Keun Su Kim

Yonsei University Hospital, Sŏul, Seoul, South Korea

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Publications (60)168.39 Total impact

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    ABSTRACT: Minimally invasive surgery with a transforaminal lumbar interbody fusion (MIS TLIF) is an important minimally invasive fusion technique for the lumbar spine. Lumbar spine reoperation is challenging and is thought to have greater complication risks. The purpose of this study was to compare MIS TLIF with unilateral screw fixation perioperative results between primary and revision surgeries. This was a prospective study that included 46 patients who underwent MIS TLIF with unilateral pedicle screw. The patients were divided into two groups, primary and revision MIS TLIF, to compare perioperative results and complications. The two groups were similar in age, sex, and level of operation, and were not significantly different in the length of follow-up or clinical results. Although dural tears were more common with the revision group (primary 1; revision 4), operation time, blood loss, total perioperative complication, and fusion rates were not significantly different between the two groups. Both groups showed substantial improvements in VAS and ODI scores one year after surgical treatment. Revision MIS TLIF performed by an experienced surgeon does not necessarily increase the risk of perioperative complication compared with primary surgery. MIS TLIF with unilateral pedicle screw fixation is a valuable option for revision lumbar surgery.
    BioMed Research International 01/2014; 2014:919248. · 2.88 Impact Factor
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    ABSTRACT: Surgeon spine angle during surgery was studied ergonomically and the kinematics of the surgeon's spine was related with musculoskeletal fatigue and pain. Spine angles varied depending on operation table height and visualization method, and in a previous paper we showed that the use of a loupe and a table height at the midpoint between the umbilicus and the sternum are optimal for reducing musculoskeletal loading. However, no studies have previously included a microscope as a possible visualization method. The objective of this study is to assess differences in surgeon spine angles depending on operating table height and visualization method, including microscope. We enrolled 18 experienced spine surgeons for this study, who each performed a discectomy using a spine surgery simulator. Three different methods were used to visualize the surgical field (naked eye, loupe, microscope) and three different operating table heights (anterior superior iliac spine, umbilicus, the midpoint between the umbilicus and the sternum) were studied. Whole spine angles were compared for three different views during the discectomy simulation: midline, ipsilateral, and contralateral. A 16-camera optoelectronic motion analysis system was used, and 16 markers were placed from the head to the pelvis. Lumbar lordosis, thoracic kyphosis, cervical lordosis, and occipital angle were compared between the different operating table heights and visualization methods as well as a natural standing position. Whole spine angles differed significantly depending on visualization method. All parameters were closer to natural standing values when discectomy was performed with a microscope, and there were no differences between the naked eye and the loupe. Whole spine angles were also found to differ from the natural standing position depending on operating table height, and became closer to natural standing position values as the operating table height increased, independent of the visualization method. When using a microscope, lumbar lordosis, thoracic kyphosis, and cervical lordosis showed no differences according to table heights above the umbilicus. This study suggests that the use of a microscope and a table height above the umbilicus are optimal for reducing surgeon musculoskeletal fatigue.
    European Spine Journal 12/2013; · 2.47 Impact Factor
  • Keun Su Kim, Dong Hwa Heo
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    ABSTRACT: Prospective clinical study. To evaluate the factors that would predispose a patient to HO formation after cervical arthroplasty. Heterotopic ossification (HO) after arthroplasty is one of the complications of cervical total disc replacement (TDR). However, the predisposing factors and pathophysiology of HO have not been precisely described. We prospectively enrolled and followed 23 patients, who received single-level arthroplasty with ProDisc-C, for 5 years after the operation. The patients who developed grade 3 or 4 HO were classified into the "high-grade HO group," whereas the patients grade 0, 1, or 2 HO were classified into the "low-grade HO group." We compared the postoperative changes in the range of motion (ROM) and height of the functional segmental unit (FSU) of the implantation segments between the 2 groups. The mean differences in height and ROM of the FSU were 2.59±1.42 mm and 6.7±3.2° in the high-grade HO group, and.87 ±0.72 mm and 3.1±2.8° in the low-grade HO group. The mean differences in height and ROM of the FSU were significantly higher in the high-grade HO group than in the low-grade HO group (P<0.05, Table 2). After cervical arthroplasty, the height of the FSU and ROM of the implantation segments were significantly increased in the high-grade HO group compared to the low-grade HO group. Over-correction of the height of the FSU and increase in the ROM of the implantation segment may influence the formation of HOs after cervical arthroplasty.
