Electron-hole separation in ferroelectric oxides for efficient photovoltaic responses.

Despite their potential to exceed the theoretical Shockley-Queisser limit, ferroelectric photovoltaics (FPVs) have performed inefficiently due to their extremely low photocurrents. Incorporating Bi2FeCrO6 (BFCO) as the light absorber in FPVs has recently led to impressively high and record photocurrents [Nechache R, et al. (2015) Nat Photonics 9:61-67], which has revived the FPV field. However, our understanding of this remarkable phenomenon is far from satisfactory. Here, we use first-principles calculations to determine that such excellent performance mainly lies in the efficient separation of electron-hole (e-h) pairs. We show that photoexcited electrons and holes in BFCO are spatially separated on the Fe and Cr sites, respectively. This separation is much more pronounced in disordered BFCO phases, which adequately explains the observed exceptional PV responses. We further establish a design strategy to discover next-generation FPV materials. By exploring 44 additional Bi-based double-perovskite oxides, we suggest five active-layer materials that offer a combination of strong e-h separations and visible-light absorptions for FPV applications. Our work indicates that charge separation is the most important issue to be addressed for FPVs to compete with conventional devices.

First-Principles Investigations to Evaluate the Spin-Polarized Metal-to-Insulator Transition of Halide Cuprite Perovskites for Smart Windows.

Although smart windows have received wide attention as energy-saving devices, conventional metal-to-insulator materials such as VO2 hinder their commercial usage because of their high transition temperature and low solar energy modulation. Further development can be achieved by finding a new material system that can effectively overcome these limitations. In this study, first-principles density functional theory calculations are used to investigate the possibility of exploiting a spin-polarized band gap material for smart window applications. Halide cuprite perovskites (A2CuX4) were chosen because they have a spin-polarized band gap that can be tuned by element selection at sites A and X. Our study shows that the optical transmittance of the insulating phase is increased by a violation of the selection rule. The spin-polarized band gap is closely related to the metal-to-insulator transition temperature and can be modulated by chemical engineering, strain engineering, or both. Therefore, A2CuX4 is a promising candidate for smart windows.

Boosting-Crystal Graph Convolutional Neural Network for Predicting Highly Imbalanced Data: A Case Study for Metal-Insulator Transition Materials.

Applying machine-learning techniques for imbalanced data sets presents a significant challenge in materials science since the underrepresented characteristics of minority classes are often buried by the abundance of unrelated characteristics in majority of classes. Existing approaches to address this focus on balancing the counts of each class using oversampling or synthetic data generation techniques. However, these methods can lead to loss of valuable information or overfitting. Here, we introduce a deep learning framework to predict minority-class materials, specifically within the realm of metal-insulator transition (MIT) materials. The proposed approach, termed boosting-CGCNN, combines the crystal graph convolutional neural network (CGCNN) model with a gradient-boosting algorithm. The model effectively handled extreme class imbalances in MIT material data by sequentially building a deeper neural network. The comparative evaluations demonstrated the superior performance of the proposed model compared to other approaches. Our approach is a promising solution for handling imbalanced data sets in materials science.

First-Principles Investigations on the Semiconductor-to-Metal Phase Transition of 2D Si2Te3 for Reversible Resistive Switching.

Si2Te3 is attracting attention due to its compatibility with Si technology while still showing advantages as a two-dimensional layered material. Although recent experimental studies have observed the resistive switching process in Si2Te3-based memristors, the mechanism has not been clearly identified. In this study, first-principles density functional theory calculations are employed to understand the relationship between the phase transition of Si2Te3 and the reversible resistive switching of the Si2Te3-based memristor. Our calculation results show that although semiconducting Si2Te3 is energetically more stable than two metallic Si2Te3 phases (α and ß), two metallic Si2Te3 can be energetically stabilized by excess holes. The enhanced energetic preference of two metallic Si2Te3 by excess holes is explained by the reduced occupation of antibonding states between Si and Te. Our study finds that the energy barrier for the phase transition between semiconducting Si2Te3 and α-metallic Si2Te3 varies significantly by excess charge carriers so the phase transition can be directly connected to the reversible resistive switching of the Si2Te3-based memristor under external bias. Our finding will serve as a cornerstone for optimizing the resistive switching process of the Si2Te3-based memristor.

