Distal junctional kyphosis in patients with Scheuermann’s disease: a retrospective radiographic analysis

Purpose To investigate the relationship between preoperative and postoperative spinopelvic alignment and occurrence of DJK/DJF. Study design/setting This was a retrospective observational cohort study. Patient sample The sample included 40 patients who underwent posterior correction of SK from January 2006 to December 2014. Outcome measures Correlation analysis between the preoperative and postoperative spinopelvic alignment parameters and development of DJK over the course of the study period were studied. Methods Whole spine X-rays obtained before surgery, 3 months after surgery and at the latest follow-up were analyzed. The following parameters were measured: maximum of thoracic kyphosis (TK), lumbar lordosis (LL), sagittal vertical axis (SVA), pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), lower instrumented vertebra (LIV) and LIV plumb line. Development of DJK was considered as the primary end point of the study. The patient population was split into a control and DJK group, with 34 patients and 6 patients, respectively. Statistic analysis was performed using unpaired t test for normal contribution and Mann–Whitney test for skew distributed values. The significance level was set to 0.05. Results DJK occurred in 15% (n = 6) over the study period. There was a significantly lower postoperative TK for the group with DJK (42.4 ± 5.3 vs 49.8 ± 6.7, p = 0.015). LIV plumb line showed higher negative values in the DJK group (−43.6 ± 25.1 vs −2.2 ± 17.8, p = 0.0435). Furthermore, postoperative LL changes were lower for the DJK group (33.84 ± 13.86% vs 31.77 ± 14.05, p < 0.0001.) The age of the patients who developed DJK was also significantly lower than that of the control group (16.8 ± 1.7 vs 19.6 ± 4.9, p = 0.0024.) Conclusions SK patients who developed DJK appeared to have a significantly higher degree of TK correction and more negative LIV plumb line. In addition, there may be a higher risk for DJK in patients undergoing corrective surgery at a younger age

Translation and validation study of the Iranian versions of the neck disability index and the neck pain and disability scale

STUDY DESIGN. Cultural translation and psychometric testing. OBJECTIVE. To translate and validate the Iranian versions of the Neck Disability Index (NDI-IR) and the Neck Pain and Disability Scale (NPDS-IR). SUMMARY OF BACKGROUND DATA. The widely used the NDI and the NPDS scales have not been translated and validated for Persian-speaking patients with neck pain. This was to provide a validated instrument to measure functional status in patients with neck pain in Iran. METHODS. The translation and cultural adaptation of the original questionnaires were carried out in accordance with the published guidelines. One hundred and eighty-five patients with neck pain were participated in the study. Patients were asked to complete a questionnaire booklet including the NDI-IR, the NPDS-IR, the Iranian SF-36, and a visual analog scale (VAS) of pain. To carry out the test-retest reliability, 30 randomly selected patients with neck pain were asked to complete the questionnaire booklet 48 hours later for the second time. RESULTS. Cronbach α coefficient for the NDI-IR was 0.88 and for the 4 subscales of the NPDS-IR was found to be satisfactory (ranging from 0.74 to 0.94). The NDI-IR and the NPDS-IR subscales showed excellent test-retest reliability (intraclass correlation coefficient ranged from 0.90 to 0.97; P < 0.01). The correlation between the NDI-IR and the NPDS-IR subscales and functional scales of the SF-36 showed desirable results, indicating a good convergent validity (Pearson correlation coefficients ranged from -0.31 to -0.70). The correlation between the NDI-IR and the VAS was 0.71 and between the NPDS-IR subscales and the VAS ranged from 0.63 to 0.79 (P < 0.01). CONCLUSION. The Iranian versions of the NDI and NPDS are reliable and valid instruments to measure functional status in Persian-speaking patients with neck pain in Iran. They are simple and easy to use and now can be applied in clinical settings and future outcome studies in Iran and other Persian speaking communities. © 2007 Lippincott Williams & Wilkins, Inc

The Effect of Ion-Channel Guiding on the Chaotic Electron Trajectories in a Free Electron Laser

It has been confirmed that when the equilibrium self-fields were taken into account, the motion of an electron in a helical wiggler with axial magnetic field may be chaotic. In this paper, the effect of an ion-channel guiding on the chaotic electron trajectories is analyzed. It is shown that the ion-channel guiding may modify the chaotic electron trajectories. It is also found that when the parameter ε, i.e. ε=ω$\text{}_{pb}^{2}$/4ω$\text{}_{c}^{2}$, is increased, the density of the ion-channel guiding, i.e. α$\text{}_{i}$=ω$\text{}_{pi}^{2}$/4ω$\text{}_{c}^{2}$, must be increased to keep the modification of the chaotic motion. The chaotic trajectories for constant parameter ε and increased density of the ion-channel guiding are presented. Numerical calculations are used to find the intersection between steady state group I and group II and resonance curves. Poincaré surface-of-section maps are generated to demonstrate the chaotic electron trajectories with axial magnetic field and its modification in the presence of an ion-channel guiding

Chaotic Electron Trajectories in a Planar Wiggler Free-Electron Laser

The motion of an electron in a planar wiggler with an axial guide field is found to be nonintegrable. When taking into account the effects of self-fields of the beam, it is confirmed that the motion of an electron in a planar wiggler with a guide field may be chaotic. There is evidence of chaos from numerical calculations of nonzero Lyapunov exponents using different approaches of Benettin's method which are described and compared. Very accurate Poincaré maps are also performed