    Journal of spinal disorders & techniques 11/2013; · 1.21 Impact Factor
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    ABSTRACT: Purpose: All structures of the spine, including the spinal canal, change continuously with age. The purpose of this study was to determine how the spinal canal of the lumbar spine changes with age. The L4/5 is the most common site of spinal stenosis and has the largest flexion-extension motion, whereas the T5/6 has the least motion. Therefore, we measured the spinal canal diameter and vertebral body height at T5, T6, L4, and L5 with age. Materials and Methods: This was a retrospective study of aged 40 to 77 years. We reviewed whole spine sagittal MRIs of 370 patients with lumbar spinal stenosis (LSS) (Group 2) and 166 herniated cervical disc (HCD) (Group 1). Each group was divided into four age groups, and demographic parameters (age, gender, height, weight, BMI), the mid-spinal canal diameter, and mid-vertebrae height at T5, T6, L4, L5 were compared. Within- and between-group comparisons were made to evaluate changes by age and correlations were carried out to evaluate the relationships between all parameters. Results: Height, weight, and all radiologic parameters were significantly lower in Group 2 than Group 1. Group 1 did not show any differences, when based on age, but in Group 2, height, weight, and T6, L4, and L5 height were significantly decreased in patients in their 70's than patients in their 40's, except for spinal canal diameter. Age was associated with all parameters except spinal canal diameter. Conclusion: Vertebral height decreased with age, but spinal canal diameter did not change in patients with either LSS or HCD. Mid-spinal canal diameter was not affected by aging.
    Yonsei medical journal 11/2013; 54(6):1498-504. · 0.77 Impact Factor
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    ABSTRACT: Object Clinical results for unilateral pedicle screw fixation after lumbar interbody fusion have been reported to be as good as those for bilateral instrumentation. However, no studies have directly compared unilateral and bilateral percutaneous pedicle screw fixation after minimally invasive surgery (MIS) for transforaminal lumbar interbody fusion (TLIF). The purpose of this study was to determine whether unilateral percutaneous pedicle screw fixation is comparable with bilateral percutaneous pedicle screw fixation in 1-segment MIS TLIF. Methods This was a prospective randomized study of 53 patients who underwent unilateral or bilateral percutaneous pedicle screw fixation after MIS TLIF for 1-segment lumbar degenerative disc disease. Twenty-six patients were assigned to a unilateral percutaneous pedicle screw fixation group and 27 patients were assigned to a bilateral percutaneous pedicle screw fixation group. Operative time, blood loss, clinical outcomes (that is, Oswestry Disability Index [ODI] and visual analog scale [VAS] scores), complication rates, and fusion rates were assessed using CT scanning 2 years after surgical treatment. Results The 2 groups were similar in age, sex, preoperative diagnosis, and operated level, and they did not differ significantly in the length of follow-up (27.5 [Group 1] vs 28.9 [Group 2] months) or clinical results. Both groups showed substantial improvements in VAS and ODI scores 2 years after surgical treatment. The groups differed significantly in operative time (unilateral 84.2 minutes; bilateral 137.6 minutes), blood loss (unilateral 92.7 ml; bilateral, 232.0 ml), fusion rate (unilateral 84.6%; bilateral 96.3%), and postoperative scoliotic change (unilateral 23.1%; bilateral 3.7%). Conclusions Unilateral and bilateral screw fixation after MIS TLIF produced similar clinical results. Although perioperative results were better with unilateral screw fixation, the long-term results were better with bilateral screw fixation, suggesting bilateral screw fixation is a better choice after MIS TLIF.