Cooperative coupling of anisotropic phonon modes intensifies visible thermochromism in layered α-MoO3.

Applications that provide versatile, high temperature warnings require the development of thermochromic materials based on solid-state oxides. To boost the visible thermochromic properties, a fundamental approach to reveal the unclear roles of local structure on band structure modulation should be considered by scrutinizing the thermal motion of phonon modes. Herein, we demonstrate that selective coupling of intra-layer phonon modes intensifies the visible thermochromism of layered oxides α-MoO3. As a result of thermally induced band gap reduction in α-MoO3, the observed color reversibly changes from white at 25 °C to yellow at 300 °C owing to a red shift of the absorption edge with an increase of temperature. This high-temperature thermochromism is attributed to the anisotropic change of layered α-MoO3 crystal structures characterized by synchrotron X-ray diffraction. Notably, quantitative characterizations combined with theoretical calculations reveal that the cooperative coupling of active Raman modes in intra-layer [MoO6] octahedra are responsible for the band gap reduction at high temperature; this defies the general belief regarding the origin of visible thermochromism in layered oxides as the modulation of a van der Waals inter-layer distance. These original results can aid the development of a new strategy to further intensify high-temperature thermochromism by anion doping for highly sensitive temperature-indicating applications.

Highly Stable Germanium Microparticle Anodes with a Hybrid Conductive Shell for High Volumetric and Fast Lithium Storage.

The ability to realize a highly capacitive/conductive electrode is an essential factor in large-scale devices, requiring a high-power/energy density system. Germanium is a feasible candidate as an anode material of lithium-ion batteries to meet the demands. However, the application is constrained due to low charge conductivity and large volume change on cycles. Here, we design a hybrid conductive shell of multi-component titanium oxide on a germanium microstructure. The shell enables facile hybrid ionic/electronic conductivity for swift charge mobility in the germanium anode, revealed through computational calculation and consecutive measurement of electrochemical impedance spectroscopy. Furthermore, a well-constructed electrode features a high initial Coulombic efficiency (90.6%) and stable cycle life for 800 cycles (capacity retention of 90.4%) for a fast-charging system. The stress-resilient properties of dense microparticle facilitate to alleviate structural failure toward high volumetric (up to 1737 W h L-1) and power density (767 W h L-1 at 7280 W L-1) of full cells, paired with highly loaded NCM811 in practical application.

Dural tears in percutaneous endoscopic lumbar discectomy.

The objective of the study was to demonstrate the clinical characteristics of dural tears during percutaneous endoscopic lumbar discectomy (PELD) and to discuss how to prevent this unintended complication. The study used data from 816 consecutive patients who underwent PELD between 2003 and 2007. A total of nine patients (1.1%) experienced symptomatic dural tears. The clinical outcomes were evaluated using the visual analogue scale (VAS), the Oswestry disability index (ODI), and modified MacNab criteria. Intractable radicular pain was the most common symptom, while classical manifestations, such as CSF leakage or wound swelling, were rare. In three of the nine cases, the dural tears were detected intraoperatively, while the remaining six cases were not recognized during the procedure. Among the unrecognized patients, two patients were found with nerve root herniation causing profound neurological deficits. All patients were managed by secondary open repair surgeries. The mean follow-up period was 30.8 months. The mean VAS of radicular leg pain improved from 8.3 to 2.6, and that of back pain improved from 4.1 to 2.6. The mean ODI improved from 69.6 to 29.2%. The final outcomes were excellent in one, good in five, fair in one, and poor in two patients. As application of the endoscopic procedure has been broadened to more complex cases, the risk of dural tears may increase. Unrecognized dural tear with nerve root herniation may cause permanent neurological sequelae. Accurate information and proper technical considerations are essential to prevent this unpredictable complication.

