Fusion Area Research Articles

Numerical analysis of heat transfer and fluid flow characteristics and their influence on bead defects formation in oscillating laser-GMA hybrid welding of lap joints

In this study, the accuracy of the model developed for oscillating laser-GMA hybrid welding has been improved by integrating more experimentally measured parameters, such as the droplet velocity, transient arc power, and fusion area on sheets at the transverse cross-section. The effects of lateral distance of hybrid heat source relative to the top sheet edge on heat transfer and fluid flow in weld pool are numerically simulated. It is found that with more offset of the hybrid heat source to the top sheet, a larger depression and stronger lateral flow occur in weld pool, which leads to a delayed and weak backwards flow. These characteristics of heat transfer and fluid flow play a great role in the formation of weld bead defects of lap joint configuration, such as irregularity, discontinuity, lack of fusion at the top sheet. Compared to the experimental investigation, the numerical simulation provides not only quantitative description of the occurrence of those weld bead defects but also a deep physical insight into the whole process. Thus, it is useful for the parameter optimizations and further applications of this hybrid welding process.

Early development of the human dentition revisited.

In this review, classical data on the early steps in human odontogenesis are summarized and updated with specific insights into the development of the upper and lower embryonic jaws to help in understanding some oral pathologies. The initial step of human odontogenesis is classically characterized by two parallel horseshoe‐shaped epithelial laminae. These originate from the oral epithelium and an ingrowth into the jaw mesenchyme: the internal dental lamina gives rise to deciduous tooth primordia, while the external vestibular lamina represents the developmental base of the oral vestibule. However, a more complex situation was revealed by recent studies combining analyses of the dental and adjacent oral epithelia on histological sections and computer‐aided three‐dimensional (3D) reconstructions during the 2nd month of human embryonic development. The dental epithelium forms a mound, where swellings appear later, corresponding to the individual primordia of deciduous teeth. External to the developing deciduous dentition, the 3D reconstructions do not show any continuous vestibular lamina but instead a complex of discontinuous epithelial bulges and ridges. The patterns of these epithelial structures and their relationship to the dental epithelium differ not only between the upper and lower jaws but also between the lip and cheek segments in each jaw. Knowledge of early odontogenesis may help in understanding some oral pathologies. For example, the human lateral incisor has a dual origin: it arises in the area of fusion between the medial nasal and maxillary facial processes and involves material from these two regions. Such a dual origin at the site of fusion of facial processes represents a predisposition to developmental vulnerability for the upper lateral incisor, resulting in its frequent anomalies (absence, hypoplasia, duplication), especially in patients with a cleft lip and/or jaw. Other pathologies, such as a minute supernumerary tooth, desmoplastic ameloblastoma or extraosseous odontogenic cysts are located external to the upper or lower dentition, and might be derived from structures that transiently appear during early development of the oral vestibule in humans.

The microstructure and three-point bending behavior of Ni–Co/WC composite cladding coating

Abstract Ni–Co/WC composite coating was fabricated on ZG45 steel substrate through vacuum sintering cladding technology. Its microstructure, composition, and three-point bending behavior were analyzed through scanning electron microscopy, electron probe microanalysis, X-ray diffraction, and mechanical testing. Results show that the distribution of WC particles presents a 3D net-like shape. A metallurgical fusion area is observed at the interface between the composite coating and the substrate. The entire coating consists of a composite coating area, a transition area, and a diffusion fusion area. The main phases of the coating are WC, Cr7C3, Cr23C6, Ni3Si, FeNi3, and Ni–Co solid solution. Three-point bending results reveal that the softness coefficient of the whole sample when the composite coating was in a compressive stress state was larger than that when the composite coating was in a tensile stress state. The bending strength of the sample is 520 MPa when the composite coating is in a compressive stress state. This value is 66 % higher than that when the composite coating is located at the bottom. The cracks simultaneously extend to the substrate and interface when the composite coating was in a compressive stress state and to the substrate when the composite coating was in a tensile stress state. The fracture of the composite area is brittle, and the substrate fracture is ductile.

In Situ 3D Monitoring of Geometric Signatures in the Powder-Bed-Fusion Additive Manufacturing Process via Vision Sensing Methods.

