996 and 2016. Results show that the new discharge regime is strongly interfered by the Water-Sediment Regulation Scheme (WSRS), characterized by a more drastic decline of sediment load than that of water discharge; more harmonious relationship between water and sediment discharges in the lower reach of the river to the sea; coarser sediment delivery and low suspended sediment concentration (SSC). We identified inverse erosion-accretion trends in the subaqueous region: net accretion of 0.15 m/yr in the active Yellow River mouth (AYRM) and severe erosion of −0.1 m/yr in the Gudong littoral zone (GDLZ). As the primary sink for sediment delivery, AYRM received approximately 68% of sediment delivery during the study period and sedimentation was mainly occurred in the shallower area where water depth was less than 10 m. In addition, recent morphological evolution of AYRM is found to have undergone through four stages, namely: moderate accretion (1996–2002), rapid accretion (2002–2007), reduced accretion (2007–2015) and rapid erosion (2015–2016). The new regime of riverine delivery presents multiple spatiotemporal scales in shaping deltaic morphology. Compared with the previous research, we present the morphological evolution of deltaic system over decadal timescale is strongly influenced by reduction of sediment supply derived from basin-scale human impacts, and the variability of subaqueous portion during the study period is closely related to inter-annual variability of river input. Besides, the building of AYRM is shaped by event-scale WSRS induced-floodwater, and decade-scale change of sediment pathway governed by frequent mouth channel migration. The results show, for the first time, that AYRM has experienced a significant erosion since the implementation of WSRS, with a decline of 99% sediment delivery in 2016 compared to the natural mode during 1950s. The results also indicate that to maintain the erosion-accretion balance of AYRM, an estimation of 41.4–62.3 Mt/yr sediment delivery should be kept. Due to the fluvial regime change from the natural to the highly human-regulated modes, the AYRM, as well as the whole YRSD, is expected to be transforming from the accretion to erosion states.

Cervical fusion cage computationally optimized with porous architected Titanium for minimized subsidence.

Anterior cervical discectomy with fusion is a common surgical treatment that can relieve patients suffering from cervical spondylosis. This surgery is most commonly performed with the use of a cervical cage. One serious complication of the fusion cages commercially available in the market is subsidence of the cage with loss of the normal alignment of the spine and recurrent pain. This work presents the proof-of-concept of a fusion cage made of a graded porous titanium with microarchitecture minimizing the risk of subsidence associated with fully-solid implants. The optimized properties of the porous implant are obtained through a scheme combining multiscale mechanics and density-based topology optimization. Asymptotic homogenization is used to capture the effective properties of the porous material, which uses a tetrahedron based cell as building block. The stress levels and normal strains obtained under various loading conditions on the C7 superior surface of the vertebrae are used as indicators of subsidence. The results suggest a reduced risk of subsidence for the optimized implant versus the fully-solid implant. Under the most severe condition of combined loading, a collective improvement of the average von Mises stress up to 14% can be observed on the posterior, left, and right lateral regions of the C7 superior surface. Similarly, for the average normal strain, the optimized cage exhibits a more favourable distribution with a top gain of 21.7% at given locations.

InSAR Reveals Land Deformation at Guangzhou and Foshan, China between 2011 and 2017 with COSMO-SkyMed Data

Subsidence from groundwater extraction and underground tunnel excavation has been known for more than a decade in Guangzhou and Foshan, but past studies have only monitored the subsidence patterns as far as 2011 using InSAR. In this study, the deformation occurring during the most recent time-period between 2011 and 2017 has been measured using COSMO-SkyMed (CSK) to understand if changes in temporal and spatial patterns of subsidence rates occurred. Using InSAR time-series analysis (TS-InSAR), we found that significant surface displacement rates occurred in the study area varying from −35 mm/year (subsidence) to 10 mm/year (uplift). The 2011–2017 TS-InSAR results were compared to two separate TS-InSAR analyses (2011–2013, and 2013–2017). Our CSK TS-InSAR results are in broad agreement with previous ENVISAT results and levelling data, strengthening our conclusion that localised subsidence phenomena occurs at different locations in Guangzhou and Foshan. A comparison between temporal and spatial patterns of deformations from our TS-InSAR measurements and different land use types in Guangzhou shows that there is no clear relationship between them. Many local scale deformation zones have been identified related to different phenomena. The majority of deformations is related to excessive groundwater extraction for agricultural and industrial purposes but subsidence in areas of subway construction also occurred. Furthermore, a detailed analysis on the sinkhole collapse in early 2018 has been conducted, suggesting that surface loading may be a controlling factor of the subsidence, especially along the road and highway. Roads and highways with similar subsidence phenomenon are identified. Continuous monitoring of the deforming areas identified by our analysis is important to measure the magnitude and spatial pattern of the evolving deformations in order to minimise the risk and hazards of land subsidence.