A-Site Effect on the Oxidation Process of Sn-Halide Perovskite: First-Principles Calculations.

Tin-halide perovskite solar cells (Sn-PSCs) are promising candidates as an alternative to toxic lead-halide PSCs. However, Sn2+ is easily oxidized to Sn4+, so Sn-PSCs are unstable in air. Here, we use first-principles density functional theory calculations to elucidate the oxidation process of Sn2+ at the surface of ASnBr3 [A = Cs or CH3NH3 (MA)]. Regardless of the A-site cation, adsorption of O2 leads to the formation of SnO2, which creates a Sn vacancy at the surface. The A-site cation determines whether the created vacancies are stabilized in the bulk or at the surface. For CsSnBr3, the Sn vacancy is stabilized at the surface, so further oxidation is limited. For MASnBr3, the Sn vacancy moves into bulk region, so additional Sn is supplied to the surface; as a result, a continuous oxidation process can occur. The stabilization of Sn vacancy is closely related to the polarization that the A-site cation causes in the system.

Spinal cord glioblastoma multiforme of conus medullaris masquerading as high lumbar disk herniation.

BACKGROUND: A case of primary intramedullary glioblastoma occurring at conus medullaris is presented, which was initially undetected and misdiagnosed as L1 through L2 disk herniation. CASE DESCRIPTION: After the performance of L1 through L2 discectomy, the patient's initial painful symptom did not subside. The patient then developed a progressive paraparesis. The outside surgeons only predicted the possibility of reherniation or hematoma collection at the former operated level as the diagnosis for the paraparesis. After the patient was transferred to our hospital and after a thorough review of initial and follow-up magnetic resonance imaging with enhancement before second operation, an enlarged conus medullaris with mixed signal intensity was noted without evidence of re-herniation or hematoma collection. The patient underwent reoperation with biopsy of the intramedullary lesion, which was histologically confirmed as primary glioblastoma. CONCLUSION: Careful neurologic and radiologic evaluations should precede before any decision of surgical intervention as intramedullary and degenerative pathologies may coexist in the upper lumbar spine.

Transforaminal percutaneous endoscopic lumbar discectomy for upper lumbar disc herniation: clinical outcome, prognostic factors, and technical consideration.

BACKGROUND: Compared with lower lumbar disc herniations, upper lumbar disc herniations at L1-L2 and L2-L3 have specific characteristics that result in different surgical outcomes after conventional open discectomy. There are no published studies on the feasibility of percutaneous endoscopic lumbar discectomy for upper lumbar disc herniation. The purpose of this study was to assess the clinical outcome, prognostic factors and the technical pitfalls of PELD for upper lumbar disc herniation. METHOD: Forty-five patients with a soft disc herniation at L1-L2 or L2-L3 underwent percutaneous endoscopic discectomy. Posterolateral transforaminal endoscopic laser-assisted disc removal was performed under local anesthesia. Clinical outcomes was assessed using the Prolo scale. The prognostic factors associated with outcome were then analyzed. FINDINGS: The mean follow-up was 38.8 months (range, 25-52 months). The outcome of the 45 patients was excellent in 21 (46.7%), good in 14 patients (31.1%), fair in six patients (13.3%), and poor in four patients (8.9%). Four patients with a poor outcome underwent further open surgery. Mean scores on a visual analog scale decreased from 8.38 to 2.36 (P < 0.0001). Age less than 45 years and a lateral disc herniation were independently associated with an excellent outcome (P < 0.05). CONCLUSIONS: Patient selection and an anatomically modified surgical technique promote a more successful outcome after percutaneous endoscopic discectomy for upper lumbar disc herniation.

Postoperative retroperitoneal hematoma following transforaminal percutaneous endoscopic lumbar discectomy.