    Neurosurgical FOCUS 08/2013; 35(2):E11. · 2.49 Impact Factor
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    ABSTRACT: Charge carriers in bilayer graphene are widely believed to be massive Dirac fermions that have a bandgap tunable by a transverse electric field. However, a full transport gap, despite its importance for device applications, has not been clearly observed in gated bilayer graphene, a long-standing puzzle. Moreover, the low-energy electronic structure of bilayer graphene is widely held to be unstable towards symmetry breaking either by structural distortions, such as twist, strain, or electronic interactions that can lead to various ground states. Which effect dominates the physics at low energies is hotly debated. Here we show both by direct band-structure measurements and by calculations that a native imperfection of bilayer graphene, a distribution of twists whose size is as small as ~0.1°, is sufficient to generate a completely new electronic spectrum consisting of massive and massless Dirac fermions. The massless spectrum is robust against strong electric fields, and has a unusual topology in momentum space consisting of closed arcs having an exotic chiral pseudospin texture, which can be tuned by varying the charge density. The discovery of this unusual Dirac spectrum not only complements the framework of massive Dirac fermions, widely relevant to charge transport in bilayer graphene, but also supports the possibility of valley Hall transport.
    Nature Material 07/2013; · 35.75 Impact Factor
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    ABSTRACT: BACKGROUND CONTEXT: Heterotopic ossification (HO) is defined as a formation of bone outside the skeletal system. The reported HO occurrence rate in cervical artificial disc replacement (ADR) is unexpectedly high and is known to vary. However, the predisposing factors for HO in cervical ADR have not yet been elucidated. PURPOSE: Investigation of the predisposing factors of HO in cervical arthroplasty and the relationship between degeneration of the cervical spine and HO occurrence. STUDY DESIGN: Retrospective study to discover predisposing factors of HO in cervical arthroplasty. PATIENT SAMPLE: A total of 170 patients who underwent cervical ADR were enrolled including full follow-up clinical and radiologic data. OUTCOME MEASURES: Radiologic outcomes were assessed by identification of HOs according to McAfee's classifications. METHODS: This study enrolled a total of 170 patients who underwent cervical ADR. Pre-existing degenerative change included anterior or posterior osteophytes, ossification of the anterior longitudinal ligament, posterior longitudinal ligament, or ligamentum nuchae. The relationships between basic patient data, pre-existing degenerative change, and HO were investigated using linear logistic regression analysis. RESULTS: Among all 170 patients, HO was found in 69 patients (40.6%). Among the postulated predisposing factors, only male gender and artificial disc device type were shown to be statistically significant. Unexpectedly, preoperative degenerative changes in the cervical spine exerted no significant influence on the occurrence of HOs. The odds ratio of male gender compared with female gender was 2.117. With regard to device type, the odds ratios of Mobi-C (LDR medical, Troyes, France) and ProDisc-C (Synthes, Inc., West Chester, PA, USA) were 5.262 and 7.449, respectively, compared with the Bryan disc. CONCLUSIONS: Definite differences in occurrence rate according to the gender of patients and the prosthesis type were identified in this study. Moreover, factors indefinably expected to influence HO in the past were not shown to be risk factors thereof, the results of which may be meaningful to future studies.
    The spine journal: official journal of the North American Spine Society 03/2013; · 2.90 Impact Factor
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    DPG-Physik > DPG-Verhandlungen > 2013 > Regensburg; 03/2013
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    ABSTRACT: The most widely accepted theoretical model to describe charge carriers in bilayer graphene is ``massive Dirac fermions'', characterized by a nearly parabolic band pair touching each other at the Dirac energy. This electronic structure of bilayer graphene is widely believed to be unstable towards symmetry breaking either by structural distortions, such as twist and strain, or electronic interactions. In this work, we investigate quasi-freestanding bilayer graphene by angle-resolved photoemission spectroscopy, which shows an unexpected electronic spectrum, consisting of both massive and massless Dirac fermions. The latter has a unique band topology with a chiral pseudospin texture, and its origin will be discussed in terms of symmetry breaking induced by a native imperfection of bilayer graphene.
    03/2013;
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    ABSTRACT: The titanium oxide TiO2 has been object of extensive studies because of its suitability in many practical fields, ranging from photovoltaic applications, to catalysis, memristors, and others. As for many other transition metal oxides, great attention has been devoted to the impact on the electronic structure of different doping mechanisms, either extrinsic or due to the creation of oxygen vacancies. Here we report an angle-resolved photoemission (ARPES) work on TiO2 single crystals and epitaxial films grown wIth the in situ pulsed-laser-deposition (PLD) system available on beamline 7.0.1 at the Advanced Light Source. We show the evolution of the electronic structure as a function of the amount of oxygen vacancies induced by the photon beam.