Stand-alone lumbar cage subsidence: A biomechanical sensitivity study of cage design and placement.

Background and objectiveSpinal degeneration and instability are commonly treated with interbody fusion cages either alone or supplemented with posterior instrumentation with the aim to immobilise the segment and restore intervertebral height. The purpose of this work is to establish a tool which may help to understand the effects of intervertebral cage design and placement on the biomechanical response of a patient-specific model to help reducing post-surgical complications such as subsidence and segment instability. MethodsA 3D lumbar functional spinal unit (FSU) finite element model was created and a parametric model of an interbody cage was designed and introduced in the FSU. A Drucker–Prager Cap plasticity formulation was used to predict plastic strains and bone failure in the vertebrae. The effect of varying cage size, cross-sectional area, apparent stiffness and positioning was evaluated under 500 N preload followed by 7.5 Nm multidirectional rotation and the results were compared with the intact model. ResultsThe most influential cage parameters on the FSU were size, curvature congruence with the endplates and cage placement. Segmental stiffness was higher when increasing the cross-sectional cage area in all loading directions and when the cage was anteriorly placed in all directions but extension. In general, the facet joint forces were reduced by increasing segmental stiffness. However, these forces were higher than in the intact model in most of the cases due to the displacement of the instantaneous centre of rotation. The highest plastic deformations took place at the caudal vertebra under flexion and increased for cages with greater stiffness. Thus, wider cages and a more anteriorly placement would increase the volume of failed bone and, therefore, the risk of subsidence. ConclusionsCage geometry plays a crucial role in the success of lumbar surgery. General considerations such as larger cages may be applied as a guideline, but parameters such as curvature or cage placement should be determined for each specific patient. This model provides a proof-of-concept of a tool for the preoperative evaluation of lumbar surgical outcomes.

Risk of subsidence and peri-prosthetic fractures using collared hydroxyapatite-coated stem for hip arthroplasty in the elderly.

Subsidence has been noted with both cemented and uncemented stems in hip arthroplasty. On most occasions, it's minimal (i.e. less than 2 mm) and stabilises at 1 year. However, when its progressive and significant, it causes loss of length and horizontal offset, and when symptomatic warrants a revision. A retrospective radiological review of the patient database was carried out to identify all patients with age ≥ 70 years who underwent elective hip arthroplasty using uncemented HA coated collared stem and had radiographs at 1 year follow up. A total of 176 patients were identified from January 2009 to June 2010. 2 independent investigators classified the proximal femur based on Dorr type and calculated the subsidence based on Engh and Massin method of calculating the distance between the tip of greater trochanter and shoulder of the prosthesis. 7 patients (4 Bs, 2 As, 1 C) had a subsidence of ≥ 2 mm (2-3.2 mm) at 1 year. None of them was symptomatic. 1 of them was secondary to a missed calcar crack and continued to subside for 9 mm before it stabilised on the lesser trochanter at 4 years follow up. There were Dorr 22 (12.5%) type A, 147(83.5%) type B and 7(4%) type C. The mean age was 77.4 years (70-91 years) and male: female ratio was 7:15. 3 patients had an intraoperative calcar crack requiring cabling. All were mobilised full weight-bearing postoperatively, and none had a subsidence of >2 mm at 1 year follow-up. Our subgroup analysis identified that subsidence can happen when the collar is "non-functional" and the initial press fit of the stem wasn't achieved. It can also occur in an event of calcar crack, which is missed intraoperatively. In cases of calcar crack which went on to have to cable during the primary procedure, it neither changed the post-operative rehabilitation nor did it show an increased risk of subsidence. A fully hydroxyapatite (HA) coated collared stem, when used in elderly age group for elective THR, has only 2% risk of intraoperative periprosthetic fracture. There's a 4% risk of radiologically significant subsidence (i.e. ≥2 mm), however, it has not proven to be clinically significant in our study. Dorr canal type had no bearing on either risk of periprosthetic fracture or subsidence. Collared stems did not have a statistically significant difference in risk of subsidence and peri-prosthetic fracture in comparison to un-collared stem, although there was a non-significant trend in favour of collar use.