OBJECT: The purpose of this study was to demonstrate the clinical characteristics of postoperative retroperitoneal hematoma (RPH) following transforaminal percutaneous endoscopic lumbar discectomy (PELD) and to discuss how to prevent the complication of unintended hemorrhage. METHODS: The medical records of 412 consecutive patients treated with transforaminal PELD between January 2005 and May 2007 were reviewed. A total of 4 patients (0.97%) experienced symptomatic postoperative RPH. The clinical outcomes were evaluated using the visual analog scale and the Oswestry Disability Index. RESULTS: The common symptom in all patients with a hematoma was inguinal pain. The mean hematoma volume was 527.9 ml (range 53.3-1274.1 ml). Two patients with massive diffuse-type RPHs compressing the intraabdominal structures required open hematoma evacuation performed by general surgeons, and the other 2 patients with small, localized RPHs of < 100 ml were treated conservatively. The mean follow-up period was 21.3 months (range 13-29 months). The mean visual analog scale score for radicular leg pain improved from 7.6 to 1.8 and that for back pain improved from 4.3 to 2. The mean Oswestry Disability Index improved from 58.8 to 9.1%. The preoperative symptoms improved after the second treatment without significant neurological sequelae in all patients. CONCLUSIONS: Although transforaminal PELD is a minimally invasive and safe procedure, the possibility of RPH should be kept in mind. Adequate technical and anatomical considerations are important to avoid this unusual hemorrhagic complication, especially in the patient with underlying medical problems or previous operative scarring. A high index of suspicion and early detection is also important to avoid the progression of the hematoma.

Predictive factors for subsequent vertebral fracture after percutaneous vertebroplasty.

OBJECT: The purpose of this study was to evaluate the predictive factors for subsequent vertebral fracture occurring after percutaneous vertebroplasty (PVP) at the neighboring levels (adjacent vs nonadjacent levels). METHODS: The medical records of 508 consecutive patients treated with PVP between January 2000 and December 2002 were retrospectively reviewed. A total of 45 patients with 49 painful vertebral fractures occurring after PVP was identified based on clinical and radiological findings. New vertebral fractures, developing at any of the 3 consecutive vertebral bodies (VBs) above or below the previously treated level, were the focus of the study. The patients were divided into 3 groups: an adjacent-level fracture group, nonadjacent-level fracture group, and a control group composed of 50 randomly selected patients in whom there was no evidence of a new fracture. Clinical, imaging, and procedure-related factors for each group were statistically analyzed. RESULTS: In 31 patients 35 VBs were classified as adjacent-level fractures, and in 14 patients 14 VBs were classified as nonadjacent-level fractures. After further vertebroplasty, the overall pain intensity and satisfaction rate in patients with post-PVP fractures were similar to those in the control group. In cases involving adjacent fractures, lower body mass index and intradiscal cement leakage were the significant predictive factors of fracture. In contrast, lower mobility of the index segment was related to nonadjacent-level fracture. CONCLUSIONS: According to the authors' results, the mechanisms of subsequent fracture at adjacent and nonadjacent vertebrae are different. A direct pillar effect (that is, the difference in strength caused by cement augmentation) may provoke an adjacent-level fracture, whereas a dynamic hammer effect (the difference in segmental mobility) may lead to a nonadjacent fracture.

Laser-assisted anterior cervical corpectomy versus posterior laminoplasty for cervical myelopathic patients with multilevel ossification of the posterior longitudinal ligament.