    03/2013;
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    ABSTRACT: We investigate the atomic-scale tunneling characteristics of bilayer graphene on silicon carbide using the scanning tunneling microscopy. The high-resolution tunneling spectroscopy reveals an unexpected negative differential resistance (NDR) at the Dirac energy, which spatially varies within the single unit cell of bilayer graphene. The origin of NDR is explained by two near-gap van Hove singularities emerging in the electronic spectrum of bilayer graphene under a transverse electric field, which are strongly localized on two sublattices in different layers. Furthermore, defects near the tunneling contact are found to strongly impact on NDR through the electron interference. Our result provides an atomic-level understanding of quantum tunneling in bilayer graphene, and constitutes a useful step towards graphene-based tunneling devices.
    Physical Review Letters 01/2013; 110(3):036804. · 7.73 Impact Factor
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    ABSTRACT: PURPOSE: It is well known that arthrodesis is associated with adjacent segment degeneration (ASD). However, previous studies were performed with simple radiography or CT. MRI is most sensitive in assessing the degenerative change of a disc, and this is the first study about ASD by radiography, CT and MRI. We sought to factors related to ASD at cervical spine by an MRI and CT, after anterior cervical spine surgery. MATERIALS AND METHODS: This is a retrospective cross-sectional study of cervical disc herniation. Patients of cervical disc herniation with only radiculopathy were treated with either arthroplasty (22 patients) or ACDF with cage alone (21 patients). These patients were required to undergo MRI, CT and radiography preoperatively, as well as radiography follow-up for 3 months and 1 year, and we conducted a cross-sectional study by MRI, CT and radiography including clinical evaluations 5 years after. Clinical outcomes were assessed using VAS and NDI. The fusion rate and ASD rate, and radiologic parameters (cervical lordosis, operated segmental height, C2-7 ROM, operated segmental ROM, upper segmental ROM and lower segmental ROM) were measured. RESULTS: The study groups were demographically similar, and substantial improvements in VAS (for arm) and NDI (for neck) scores were noted, and there were no significant differences between groups. Fusion rates were 95.2 % in the fusion group and 4.5 % in the arthroplasty group. ASD rates of the fusion and arthroplasty groups were 42.9 and 50 %, respectively. Among the radiologic parameters, operated segmental height and operated segmental ROM significantly decreased, while the upper segmental ROM significantly increased in the fusion group. In a comparative study between patients with ASD and without ASD, the clinical results were found to be similar, although preexisting ASD and other segment degeneration were significantly higher in the ASD group. C2-7 ROM was significantly decreased in ASD group, and other radiologic parameters have no significant differences between groups. CONCLUSION: The ASD rate of 46.5 % after ACDF or arthroplasty, and arthroplasty did not significantly lower the rate of ASD. ASD occurred in patients who had preexisting ASD and in patients who also had other segment degeneration. ASD may be associated with a natural history of cervical spondylosis rather than arthrodesis.
    European Spine Journal 12/2012; · 2.47 Impact Factor
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    ABSTRACT: Interest in the use of graphene in electronic devices has motivated an explosion in the study of this remarkable material. The simple, linear Dirac cone band structure offers a unique possibility to investigate its finer details by angle-resolved photoelectron spectroscopy (ARPES). Indeed, ARPES has been performed on graphene grown on metal substrates but electronic applications require an insulating substrate. Epitaxial graphene grown by the thermal decomposition of silicon carbide (SiC) is an ideal candidate for this due to the large scale, uniform graphene layers produced. The experimental spectral function of epitaxial graphene on SiC has been extensively studied. However, until now the cause of an anisotropy in the spectral width of the Fermi surface has not been determined. In the current work we show, by comparison of the spectral function to a semi-empirical model, that the anisotropy is due to small scale rotational disorder ($\sim\pm$ 0.15$^{\circ}$) of graphene domains in graphene grown on SiC(0001) samples. In addition to the direct benefit in the understanding of graphene's electronic structure this work suggests a mechanism to explain similar variations in related ARPES data.
