Organic Broadband THz Generators Optimized for Efficient Near-Infrared Optical Pumping.

New organic THz generators are designed herein by molecular engineering of the refractive index, phonon mode, and spatial asymmetry. These benzothiazolium crystals simultaneously satisfy the crucial requirements for efficient THz wave generation, including having nonlinear optical chromophores with parallel alignment that provide large optical nonlinearity; good phase matching for enhancing the THz generation efficiency in the near-infrared region; strong intermolecular interactions that provide restraining THz self-absorption; high solubility that promotes good crystal growth ability; and a plate-like crystal morphology with excellent optical quality. Consequently, the as-grown benzothiazolium crystals exhibit excellent characteristics for THz wave generation, particularly at near-infrared pump wavelengths around 1100 nm, which is very promising given the availability of femtosecond laser sources at this wavelength, where current conventional THz generators deliver relatively low optical-to-THz conversion efficiencies. Compared to a 1.0-mm-thick ZnTe crystal as an inorganic benchmark, the 0.28-mm-thick benzothiazolium crystal yields a 19 times higher peak-to-peak THz electric field with a broader spectral bandwidth (>6.5 THz) when pumped at 1140 nm. The present work provides a valuable approach toward realizing organic crystals that can be pumped by near-infrared sources for efficient THz wave generation.

Accuracy and Safety in Screw Placement in the High Cervical Spine: Retrospective Analysis of O-arm-based Navigation-assisted C1 Lateral Mass and C2 Pedicle Screws.

STUDY DESIGN: This study was a retrospective analysis. OBJECTIVE: The purpose of present study was to evaluate accuracy, efficiency, and safety of intraoperative O-arm-based navigation system for the placement of C1 lateral mass screw (C1LMS) and C2 pedicle screws (C2PSs) in high cervical spine operations. SUMMARY OF BACKGROUND DATA: High screw misplacement rates, various pedicle morphometry and vertebral body size variations have led to a search of image-guided systems to improve the surgical accuracy of screw insertion in high cervical spine. The use of O-arm has been proposed for more accurate and efficient spinal instrumentation. MATERIALS AND METHODS: Between June 2009 and August 2016, a total of 48 patients with atlantoaxial instability were surgically treated using the image-guidance system. To reconstruct atlantoaxial instability, we have been using Harm's technique of C1LMS and C2PS fixations. A frameless, stereotactic O-arm-based image-guidance system was used for correct screw placement. Postoperative computed tomographic scan with multiplanar reconstructions were used to determine the accuracy of the screw placement. RESULTS: A total of 182 screws, including 90 C1LMS and 92 C2PSs were inserted using image-guidance system. In total, 4.4% (4/90) of C1LMS and 7.6% (10/92) of C2PS had cortex violation over 2 mm and considered as "significant." Among the significant cortex violations, "unexpected breech" was 3.3% of all the screws inserted. Two (2.1%) screws inserted had perforated the vertebral artery canal and iatrogenic vertebral artery stenosis was proved with postoperative computed tomography angiography. When divided into time periods, 60% of significant breech occurred during the beginning stage, 40% during adaptation stage and none during expert stage. CONCLUSIONS: In this study, the authors demonstrated that use of image-guidance system seems to be beneficial for high cervical instrumentation which requires much experience and steep learning curves. However, incidence of cortex violation does not disappear completely due to the close proximity to spinal canal and surrounding vessels.

Time Course of Radiologic Changes After Lumbar Total Disc Replacement: Experience of Single Institute With Minimum 5-Year Follow-up.

STUDY DESIGN: This was a retrospective observatory analysis study. OBJECTIVE: The purpose of this study was to evaluate long-term safety and therapeutic effectiveness of the lumbar total disc replacement (TDR) using ProDisc-L by analyzing the radiologic changes at the index and adjacent levels in minimum 5-year follow-up. SUMMARY OF BACKGROUND DATA: Early successful clinical results of lumbar TDR have been reported. However, few reports have published its therapeutic effectiveness and radiologic degenerative changes at the index and adjacent segments in the long term. MATERIALS AND METHODS: Forty-three patients were followed-up for at least 60 months. Radiologic changes were assessed by segmental range of motion (ROM) at the index and adjacent levels, global lumbar lordosis, and disc space height (DSH). The magnetic resonance imaging and computed tomographic scans were used to determine the facet arthrosis and intervertebral disc degeneration at the index and adjacent levels. RESULTS: Gradual decrements of DSH restoration were observed until the last follow-up. Mean global and segmental ROM of index segments were significantly reduced (P=0.044, 0.00) at the last visit. There were 21 patients (48.8%) with no motion at index segment (ROM<0.5 degrees) at the last visit. Among the 56 segments operated on, progression of facet arthrosis was observed in 30.3% of index segments and 10.9% of adjacent segments. None of the postoperative radiologic parameters included in the present study presented significant correlation with clinical outcome. CONCLUSIONS: The study demonstrates that only half of the lumbar TDR patients can maintain segmental motion at the index level >5-year after surgery and TDR provides a good clinical outcome postoperatively regardless of motion preservation or DSH height preservation at the last follow-up. After TDR, the degenerative changes in the index and adjacent segments advanced as compared with our previous report of 2-year follow-up, however, these changes did not appear to exert negative influence upon clinical outcomes.

Minimally invasive posterior cervical decompression using tubular retractor: The technical note and early clinical outcome.

BACKGROUND: The aim of this work is to present a novel decompression technique that approaches cervical spine posteriorly, but through minimal invasive method using tubular retractor avoiding detachment of posterior musculature. METHODS: Six patients underwent minimally invasive posterior cervical decompression using the tubular retractor system and surgical microscope. Minimally invasive access to the posterior cervical spine was performed with exposure through a paramedian muscle-splitting approach. With the assistance of a specialized tubular retraction system and deep soft tissue expansion mechanism, multilevel posterior cervical decompression could be accomplished. This approach also allows safe docking of the retractor system on the lateral mass, thus avoiding the cervical spinal canal during exposure. A standard operating microscope was used with ×10 magnification and 400 mm focal length. The hospital charts, magnetic resonance imaging studies, and follow-up records of all the patients were reviewed. Outcome was assessed by neurological status and visual analog scale (VAS) for neck and arm pain. RESULTS: There was no significant complication related to operation. The follow-up time was 4-12 months (mean, 9 months). Muscle weakness improved in all patients; sensory deficits resolved in four patients and improved in two patients. Analysis of the mean VAS for radicular pain and VAS for neck pain showed significant improvement. CONCLUSIONS: The preliminary experiences with good clinical outcome seem to promise that this minimally invasive technique is a valid alternative option for the treatment of cervical spondylotic myelopathy.