Lack of monitoring of the in situ process signatures is one of the challenges that has been restricting the improvement of Powder-Bed-Fusion Additive Manufacturing (PBF AM). Among various process signatures, the monitoring of the geometric signatures is of high importance. This paper presents the use of vision sensing methods as a non-destructive in situ 3D measurement technique to monitor two main categories of geometric signatures: 3D surface topography and 3D contour data of the fusion area. To increase the efficiency and accuracy, an enhanced phase measuring profilometry (EPMP) is proposed to monitor the 3D surface topography of the powder bed and the fusion area reliably and rapidly. A slice model assisted contour detection method is developed to extract the contours of fusion area. The performance of the techniques is demonstrated with some selected measurements. Experimental results indicate that the proposed method can reveal irregularities caused by various defects and inspect the contour accuracy and surface quality. It holds the potential to be a powerful in situ 3D monitoring tool for manufacturing process optimization, close-loop control, and data visualization.

Endocardial‐mesenchymal transition underlies fusion of the conotruncal ridges during embryonic cardiac outflow tract septation

The embryonic cardiac outflow tract (conotruncus) is a single tubular chamber that connects the right ventricle with the aortic arch arteries. It contains two opposite, long and helical mesenchymal cushions covered by endocardial cells (conotruncal ridges). Conotruncal division (septation) gives rise to the adult right and left outflows together with the aortic and pulmonary valves. It takes place by fusion of the two opposite ridges and formation of the conotruncal septum. Although the participation of neural crest cells in septation is well established, the mechanism of fusion of the conotruncal ridges remains unknown. Defects in fusion have been shown to produce bicuspid aortic valve, the most prevalent human congenital cardiac malformation, in a hamster model.Three fusion mechanisms have been proposed to operate during embryonic development: epithelial adhesion, epithelial apoptosis and epithelial‐mesenchymal transition (EMT). The first mechanism entails the expression of adhesion molecules and the maintenance of the identity of cells in contact, whereas in the other two, epithelial cells covering the fusing structures disappear by apoptosis or by transforming into mesenchymal cells.The objective of this study is to elucidate the mechanism involved in the fusion of the conotruncal ridges. With this aim, ED 11–12 hamster embryos were used. Endocardial cell adhesion was assessed by immunofluorecence with VE‐CAD and CD34 antibodies. Apoptosis was detected by inmmunofluorescence for active caspase 3 and the TUNEL method. For EMT detection two methods were used: inmmunofluorescence colocalization of the above mentioned endocardial markers with the migration marker α‐actin, and mesenchymal localization of fluorescence after 12 hours ex vivo incubation of embryos with the membrane impermeable fluorescent molecule carboxifluorescein (CFSE).During septation, endocardial cells covering the surface of the conotruncal ridges were VE‐CAD+, CD34+, and α‐actin−, whereas those in the area of fusion, at the point of contact between opposite ridges were positive for the three markers. Distal to the area of fusion, only VE‐CAD−/CD34− mesenchymal cells were found, many of them positive for α‐actin. Apoptosis was detected in mesenchymal cells of the ridges, but not in endocardial cells. It was abundant during cushion remodeling at late stages, scarce during septation, and absent in the area of fusion. Embryos incubated with CFSE showed fluorescent endocardial cells as well as scattered fluorescent mesenchymal cells, usually positive for α‐actin, in the area of fusion closed to the endocardium.The results indicate that the mechanism of EMT, but not epithelial adhesion or apoptosis, is involved in the process of fusion of the conotruncal ridges. The EMT mechanism associated with conotruncal septation seems to be uncoupled from the process of formation of the endocardial cushions, which takes place at early stages. With these results, we can raise the hypothesis that defects in the EMT process may lead to different morphological types of bicuspid aortic valve.Support or Funding InformationThis study was supported by P10‐CTS‐6068 (Junta de Andalucía).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Wear-resistance Performance of Spray-welding Coating by Plasma Weld-surfacing

Alloy powders including Ni60, WC, Cr3C2, and TiC with different mass ratios were deposited on medium carbon low alloy steel by plasma welding. Through the experiments, the optimal alloy powder reinforcing cutter tool surface properties were discovered. The wear resistance properties were investigated on the impact abrasive wear tester. The experimental results show that in terms of microstructure, there exists the shape of herringbone, spider mesh, broken flower structures in coatings. In addition, fusion area of four specimens surfacing welding layer displays a large number of acicular martensite with a small amount of austenite. The coating mainly consists of Ni-Cr-Fe austenitic phase and the other precipitates. TiC density is smaller, its content is less in alloy powder, in the process of surfacing welding, TiC is melted fully, which is mainly distributed in surface layer and middle layer of hard facing layer. The content of TiC gradually reduces from surface layer of hard facing layer to the fusion area. Compared to TiC, the density of tungsten carbide and chromium carbide is larger, there exist tungsten carbide and chromium carbide particles, which are not completely melted near the fusion area. The micro-hardness presents gradient change from the fusion area to the surface layer of hard facing layer, and the hardness of the middle layer is slightly lower than that of the fusion area, and the hardness increases near the surface layer.