    New Journal of Physics 09/2012; 15(2). · 4.06 Impact Factor
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    ABSTRACT: The ventriculus terminalis (VT) in adults is a rare pathology. We report various MR imaging features of the adult VT. Ten patients were included in this retrospective review.. All patients had undergone magnetic resonance (MR imaging with a surface coil that used two different 1.5T MR systems. All patients had undergone initial and follow-up MR imaging with contrast enhancement using gadopentate dimeglumine. Three patients underwent additional MR imaging using the echocardiogram-gated spatial modulation of magnetization (SPAMM) technique. If a shift in tagging band during the systolic phase was less than half of the band space, it was defined as a "non-pulsatile fluid". Two neuroradiologists independently reviewed these images, while clinical symptoms and outcomes were statistically analyzed between the treated and non-treated group. All cases presented an intramedullary cystic lesion in the conus medullaris and showed the same signal intensity as CSF. Three VTs had intracystic septation and cord edema, which were pathologically confirmed after surgery; two of these were associated with kyphotic deformity and spinal arteriovenous malformation. SPAMM-MRI of 3 patients demonstrated non-pulsatile fluid motion within the VT. In the treated group, clinical symptoms improved better than the non-treated group. The adult VT shows some unusual imaging features, including septation, cord edema, and coexistence of a spinal AVM, as well as the typical findings. Surgical maneuvers may be considered as a treatment option in adult VT with progressive neurological symptoms.
    Korean journal of radiology: official journal of the Korean Radiological Society 09/2012; 13(5):557-63. · 1.32 Impact Factor
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    ABSTRACT: PURPOSE: The ergonomic problems for surgeons during spine surgery are an awkward body posture, repetitive movements, increased muscle activity, an overflexed spine, and a protracted time in a standing posture. The authors analyzed whole spine angles during discectomy. The objective of this study is to assess differences in surgeon whole spines angles according to operating table height and the methods used to visualize surgical field. MATERIALS AND METHODS: A cohort of 12 experienced spine surgeons was enrolled. Twelve experienced spine surgeons performed discectomy using a spine surgery simulator. Three different methods were used to visualize the surgical field (naked eye, loupe, and out of loupe) and three different operating table heights. Whole spine angles were compared for three different views during discectomy simulation; midline, ipsilateral, and contralateral. A 16-camera optoelectronic motion analysis system was used, and 16 markers were placed from head to pelvis. Lumbar lordosis, thoracic kyphosis, cervical lordosis, and occipital angle were compared at the different operating table heights, while using the three visualization methods, with natural standing position. RESULTS: Whole spine angles were significantly different for visualization methods. Lumbar lordosis, cervical lordosis, and occipital angle were closer to natural standing values when discectomy was performed with a loupe, but most measures differed from natural standing values when performed out of loupe. Thoracic kyphosis was also similar to the natural standing position during discectomy using a loupe, but differed from the natural standing position when performed with naked eye. Whole spine angles were also found to differ from the natural standing position according to operating table height, and became closer to natural standing position values as operating table height increased, when simulation was conducted with loupe. CONCLUSION: This study suggests that loupe use and a table height midpoint between the umbilicus and sternum are optimal for reducing surgeon musculoskeletal fatigue.
    European Spine Journal 07/2012; · 2.47 Impact Factor
  • Keun Su Kim, Han Woong Yeom
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    ABSTRACT: The electronic band structure of a liquid metal was investigated by measuring precisely the evolution of angle-resolved photoelectron spectra during the melting of a Pb monolayer self-assembled on a Si(111) surface. We found that the liquid Pb monolayer exhibits a free-electron-like band and it undergoes a coherent radial scattering, imposed by the radial correlation of constituent atoms, to form a characteristic secondary hole band. This unique double-radial bands and their gradual evolution during melting can be reproduced, including detailed spectral intensity profiles, with our radial scattering model based on a theoretical prediction of 1962. This result provides a missing link to relate atomic and electronic structures of liquid metals, which can be generally applied to strongly disordered states of matter.
    02/2012;
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    Keun Su Kim, Han Woong Yeom
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    ABSTRACT: The electronic band structure of a liquid metal was investigated by measuring precisely the evolution of angle-resolved photoelectron spectra during the melting of a Pb monolayer on a Si(111) surface. We found that the liquid monolayer exhibits a free-electron-like band and it undergoes a coherent radial scattering, imposed by the radial correlation of constituent atoms, to form a characteristic secondary hole band. These unique double-radial bands and their gradual evolution during melting can be quantitatively reproduced, including detailed spectral intensity profiles, with our radial scattering model based on a theoretical prediction of 1962. Our result establishes the radial band structure as a key concept for describing the nature of electrons in strongly disordered states of matter.