OBJECTIVE: This study reports on the comparative results of a series of patients with multilevel cervical ossification of the posterior longitudinal ligament (OPLL) who were treated with laser-assisted anterior corpectomy or laminoplasty. METHODS: Forty-eight patients (21 patients with anterior corpectomy and 27 patients with laminoplasty) with cervical OPLL involvement of three or more vertebral bodies were retrospectively reviewed. Both pre- and postoperatively neurological status was graded according to the Nurick grading system. The anteroposterior (AP) diameter change at the narrowest part of the spinal canal, the change in the regional and the overall cervical Cobb's angle, and the change in cervical range of motion (ROM) were all measured. The mean follow-up periods were 21.8 mo and 29.1 mo for the corpectomy and laminoplasty patients, respectively. RESULTS: The mean changes in the pre- to postoperative Nurick grades were 1.9 for the corpectomy group and 1 for the laminoplasty group (p < 0.05). The mean changes in the pre- to postoperative spinal canal AP diameters were 9.1 mm and 4.11 mm, respectively, for the corpectomy group and the laminoplasty group (p < 0.05). The mean changes of the regional Cobb's angle were 1.7 degrees and -3.1 degrees (p = 0.06), and the mean changes of the overall cervical Cobb's angle were 1.1 degrees and -1.6 degrees , respectively, for the corpectomy group and the laminoplasty group (p > 0.05). The changes in the cervical degree of ROM were -19.6 degrees and -19.7 degrees , respectively, for the corpectomy group and the laminoplasty group (p > 0.05). CONCLUSIONS: Direct decompression of the spinal cord by laser-assisted anterior cervical corpectomy was shown to be a better surgical option on long-term follow-up, yielding more recovery of neurological deficits, achieving adequate decompression of the spinal canal, and preventing the development of regional kyphosis at the operated level of the spine, in patients with multilevel cervical OPLL.

Use of diffusion tensor imaging to evaluate weakness.

OBJECT: Recently, diffusion tensor (DT) imaging was introduced to demonstrate white matter tracts. However, research interest has focused on the anatomical rather than the functional aspects of this imaging modality. The authors undertook a functional analysis of DT imaging to determine the relationship between weakness and changes on DT images. METHODS: Diffusion tensor images were obtained in 23 patients with lesions located adjacent to the pyramidal tract. Patients were classified according to their motor deficit. Axial magnetic resonance image sections through the maximum tumor diameters were selected and the mean apparent diffusion coefficients (ADCs) and mean fractional anisotropies (FAs) were measured. One ovoid region of interest (ovROI) was placed in the center of the pyramidal tract and another was designed to include the whole pyramidal tract at the same axial level (wROI). To determine intraobserver variability, a single neurosurgeon measured mean ADCs and FAs four times by using these two different ROI types without knowledge of any clinical information. To determine interobserver variability, a second neurosurgeon who was also unaware of any clinical information measured the mean ADCs and FAs by using the wROI method. The five measurements produced the same results. The mean FA at the lesion side of the pyramidal tract was significantly lower in patients with weakness (p < 0.01). Little intraobserver measurement variability occurred using the ovROI method, and no interobserver variability occurred using the wROI method. CONCLUSIONS: Motor weakness was significantly related to a low mean FA in the pyramidal tract on the lesion side. Designing an ROI that includes the whole pyramidal tract is an easier and more reproducible method than using an ovROI method.

Anterior minimally invasive approaches for the cervical spine.

The percutaneous endoscopic discectomy (PECD) with working channel endoscope (WSH) endoscopy set could be a safe and effective minimally invasive surgical option for non-contained cervical disc herniation in selected patients. Judicious use of the end-firing Ho: Yttrium-Aluminium-Garnet (YAG) laser for both decompressive and thermoannuloplasty effect during the percutaneous endoscopic cervical annuloplasty (PECA) is mandatory in order to prevent possible injury to spinal cord or root. Although the percutaneous cervical stabilization (PCS) using the cervical B-Twin may not completely replace the cervical arthrodesis, this minimally invasive procedure can preserve anterior structures and thereby retain segmental stability and prevent the possible kyphotic progression after fusion surgery. To our knowledge, these minimally invasive procedures for cervical spine disease may serve to minimize surgery-induced complications associated with anterior cervical discectomy and fusion (ACDF).