The role of powder layer thickness on the quality of SLM printed parts

Achieving good mechanical properties as well as the dimensional accuracy and the smooth surface quality of selective laser melting printed parts with minimal post treatments are essential in additive manufacturing. In the present study, Inconel 718 samples with different powder layer thickness (20, 30, 40 and 50μm) were additively fabricated using 3D Systems ProX-300 machine. The results reveal that the lower the layer thickness, the denser and good dimensional accuracy were achieved. Marginally higher mechanical properties and microhardness were also obtained at the lower thickness while the failure strain was still high. This can be explained through significant change in the microstructure due to different cooling rate and thermal cycles. In addition, the formation of ɤ′ and ɤ″ intermetallic phases, which were well distributed in the matrix and grain boundaries, during heating/cooling, gave rise in the strengths. Fractography shows the plastic deformation band due to work hardening and the crack initiation sites at sub-micro/micro pores, lack of fusion areas and the boundary of unmelted particles. The study would guide engineers balance their options between the production rate and the building parts’ quality.

Surgical Outcomes of Posterior Spinal Fusion Alone Using Cervical Pedicle Screw Constructs for Cervical Disorders Associated With Athetoid Cerebral Palsy.

Retrospective case series. The aim of this study was to investigate clinical outcomes after posterior spinal fusion (PSF) using cervical pedicle screw (CPS) constructs for cervical disorders associated with athetoid cerebral palsy (CP). Traditionally, most patients with cervical myelopathy associated with CP have required combined anterior and posterior fusion to achieve solid stability against severe involuntary movement. Thirty-one CP patients with cervical disorders who underwent PSF alone with a minimum 2-year follow-up (mean 58 months) were analyzed. All patients were treated with PSF using CPS constructs with or without decompression procedures. The average number of fused segments was 5.1 (range, 1-10 segments), and a halo jacket was applied in 16 patients for at least 2 months after surgery. Clinical outcomes using the Japanese Orthoedic Association scoring system (JOA score) and walking ability, radiographic sagittal alignment, fusion status, and surgery-related complications were evaluated. The JOA score improved from 8.3 points preoperatively to 10.9 points at the final follow-up (P < 0.05). Although no patients experienced deterioration in their walking ability postoperatively, 10 patients were unable to walk at the final follow-up. Sagittal alignment, including C0-2 angle, C2-7 angle, and local alignment in fused segments, was maintained postoperatively. Twenty-five patients achieved fusion at the final follow-up (fusion rate: 81%), and fivepatients with nonunion required additional surgery. With regard to complications, 5 patients encountered postoperative upper extremity palsy. The CPS construct is amenable to achieve a relatively high fusion rate without correction loss, and good clinical outcomes can be achieved with a posterior single approach for CP patients. In the future, efforts should be made to make appropriate decisions regarding the fusion area, take preventative measures against postoperative upper extremity palsy, and simplify external orthoses after surgery, especially with the use of a halo jacket. 4.

A New Multimodal Approach for Password Strength Estimation—Part I: Theory and Algorithms

After more than two decades of research in the field of password strength estimation, one clear conclusion may be drawn: no password strength metric by itself is better than all other metrics for every possible password. Building upon this certainty and also taking advantage of the knowledge gained in the area of information fusion, in this paper, we propose a novel multimodal strength metric that combines several imperfect individual metrics to benefit from their strong points in order to overcome many of their weaknesses. The final multimodal metric comprises different modules based both on heuristics and statistics, which, after their fusion, succeed to provide in real time a realistic and reliable feedback regarding the “guessability” of passwords. The validation protocol and the test results are presented and discussed in a companion paper.

0044 - Determination of Fusion Level in Scoliosis Surgery—Is It an Art or Science?