    Physical Review Letters 09/2011; 107(13):136402. · 7.73 Impact Factor
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    ABSTRACT: The electronic structure of graphene on Cu(111) and Cu(100) single crystals is investigated using low energy electron microscopy, low energy electron diffraction and angle resolved photoemission spectroscopy. On both substrates the graphene is rotationally disordered and interactions between the graphene and substrate lead to a shift in the Dirac crossing of $\sim$ -0.3 eV and the opening of a $\sim$ 250 meV gap. Exposure of the samples to air resulted in intercalation of oxygen under the graphene on Cu(100), which formed a ($\sqrt{2} \times 2\sqrt{2}$)R45$^{\rm o}$ superstructure. The effect of this intercalation on the graphene $\pi$ bands is to increase the offset of the Dirac crossing ($\sim$ -0.6 eV) and enlarge the gap ($\sim$ 350 meV). No such effect is observed for the graphene on Cu(111) sample, with the surface state at $\Gamma$ not showing the gap associated with a surface superstructure. The graphene film is found to protect the surface state from air exposure, with no change in the effective mass observed.
    Physical review. B, Condensed matter 08/2011; 84. · 3.77 Impact Factor
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    ABSTRACT: We prospectively investigated whether high intramedullary SI and contrast [gadolinium-diethylene-triamine-pentaacetic acid (Gd-DTPA)] enhancement in magnetic resonance imaging (MRI) are associated with postoperative prognosis in cervical compressive myelopathy (CCM) patients. Seventy-four patients with ventral cord compression at one or two levels underwent anterior cervical discectomy and fusion (ACDF) for CCM between March 2006 and June 2009. The mean follow-up period was 39.7 months (range, 12.7-55.7 months). The cervical cord compression ratio and clinical outcomes were measured using Japanese Orthopedic Association (JOA) scores for cervical myelopathy. Patients were classified into three groups based on the SI change in T2WI, T1-weighted images (T1WI), and contrast (Gd-DTPA) enhancement. The mean preoperative and postoperative JOA scores were 10.5 ± 2.9 and 15.0 ± 2.1 (P < 0.05), respectively. The mean recovery ratio of the JOA score was 70.9 ± 20.2%. There were statistically significant differences in postoperative JOA and recovery ratio among three groups. However, post-surgical neurological outcomes were not associated with age, symptom duration, preoperative JOA, and cord compression. We found that intramedullary SI change is a poor prognostic factor and the intramedullary contrast (Gd-DTPA) enhancement on preoperative MRI should be viewed as the worst predictor of surgical outcomes in cervical myelopathy. Contrast (Gd-DTPA) enhancement and postoperative MRI are useful for identifying the prognosis of patients with poor neurological recovery.
    European Spine Journal 07/2011; 20(12):2267-74. · 2.47 Impact Factor
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    ABSTRACT: No abstract available.
    Medical Principles and Practice 01/2011; 20(3):300. · 0.96 Impact Factor

Publication Stats

482 Citations
168.39 Total Impact Points

Institutions

  • 2005–2014
    • Yonsei University Hospital
      • Department of Internal Medicine
      Sŏul, Seoul, South Korea
  • 2013
    • Lawrence Berkeley National Laboratory
      • Advanced Light Source Facility
      Berkeley, CA, United States
    • Max Planck Society
      München, Bavaria, Germany
  • 2010–2011
    • Pohang University of Science and Technology
      • Department of Physics
      Andong, North Gyeongsang, South Korea
    • Korea Air Force Academy
      Sŏul, Seoul, South Korea
    • Pusan National University
      Tsau-liang-hai, Busan, South Korea
  • 2007–2009
    • Yonsei University
      • • College of Medicine
      • • Center for Atomic Wires and Layers
      Sŏul, Seoul, South Korea
  • 2008
    • National Health Insurance Corporation Ilsan Hospital
      Sŏul, Seoul, South Korea
    • Université de Sherbrooke
      Sherbrooke, Quebec, Canada
  • 2003–2008
    • Seoul National University
      • Department of Nuclear Engineering
      Seoul, Seoul, South Korea
    • Emory University
      • Department of Orthopaedics
      Atlanta, Georgia, United States
    • Chonbuk National University Hospital
      Sŏul, Seoul, South Korea