The nature of hydrogen-bonding interaction in the prototypic hybrid halide perovskite, tetragonal CH3NH3PbI3.

In spite of the key role of hydrogen bonding in the structural stabilization of the prototypic hybrid halide perovskite, CH3NH3PbI3 (MAPbI3), little progress has been made in our in-depth understanding of the hydrogen-bonding interaction between the MA(+)-ion and the iodide ions in the PbI6-octahedron network. Herein, we show that there exist two distinct types of the hydrogen-bonding interaction, naming α- and ß-modes, in the tetragonal MAPbI3 on the basis of symmetry argument and density-functional theory calculations. The computed Kohn-Sham (K-S) energy difference between these two interaction modes is 45.14 meV per MA-site with the α-interaction mode being responsible for the stable hydrogen-bonding network. The computed bandgap (Eg) is also affected by the hydrogen-bonding mode, with Eg of the α-interaction mode (1.73 eV) being significantly narrower than that of the ß-interaction mode (2.03 eV). We have further estimated the individual bonding strength for the ten relevant hydrogen bonds having a bond critical point.

A Biomechanical Analysis of an Artificial Disc With a Shock-absorbing Core Property by Using Whole-cervical Spine Finite Element Analysis.

STUDY DESIGN: A biomechanical comparison among the intact C2 to C7 segments, the C5 to C6 segments implanted with fusion cage, and three different artificial disc replacements (ADRs) by finite element (FE) model creation reflecting the entire cervical spine below C2. OBJECTIVE: The aim of this study was to analyze the biomechanical changes in subaxial cervical spine after ADR and to verify the efficacy of a new mobile core artificial disc Baguera C that is designed to absorb shock. SUMMARY OF BACKGROUND DATA: Scarce references could be found and compared regarding the cervical ADR devices' biomechanical differences that are consequently related to their different clinical results. METHODS: One fusion device (CJ cage system, WINNOVA) and three different cervical artificial discs (Prodisc-C Nova (DePuy Synthes), Discocerv (Scient'x/Alphatec), Baguera C (Spineart)) were inserted at C5-6 disc space inside the FE model and analyzed. Hybrid loading conditions, under bending moments of 1 Nm along flexion, extension, lateral bending, and axial rotation with a compressive force of 50 N along the follower loading direction, were used in this study. Biomechanical behaviors such as segmental mobility, facet joint forces, and possible wear debris phenomenon inside the core were investigated. RESULTS: The segmental motions as well as facet joint forces were exaggerated after ADR regardless of type of the devices. The Baguera C mimicked the intact cervical spine regarding the location of the center of rotation only during the flexion moment. It also showed a relatively wider distribution of the contact area and significantly lower contact pressure distribution on the core than the other two devices. A "lift off" phenomenon was noted for other two devices according to the specific loading condition. CONCLUSION: The mobile core artificial disc Baguera C can be considered biomechanically superior to other devices by demonstrating no "lift off" phenomenon, and significantly lower contact pressure distribution on core. LEVEL OF EVIDENCE: N/A.

Hydrogen-doped Brookite TiO2 Nanobullets Array as a Novel Photoanode for Efficient Solar Water Splitting.

As a representative photocatalyst for photoelectrochemical solar water splitting, TiO2 has been intensively studied but most researches have focused on the rutile and anatsase phases because brookite, another important crystalline polymorph of TiO2, rarely exists in nature and is difficult to synthesize. In this work, hydrogen doped brookite (H:brookite) nanobullet arrays were synthesized via a well-designed solution reaction for the first time. H:brookite shows highly improved PEC properties with excellent stability, enhanced photocurrent, and significantly high Faradaic efficiency for overall solar water splitting. To support the experimental data, ab initio density functional theory calculations were also conducted. At the interstitial doping site that has minimum formation energy, the hydrogen atoms act as shallow donors and exist as H+. which has the minimum formation energy among three states of hydrogen (H+. H0, and H-). The calculated density of states of H:brookite shows a narrowed bandgap and an increased electron density compared to the pristine brookite. The combined experimental and theoretical results provide frameworks for the exploration of the PEC properties of doped brookite and extend our knowledge regarding the undiscovered properties of brookite of TiO2.