BACKGROUND & AIM: Decision to choose the level of fusion in adolescent idiopathic scoliosis (AIS) have always been a challenge. Adequate fusion levels need to be achieved to obtain coronal and sagittal balance and include minimum number of segments in fusion. Supine side bending radiographs have been used in the pre-operative evaluation of idiopathic scoliosis to determine curve flexibility and fusion area. However final decision on level of fusion is made intraoperatively. In this study, the aim was to determine if the surgeon's decision to choose levels of fusion based on PA and bending radiographs accurately predicted intra-operative decision.

Titanium Alloys Thin Sheet Welding with the Use of Concentrated Solar Energy

The present study deals with the welding of titanium alloys thin sheets 1.3 mm thick, with the use of concentrated solar energy. The experimental part of the work took place at a medium size solar furnace at the installation of the Centre National de la Recherche Scientifique, at Odeillo, in Southern France, where similar and dissimilar defect-free welds of titanium Grades 4 and 6 were achieved, in the butt joint configuration. After the determination of the appropriate welding conditions, the optimum welded structures were examined and characterized microstructurally, by means of light optical microscopy, scanning electron microscopy, and microhardness testing. In addition, test pieces extracted from the weldments were tested under uniaxial tensile loading aiming to the estimation of the strength and the ductility of the joint. The analysis of the experimental results and the recorded data led to the basic concluding remarks which demonstrate increased hardness distribution inside the fusion area and severe loss of ductility, but adequate yield and tensile strength of the welds.

Osteogenic Potential of Tauroursodeoxycholic Acid as an Alternative to rhBMP-2 in a Mouse Spinal Fusion Model.

The non-union rate after lumbar spinal fusion is potentially as high as 48%. To support efficient bone regeneration, recombinant human bone morphogenetic protein-2 (rhBMP-2) is commonly used as it is regarded as the most potent bone-inducing molecule. However, recently, there have been increasing concerns on the use of rhBMP-2 such as serious complications, including seroma and heterotopic ossification, and the low quality of bone at the center of fusion mass. Thus, many studies were conducted to find and to develop a potential alternative to rhBMP-2. In this study, we investigated the osteogenic potential of tauroursodeoxycholic acid (TUDCA) in the mouse fusion model and compared its effects with rhBMP-2. Twenty-four mice underwent bilateral posterolateral lumbar spinal fusion bone formation at L4-L5. Collagen sponge infused with saline, TUDCA, or rhBMP-2 was implanted at the fusion area. Two and 4 weeks postimplantation, bone formation and tissue regeneration were evaluated via micro-computed tomography and histological analysis. Compared with the TUDCA-treated group, the rhBMP-2 treatment produced a higher amount of bone fusion formation after 2 weeks but also showed higher resorption of the centralized bone after 4 weeks. Interestingly, the TUDCA-treated group developed higher trabecular thickness compared with rhBMP-2 after 4 weeks. Moreover, TUDCA treatment showed distinct angiogenic activity in human umbilical vein endothelial cells as confirmed by an in vitro tube formation assay. Our findings suggest that TUDCA is comparable to rhBMP-2 in supporting bone regeneration and spinal bone formation fusion by increasing trabecular thickness and promoting angiogenesis. Finally, our results indicate that TUDCA can be utilized as a potential alternative to rhBMP-2.

Failure Patterns in Standalone Anterior Cervical Discectomy and Fusion Implants.

Anterior cervical discectomy and fusion is commonly performed using an allograft or autograft implant and anterior screw-supported plate. There has been an increase in the use of standalone cage devices due to ease of use and studies suggesting a lower rate of acute postoperative dysphagia. We review our experience with standalone cage devices and identify risk factors, patterns of failure, and revision surgery approaches. We performed a retrospective case series of patients treated at a single tertiary care institution between March 2014 and March 2015. Inclusion criteria were aged 18-100 years, 1- or 2-level anterior cervical discectomy and fusion with a standalone cervical cage. Data collected included demographics, comorbidities, Charlson comorbidity score, primary diagnosis, and surgical characteristics. Descriptive statistics were performed for risk of readmission, implant failure, revision, and other complications. We identified 211 patients who met our study criteria. Average surgical time was 107 ± 43 minutes, with an estimated blood loss of 84.6 ± 32.4 mL. There were 11 (5.2%) readmissions. There were 10 (4.74%) implant failures (5 involving single-level surgery and 5 involving 2-level surgery), with 7 cases of pseudoarthrosis. Mechanisms of failure included a C5 body fracture, fusion in a kyphotic alignment after graft subsidence, and acute spondylolisthesis. Revision surgery after standalone anterior cervical implants can be complex. Posterior cervical fusion remains a valuable approach to avoid possible vertebral body fracture and loss of fusion area associated with the removal of implants secured through the endplates of adjacent vertebral bodies.