Discovery of ancient Roman "highway" reveals geomorphic changes in karst environments during historic times.

Sinkholes are a well-known geologic hazard but their past occurrence, useful for subsidence risk prediction, is difficult to define, especially for ancient historic times. Consequently, our knowledge about Holocene carbonate landscapes is often limited. A multidisciplinary study of Trieste Karst (Italy), close to early Roman military fortifications, led to the identification of possible ancient road tracks, cut by at least one sinkhole. Electrical Resistivity Tomography through the sinkhole has suggested the presence of a cave below its bottom, possibly responsible of the sinkhole formation, while Ground Penetrating Radar has detected no tectonic disturbances underneath the tracks. Additionally, archaeological surveys led to the discovery of over 200 Roman shoe hobnails within or close to the investigated route. According to these data, the tracks are interpreted as the remains of a main Roman road, whose itinerary has been reconstructed for more than 4 km together with other elements of ancient landscape. Our results provide the first known evidence of a Roman main road swallowed by sinkholes and suggest that Holocene karst landscapes could be much different from what previously believed. In fact, sinkholes visible nowadays in the investigated region could have been flat areas filled by sediments up to the Roman time.

Biomechanical analysis of lumbar interbody fusion cages with various lordotic angles: a finite element study

Inappropriate lordotic angle of lumbar fusion cage could be associated with cage damage or subsidence. The biomechanical influence of cage lordotic angle on lumbar spine has not been fully investigated. Four surgical finite element models were constructed by inserting cages with various lordotic angles at L3-L4 disc space. The four motion modes were simulated. The range of motion (ROM) decreased with increased lordotic angle of cage in flexion, extension, and rotation, whereas it was not substantially changed in bending. The maximum stress in cage decreased with increased lordotic angle of cage in all motion modes. The maximum stress in endplate at surgical level increased with increased lordotic angle of cage in flexion and rotation, whereas it was not substantially changed in extension and bending. The facet joint force (FJF) was much smaller than that for the intact conditions in extension, bending, and rotation, while it was not substantially changed in flexion. In conclusion, the ROM, stresses in the cage and endplate at surgical level are sensitive to the lordotic angle of cage. The increased cage lordotic angle may provide better stability and reduce the risk of cage damage, whereas it may increase the risk of subsidence in flexion and rotation.

Safety of a novel modular cage for transforaminal lumbar interbody fusion - clinical cohort study in 20 patients with degenerative disc disease.

Introduction: Transforaminal lumbar interbody fusion (TLIF) is used to reconstruct disc height and reduce degenerative deformity in spinal fusion. Patients with osteoporosis are at high risk of TLIF cage subsidence; possibly due to the relatively small footprint compared to anterior interbody devices. Recently, modular TLIF cage with an integral rail and slot system was developed to reduce cage subsidence and allow early rehabilitation.Objective: To study the safety of a modular TLIF device in patients with degenerative disc disorders (DDD) with regard to surgical complications, non-union, and subsidence.Methods: Patients with DDD treated with a modular TLIF cage (Polyetheretherketone (PEEK), VTI interfuse S) were analysed retrospectively with one-year follow-up. Lumbar sagittal parameters were collected preoperatively, postoperatively and at one year follow-up. Cage subsidence, fusion rate, screw loosening and proportion of endplate coverage were assessed in computed tomography scan.Results: 20 patients (age 66 ± 10 years, 65% female, BMI 28 ± 5 kg/m2) with a total of 37 fusion levels were included. 15 patients had degenerative spondylosis and 5 patients had degenerative scoliosis. The cages covered >60% of the vertebral body diameters. Lumbar lordosis angle and segmental disc angle increased from 45.2 ± 14.5 and 7.3 ± 3.6 to 52.7 ± 9.1 and 10.5 ± 3.5 (p = 0.029 and 0.0002) postoperatively for each parameter respectively without loss of correction at one year follow up. One case of deep postoperative infection occurred (5%). No cage subsidence occurred. No non-union or screw loosening occurred.Conclusions: The modular TLIF cage was safe with regard to subsidence and union-rate. It restored and maintained lumbar lordosis angle, segmental disc angle and disc height, which can be attributed to the large footprint of this modular cage.