Clinical significance of achieving a flexion limitation with a tension band system in grade 1 degenerative spondylolisthesis: a minimum 5-year follow-up.

STUDY DESIGN: Retrospective clinical study. OBJECTIVE: To evaluate the effect of the limitation of flexion rotation clinically and radiologically after interspinous soft stabilization using a tension band system in grade 1 degenerative spondylolisthesis. SUMMARY OF BACKGROUND DATA: Although several studies have been published on the clinical effects of limiting rotatory motion using tension band systems, which mainly targets the limitation of flexion rather than that of extension, they were confined to the category of pedicle screw-based systems, revealing inconsistent long-term outcomes. METHODS: Sixty-one patients with a mean age of 60.6 years (range, 28-76 yr) who underwent interspinous soft stabilization after decompression for grade 1 degenerative spondylolisthesis with stenosis between 2002 and 2004 were analyzed. At follow-up, the patients were divided into 2 groups on the basis of their achievement or failure to achieve flexion limitation. The clinical and radiological findings were analyzed. A multiple linear regression analysis was performed to determine the prognostic factors for surgical outcomes. RESULTS: At a mean follow-up duration of 72.5 months (range, 61-82 mo), 51 patients were classified into the flexion-limited group and 10 into the flexion-unlimited group. Statistically significant improvements were noted only in the flexion-limited group in all clinical scores. In the flexion-unlimited group, there were significant deteriorations in flexion angle (P = 0.009), axial thickness of the ligamentum flavum (P = 0.013), and the foraminal cross-sectional area (P = 0.011), resulting in significant intergroup differences. The preoperative extension angle was identified as the most influential variable for the flexion limitation and the clinical outcomes. CONCLUSION: The effects of the limitation of flexion rotation achieved through interspinous soft stabilization using a tension band system after decompression were related to the prevention of late recurrent stenosis and resultant radicular pain caused by flexion instability. The extension potential at the index level was recognized as a major prognostic factor that can predict the flexion limitation and the clinical results. LEVEL OF EVIDENCE: 4.

Unsuccessful percutaneous endoscopic lumbar discectomy: a single-center experience of 10,228 cases.

BACKGROUND: Percutaneous endoscopic lumbar discectomy (PELD) has remarkably evolved with successful results. Although PELD has gained popularity for the treatment of herniated disc (HD), the risk of surgical failure may be a major obstacle to performing PELD. We analyzed unsuccessful cases requiring reoperation. OBJECTIVE: To find common causes of surgical failure and elucidate the limitations of the conventional PELD technique. METHODS: A retrospective review was performed on all patients who had undergone PELD between January 2001 and December 2012. Unsuccessful PELD was defined as a case requiring reoperation within 6 weeks after primary surgery. Chart review was done, and preoperative, intraoperative, and postoperative radiographic reviews were performed. All unsuccessful PELD cases were classified according to the type of HD, location of herniation, extruded disc migration, working channel position, and intraoperative and postoperative findings. RESULTS: In 12 years, 10,228 patients had undergone PELD; 436 (4.3%) cases were unsuccessful. The causes were incomplete removal of HDs in 283 patients (2.8%), recurrence in 78 (0.8%), persistent pain even after complete HD removal in 41 (0.4%), and approach-related pain in 21 (0.2%). Incomplete removal of the HD was caused by inappropriate positioning (95 cases; 33.6%) of the working channel and occurred in central HDs (91 cases; 32.2%), migrated HDs (70 cases; 24.7%), and axillary type HDs (63 cases; 22.3%). CONCLUSION: Proper surgical indications and good working channel position are important for successful PELD. PELD techniques should be specifically designed to remove the disc fragments in various types of HD.