Measurement of spatial refractive index distributions of fusion spliced optical fibers by digital holographic microtomography

Digital holographic microtomography is improved and applied to the measurements of three-dimensional refractive index distributions of fusion spliced optical fibers. Tomographic images are reconstructed from full-angle phase projection images obtained with a setup-rotation approach, in which the laser source, the optical system and the image sensor are arranged on an optical breadboard and synchronously rotated around the fixed object. For retrieving high-quality tomographic images, a numerical method is proposed to compensate the unwanted movements of the object in the lateral, axial and vertical directions during rotation. The compensation is implemented on the two-dimensional phase images instead of the sinogram. The experimental results exhibit distinctly the internal structures of fusion splices between a single-mode fiber and other fibers, including a multi-mode fiber, a panda polarization maintaining fiber, a bow-tie polarization maintaining fiber and a photonic crystal fiber. In particular, the internal structure distortion in the fusion areas can be intuitively observed, such as the expansion of the stress zones of polarization maintaining fibers, the collapse of the air holes of photonic crystal fibers, etc.

Effect of welding parameters on properties of HDPE geomembrane seams

The effect of various welding parameters of a dual-wedge welding technique on the physical, mechanical and chemical properties of high-density polyethylene (HDPE) geomembrane seam specimens is examined. These seams were welded with sufficient heat, insufficient heat and excessive heat at specific speeds and nip pressures. The thickness of the fusion area and the width of the air channel provided an acceptable indication of the quality of the welding. Investigation of the seam specimens' mechanical properties showed that physical ageing had occurred. The impact of welding on antioxidants was evaluated using the standard oxidative induction time (Std-OIT) test method. The Std-OIT results showed that the outer edge of squeeze-out was greatly affected by the thermal welding. Scanning electron microscopy analysis confirmed that the morphology of the outer edge of squeeze-out was altered after welding. However, the Std-OIT test on other locations of the seam specimens indicated that welding had an insignificant impact on the Std-OIT values for the particular geomembrane and welding parameters considered.

Shielding gas effects on double-sided synchronous autogenous GTA weldability of high nitrogen austenitic stainless steel

Acceptable weld formation in high nitrogen austenitic stainless steel (HNASS) was achieved when nitrogen gas (N2) was added to the Ar-based shielding gas. Although a relatively unstable process, in double-sided synchronous autogenous gas tungsten arc (GTA) welding (DSSAGW), added N2 enabled the arc plasma to shrink and accordingly heightened the arc voltage, leading to increased fusion areas of welds. Added N2 in the shielding gas was very beneficial for suppressing nitrogen loss in welded joints, with the nitrogen content in the weld zone (WZ) increased to 1.25% with pure N2 shielding gas, while the δ-ferrite content slightly decreased. With increased N2 in shielding gas, both the primary and secondary dendrite arm spacing in the WZ increased, while the equiaxed austenite in heat-affected zone (HAZ) varied rather little. The WZ microhardness increased with N2 addition to the shielding gas, indicating nitrogen’s strong solid solution strengthening effects. Based on these results, N2 was considered to be a promising shielding gas for HNASS welding in DSSAGW and the optimal N2 and Ar proportions judged to be below 2/8 (by vol.).

Comparison of Remote Sensing Image Fusion Strategies Adopted in HSV and IHS

It has been always a challenging task to keep an ideal balance of spectral and spatial resolution for merging panchromatic image and multispectral image. The mathematical theories such as color space transformation and Wavelet Packet Analysis are usually employed in information fusion area. Combining color space conversion with wavelet packet theory is a way of researching remote sensing image fusion algorithms further. In the paper, there are three existing image fusion strategies applied to the second layer of frequency bands decomposed by wavelet packet analysis in the HSV and the IHS (triangular coordinate) color space, respectively. Serial experiments demonstrate two core concepts. One is the effects of image fusion strategies based on region is super to those of fusion strategy based on pixel for the same color space; the other is the different performances are measured in the two color spaces. Specially, the space definition for image fused in the former color space is inferior to that in the latter color space; while the spectrum content for image fused in the former color space retains better than in the latter color space, when using the same fusion strategy in the two color space. As a result, application containing HSV space conversion can alleviate spectral deterioration, whereas fusion operation of IHS transformation can lift spatial definition.

