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Background: Anterior cervical discectomy and fusion (ACDF) is widely used in the treatment of cervical degenerative disease; however, the variation of cervical sagittal alignment changes after ACDF has been rarely explored. The purpose of this study is to determine the relationship between changes of cervical sagittal alignment after ACDF and spino-pelvic sagittal alignment under Roussouly classification.Methods: A cohort of 133 Chinese cervical spondylotic patients who received ACDF from 2011 to 2012 was recruited. All patients were categorized with Roussouly Classification. Lateral X-ray images of global spine were obtained, and preoperative and postoperative parameters were measured and analyzed, including C2-C7 angles (C2-C7), C0-C7 angles (C0-C7), external auditory meatus (EAM) tilt, sacral slope (SS), thoracic kyphosis (TK), lumbar lordosis (LL), spinal sacral angles (SSA), Superior adjacent inter-vertebral angle (SAIV), inferior adjacent inter-vertebral angle (IAIV) and et al. The Wilcoxon signed-rank test was used for intragroup comparisons preoperatively and at postoperative 48 months.Results: Among the parameters, C2-C7 and C0-C7 showed significant increase, while EAM TK, and IAIV decreased significantly. In type I, EAM and TK decreased significantly, however SS showed a significant increase; in type II, TK showed a significant decrease, but SSA showed a significant increase; in type III, a significant increase of C0-C7 was observed with a significant decrease in EAM, nevertheless, LL, SS and SSA showed significant decreases; and in type IV, C2-C7 showed a significant increase and EAM decreased significantly. The percentage of lordotic alignment in cervical spine increased, which was presenting in type I, III and IV. Nevertheless, the amount of patients with straight cervical alignment increased in type II.Conclusion: The backward movement of head occurs is the compensatory mechanism in cervical sagittal alignment modifications after ACDF. The compensatory alteration of spino-pelvic sagittal alignment varied in different Roussouly type. [ABSTRACT FROM AUTHOR]

Background: Expandable screws have greater pullout strength than conventional screws. The purpose of this study was to compare the biomechanical stability provided by a new built-in expandable anterior spinal fixation system with that of 2 commonly used anterior fixation systems, the ZPlate and the Kaneda, in a porcine partial vertebral corpectomy model. Methods: Eighteen porcine thoracolumbar spine specimens were randomly divided into 3 groups of 6 each. A vertebral wedge osteotomy was performed by removing the anterior 2/3 of the L1 vertebral body and the T15/L1 disc. Vertebrae were fixed with the Z-Plate, Kaneda, or expandable fixation system. The 3-dimensional spinal range of motion (ROM) of specimens in the intact state (prior to osteotomy), injured state (after osteotomy), and after internal fixation were recorded. The pullout strength and maximum torque of common anterior screws, the expandable anterior fixation screw unexpanded, and the expandable anterior fixation screw expanded was tested. Results: After internal fixation, the expandable device and Z-plate system exhibited higher left bending motion than the Kaneda system (5.50° and 5.37° vs. 5.04, p = 0.001 and 0.008, respectively), and the Z-plate and Kaneda groups had significantly higher left axial and right axial rotation ROM as compared to the expandable device group (left axial rotation: 5.23° and 5.02° vs. 4.53°; right axial rotation: 5.23° and 5.08° vs. 4.49°). The maximum insertion torque of the expandable device was significantly greater than of a common screw (5.10 vs. 3.75 Ns). The maximum pullout force of the expandable device expanded was significantly higher than that of the common screw and the expandable device unexpanded (3,035.48 N vs. 1,827.38 N and 2,333.49 N). Conclusions: The built-in anterior fixation system provides better axial rotational stability as compared to the other 2 systems, and greater maximum torque and pullout strength than a common fixation screw. [ABSTRACT FROM AUTHOR]