Radiological assessment of experimental mono-segmental posterior-lateral lumbar fusion using autologous platelet rich fibrin

The results of the use of autologous platelet-rich fibrin, for pos­terolateral lumbar spinal fusion are discussed. Objective: to evaluate the radiographic signs of experimental posterolateral lumbar spine fusion using fibrin-rich platelets. Methods: mono segmental posterolateral lumbar spinal fusion performed in 42 adult male California rabbits aged 4–5 months, which were divided into 6 groups of 7 animals each. In the control group 1 grafts were not used in group 2 used the local autograft, group 3 — local autograft combined with fibrin-rich platelets, 4 — al­lograft of ilium, 5 — allograft from ilium combined with fibrin-rich platelets, 6 — fibrin-rich platelets. Results: revealed ra­diographic characteristics of posterolateral osteoplastic fusion, namely the formation of continuous trabecular bone in the area of spinal fusion, preserved height of interbody gaps, homoge­nous structure of newly formed bone, increasing the intensity of X-ray images in fusion masses. In radiometric studies iden­tified more intensive bone density block of rabbits in groups 3 and 5, as well as forming a homogeneous bone accretion in group 6. Conclusions: groups of rabbits with osteoplastic spinal fusion detected radiographic signs of bone formed block in 77.1 % of cases in the control decortication group of trans­verse processes — in 57.1 %. Results of roentgenometric zone fusion evaluation suggest that autologous platelet rich fibrin, promotes strong bone accretion.

Foundations for improved integration – Using Systems Engineering in Programme and Project Management

AbstractThe INCOSE UK/APM Joint Working Group (JWG) on Systems Engineering (SE) and Project/Programme Management (PM) Integration has been addressing the shared understanding of the two disciplines and how they work together. It seeks to promote the benefits of systems thinking across the wider decision‐making community, and to understand how to deliver these benefits.As part of its work, the JWG has compared and categorized life cycles and processes within the two disciplines; analysed subsequent theoretical touch points, overlaps and fusion areas; identified examples of actual large projects with integrated SE and PM approaches; and used all this information to generate a set of underlying Principles for improved integration. In addition, the JWG has identified a set of Top Tips to help establish the Principles.This information forms part of the expanding body of knowledge being developed by the JWG and helping to lay the foundation for improved integration.

Proximal junctional kyphosis in adult spinal deformity with long spinal fusion from T9/T10 to the ilium.

Proximal junctional kyphosis (PJK) is a common complication after corrective long spinal fusion for adult spinal deformity. Although some reports evaluated PJK after corrective long spinal fusion, there is no report about analysis of PJK cases in the same fusion area. The purpose of this study to investigated the incidence of and risk factors for PJK in adults undergoing long spinal fusion from the distal thoracic vertebrae (T9/T10) to the ilium. We enrolled 56 adult patients (>40 years of age) who underwent posterior corrective surgery with same fusion area from T9 or T10 to the ilium for spinal deformity. Pre- and postoperative radiographic measurements included the sagittal vertical axis (SVA), lumbar lordosis (LL), thoracic kyphosis (TK), pelvic tilt (PT), and pelvic incidence minus LL (PI-LL). The Oswestry disability index (ODI) was used to evaluate patient outcomes preoperatively and one year after surgery. We analyzed the incidence for PJK and compared PJK and non-PJK cases. PJK at the final follow-up occurred in 19 of 56 (33.9%) patients. The mean age and ODI were not significantly different between the PJK and non-PJK groups. Both two groups had good spinopelvic sagittal alignment after surgery in terms of SVA and PI-LL. Only three cases required revision surgery for symptomatic PJK. Three cases had history of rheumatoid arthritis and/or total hip arthroplasty surgery. The incidence of PJK was 33.9%, and ODI was not significantly different between the PJK and non-PJK groups. Symptomatic PJK was only three cases and all of them had lower extremity joint disorders. We should pay attention also lower extremity joint to prevent symptomatic PJK at the lower thoracic level.